The Institute for Astronomy at the University of Hawaii is developing a large optical synoptic survey telescope system; the Panoramic Survey Telescope and Rapid Response System. Pan-STARRS will consist of an array of four 1.8m telescopes with very large (7 square degree) field of view, giving it an etendue larger than all existing survey instruments combined. Each telescope will be equipped with a 1 billion pixel CCD camera with low noise and rapid read-out, and the data will be reduced in near real time to produce both cumulative static sky and difference images, from which transient, moving and variable objects can be detected. Pan-STARRS will be able to survey up to ≈6,000 square degrees per night to a detection limit of approximately 24th magnitude. This unique combination of sensitivity and rate of area coverage will open up many new possibilities in time domain astronomy. A major goal for the project is to survey potentially dangerous asteroids, where Pan-STARRS will be able to detect most objects down to 300m size, much smaller than the km size objects accessible to existing search programs. In addition, the Pan-STARRS data products will used to address a wide range of astronomical problems in the Solar System, the Galaxy, and the Cosmos at large. Here, we first outline the Pan-STARRS science goals and describe the survey modes needed to support these. We then describe the design and performance goals, the data processing pipeline, and we review the basic data products. Finally, we present results from simulations that demonstrate Pan-STARRS' capability for detecting potentially hazardous asteroids.

Programmes driving ELT design are discussed. The nature and evolution of circum-stellar shells and planetary discs are attractive, while the small angular sizes place basic properties, asymmetry and warps, beyond VLT capability. An ELT is neeed to reveal the conversion processes shell - disc - planets, planetary systems, Earth-like planets, habitability and life signatures. Formation and evolution of massive stars are dicussed as are stellar rotation and shape, surface spatial and temporal resolution and evolution. Stellar clusters are discussed as probes of galactic evolution, resolving CMDs for Virgo and Fornax cluster galaxies. High-resolution studies of AGNs are discussed as are supernovae with bearing on early star formation, galactic activity and cosmology. Finally, the requirements defined from the prime science drivers are confronted with technical realities.

We present an overview of the science case for a 50-100m Extremely Large Telescope. This was the subject of a meeting in Marseilles, France in November 2003, attended by about 50 European astronomers. Four key scientific themes were identified by the participants: terrestrial planets in extra-solar systems; stellar populations across the Universe; building galaxies since the darkest ages; the first objects and re-ionisation structure of the Universe. Although by no means an exhaustive list of science areas in which ELT will have a great impact, these cases provide examples where an ELT can make a dramatic advance in our understanding of the Universe around us. This paper describes these highlighted science themes and the challenging demands they place on ELT performance. See http://www-astro.physics.ox.ac.uk/~imh/ELT/ for more information, including the full list of participants in this work.

We describe the scientific case and design challenges for an innovative large submillimetre telescope (LST). LST is proposed to have a diameter of at least 30m, operate in the wavelength range from 0.2 - 1mm and will have a wide field-of-view. The submillimetre region allows us to probe objects during formation - i.e. the earliest evolutionary stages of galaxies, stars and planets. Being so close to the peak of the cosmic far-IR/submm background and the emission from proto-stellar cores, the 200μm atmospheric window gives access to unique science. The key advantage of LST over other facilities will be in terms of addressing astronomical questions requiring large fields and good angular resolution: such as surveys of entire giant molecular clouds and fields of dusty galaxies at early epochs. For example, such a telescope would resolve all protoplanetary disks out to 100pc, revolutionising our knowledge of star and planet formation, and detect tens of millions of dusty high-redshift galaxies yielding information on formation and evolution of the early universe. Equipped with a state-of-the-art large format bolometer camera, LST would offer a survey (mapping) speed up to 5,000 times that of ALMA, arcsecond resolution at the shortest wavelengths, point-source sensitivities at least 25 times better than any planned submm facility, and confusion limits 10 times lower than any existing single-aperture telescope. The wide-field-of-view and superb image fidelity available from a single-dish will be perfect for large-scale surveys of the submillimetre sky - an ideal complement to new generation interferometers such as ALMA.

The Square Kilometre Array (SKA) is a global project to design and build a new generation radio telescope at metre to centimetre wavelengths. It will have a collecting area of order one million square metres, a sensitivity 100 times higher than the VLA, an instantaneous field of view (FOV) of at least 1 square degree and, in some designs, more than one FOV allowing multiple simultaneous use. It will be an extremely powerful survey telescope with the capability to follow up individual objects with high angular and time resolution. The SKA will reach a point source sensitivity of 10 nano-Jy in 8 hours of integration, and a maximum resolution of 1 milli arcsec at 20 GHz with excellent imaging capability at all resolutions and frequencies. The SKA science impact will be felt in astro-particle physics and cosmology, fundamental physics, galactic and extragalactic astronomy, and solar system science. Technological innovation, closely paralleling commercial IT developments, is key to the design concepts under investigation and to the cost goal of USD1000/m2. The selection of technologies for the SKA is scheduled in early 2008. A number of possible locations for the telescope are under investigation with a choice scheduled in early 2006. Construction of the array will take most of the next decade.

I describe the procedures used during the different phases of site testing for astronomical telescopes, that is, during the pre-selection of candidate sites, on-site testing (site selection), the site decision itself and characterization of the telescope site once the decision has been made. Many of the important parameters for astronomical night-time telescopes and some of the methods that can be used to determine these parameters are described. There appear to be no fundamental differences between the methods used for telescopes in the 5 to 10 meter range and telescopes with diameters larger than 10 meters, although specific differences certainly exist.

Selection of an ideal site for the new generation of Overwhelmingly Large (OWL) telescopes is dependent on many climatological and meteorological parameters. Among these are cloud cover, atmospheric humidity, aerosol content, air temperature, airflow direction, strength and turbulence. Even relatively minor changes in weather patterns can have a significant effect on seeing conditions. A composite climatological database has been designed and built for the site selection task at the Department of Geosciences, University of Fribourg, Switzerland. The database is mainly composed of ECMWF and NCEP-NCAR reanalysis data at a global resolution of between 1° and 2.5° latitude / longitude. Using a Java based interface, codenamed "FriOWL", and programmed in the style of a Geographical Information System, all of this relevant information can be interrogated in order to find the best possible sites for the new telescope. Perhaps the most important variable in site selection is the interaction between air-flow and topography, as atmospheric turbulence greatly affects the image quality produced by the telescope. Global climate is changing and it will continue to do throughout the 21st century. Therefore, it is important to ascertain the effect of global warming on potential sites. An ideal site in today’s climate may not prove ideal within 20 to 50 years. It is therefore planned to update the database with future climate data, using output from global climate models. High resolution modeling of the critical parameters at preferred sites under future climates is also planned.

The ESO OWL site survey plan includes the analysis of the astronomical quality of the Atlas mountains in Morocco. In this paper we are presenting the first long time measurement of optical turbulence at Oukaimeden site. For this work we built an instrument called ADIMM for an Automated Differencial Image Motion Monitor, and we use it to the measure the optical turbulence at the Oukaimeden Site. We are describing the instrument and reporting the first results obtained after six month of working on this project. The results of night-time seeing measurements carried out during the period from Jun 14 up to October 01 2003 are presented. The median and mean values of the seeing for the entire period of observations are respectively 0.75" and 0.84". This work was organized in the framework of contract Num.69651/ODG/02/9005/GWI between the European Southern Observatory (ESO) and Astrophysics and Physics of High Energy Laboratory of the Faculty of Sciences, Cadi Ayyad University (LPHEA).

The location of the Advanced Technology Solar Telescope (ATST) is a critical factor in the overall performance of the telescope. We have developed a set of instrumentation to measure daytime seeing, sky brightness, cloud cover, water vapor, dust levels, and weather. The instruments have been located at six sites for periods of one to two years. Here we describe the sites and instrumentation, discuss the data reduction, and present some preliminary results. We demonstrate that it is possible to estimate seeing as a function of height near the ground with an array of scintillometers, and that there is a distinct qualitative difference in daytime seeing between sites with or without a nearby lake.

Climate diagnostic archives appears to be a very useful tool for astronomical site assessment. These climatological databases combine data from meteorological archives for different data sources (radiosoundings, satellites, etc) and meteorological models to derived any parameter at a particular selected location. Although the products from climate diagnostic archives are heavily constrained by observational data, a rigorous control of data quality, analysis and cross comparison needs to be performed before the method becomes extensively used for site characterisation. In this talk we present an statistical analysis of winds, an important parameter for site characterisation, using in-situ measurements (ground level and balloon data) and data derive from climate diagnostic archives. The cross-comparison of results obtained from the two set of data allow us to propose some restrictions in the use of climate diagnostic products for site characterisation.

We combined aerosol index measurements of TOMS/Nimbus-7 and Earth Probe observations with CAMC visual extinction over La Palma from 1984 to 1997, to investigate the possibility to calibrate TOMS data in terms of astronomical extinction. The results show that the correlation of the two sets of data is quite good for extinction values greater than about Av = 0.2 mag./airmass. A detailed analysis reveals that the satellite aerosol index is indeed sensitive to the desert dust, but does not show evidence of the extinction contribution of the volcanic smoke due to the Mt. Pinatubo eruption which affected astronomical observations in 1992-1993. This calibrated aerosol index is then used to investigate the number and distribution of dusty events over the astronomical site of Oukaimeden, Morocco. We find a remarkable correlation of the extinction over the two sites. Finally we study the long term variability of the extinction over the region including Oukaimeden and La Palma, and we conclude that there is some correlation with the Northern Atlantic Oscillation.

The first of the Unit telescopes of the VLT has now been in operation for 5 years. The complete array has been producing scientific results since 2001 and the VLTI has in the past few months celebrated common user status with MIDI on the Unit telescopes. With the first of four auxiliary telescope already on site and VST and VISTA in construction, Paranal observatory is rapidly reaching maturity. Combining the power of these facilities with service observing and full user support the VLT is already having a significant impact on astronomy. In this paper we review our operations and present some metrics of what we believe is success.

The Subaru Telescope has been stably operated with high image quality since common use began in December 2000. We have updated the following items in order to achieve further improvement of observation efficiency, image quality, and tracking. 1. High reflectivity of mirrors. The reflectivity of the primary mirror has been maintained, yielding 84% at 670 nm by regular CO₂ cleaning (every two to three weeks). We successfully carried out the silver coating of the Infrared secondary mirror in April 2003 without over-coating. The reflectivity has been maintained at greater 98% at 1,300 nm. 2. Image Quality. Subaru telescope delivers exceptional image quality {a median image size of 0.6 arc-second FWHM in the R-band as taken by Auto-Guider Cameras at all four foci; Prime, Cassegrain, and two Nasmyth. We optimized parameters of the servo control system of the Elevation servo, reducing the amplitude of 3{8 Hz vibration mode of the telescope and improving image quality when using the Adaptive Optics (AO) system. 3. Acquisition Guiding. Dithering time was shortened by updating the control software. The slit viewer camera for HDS and the fiber bundle for FMOS are available for acquisition guiding in addition to Auto-Guider Cameras. 4. New instruments. We are developing a new prime focus unit for FMOS and will start functional tests in 2005. Moreover, we have started to prepare new interfaces and facilities for FMOS and the new 188 element AO natural/laser guide star system. The focus switching time will be shortened by updating the hardware of the IR and Cassegrain Optical secondary mirrors from September 2004, reducing it to 10 minutes to switch the focus between Cassegrain and Nasmyth foci.

The Hobby-Eberly Telescope (HET) is a fixed-elevation, 9.2-m telescope with a spherical primary mirror and a tracker at prime focus to follow astronomical objects. The telescope was constructed for $13.9M over the period 1994-1997. A series of extensive engineering upgrades and corrective actions have been completed recently, resulting in significantly improved delivered image quality and increased operational efficiency. The telescope's Spherical Aberration Corrector (SAC) optics were recoated with a highly reflective and durable broadband coating at Lawrence Livermore National Laboratory. The software mount model that maintains optical alignment of the SAC with the 11-m primary mirror array was recalibrated and improved. The acquisition and guiding optics for both the High Resolution Spectrograph (HRS) and the Low Resolution Spectrograph (LRS) were reworked and improved, allowing for better focus and SAC alignment monitoring and control. Recoating of the primary mirror segment array was begun. Telescope images of 0.82 arcseconds have been recorded for sustained periods in preliminary testing following the engineering upgrade, an improvement of 50% over previous best performance. Additional engineering upgrades are scheduled to consolidate these performance gains and to continue improving delivered image quality, throughput, and telescope operational efficiency. The HET is now capable of the science performance for which it was designed.

Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.

The NRAO Robert C. Byrd Green Bank Telescope is a new 100 meter radio telescope that is now in routine astronomical operation. This paper gives a status report on astronomical performance, operational capabilities, development plans, and early scientific highlights. The telescope is now in regular operation to frequencies of 50 GHz, which achieves the base design goal of the facility. Both the surface and pointing accuracies allow good performance at that frequency. The active surface of 2004 movable panels is in regular use at all frequencies above ~8 GHz and significantly improves both gain and diffraction beam shape at high and low elevation angles. Receivers exist at most primary observing frequencies ranging from ~290 MHz to 50 GHz. A 256k-channel correlation spectrometer with up to 16 independent inputs is in routine use for spectroscopy. Backends for pulsar observing, broadband continuum, Very Long Baseline Interferometry, and planetary radar reception also exist. An advanced development program for enhancing the performance of the GBT is also underway. This program includes the Precision Telescope Control Project that will extend operation to 115 GHz or 2.6 mm wavelength (see the paper by Prestage and Constantikes in this volume), a 26-40 GHz receiver, a 68-92 GHz receiver, a fast sampling continuum backend built by a Caltech/NRAO collaboration, and a 64-pixel bolometer camera developed by a consortium of UPenn, NASA-GSFC, NIST, UCardiff, and NRAO. Software development projects for enhanced user interfaces and data handling are underway, and plans to implement queue-based dynamic scheduling and remote observing are being developed. The status of these projects and their anticipated scientific impact will be discussed.

Technological advances are changing the nature of VLBI. Disk based recording has already led to sustantial increases in sensitivity and with the advent of new telescopes and data acquisition systems VLBI will start penetrating the micro-Jansky sky. With the employment of fibre based communication networks as the basis for production, real-time VLBI networks will become a reality. This changes the way VLBI is done and removes bottlenecks in operation and scientific exploration. At the output side, fantastic new correlator output data rates and the ability to deal with these via powerful PC clusters promises to expand the typical VLBI field-of-view to scales previously reserved for connected, short baseline interferometers. These developments require new algorithms for user processing, as well as new interfaces to present the product to the users.

e-MERLIN is an upgrade to the MERLIN array of seven radio telescopes spread across England, which will increase its sensitivity by more than a factor or 30. The combination of μJy sensitivity with the 50-mas resolution already provided by the long baselines of MERLIN, will open new avenues of research for e-MERLIN. The huge increase in bandwidth is achieved by replacing the exiting microwave links with new optical fibre connections. To collect and correlate this wide bandwidth, new receivers, IF and sampling equipment, digital and optical transmission equipment and a new wideband correlator are being designed and constructed. This paper summarises the design goals, scientific objectives and implementation of e-MERLIN.

Progress in the conceptual design phase of ESO's OWL 100-m optical and near-infrared telescope is reported, with emphasis on the development of the science case. The Phase A opto-mechanical design is now basically completed, and provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. We also report about the latest outcome of industrial studies, introduce the essential definition of the wavefront control systems, and outline operational concepts and instruments priorities. Finally, we elaborate on the favorable cost factors associated to the telescope design, its compatibility with low industrial risks, and argue that progressive implementation allows for competitive timescales. In particular, we show that suitable fabrication and integration schemes should accommodate for a start of science operation at unequalled potential and within a time frame comparable to that of smaller designs, while at the same time maximizing R&D time for critical subsystems.

The Euro50 is an extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. It has a segmented, aspherical primary mirror and an aspherical, deformable secondary in a Gregorian layout. A tentative conceptual design exists and has been documented in a study report. Recent activities have concentrated on the science case for extremely large telescopes in the 50 m class and on identification of potential technical "show stoppers". The science case investigation has identified four fields of particular interest. The studies of critical technical issues have concentrated on atmospheric dispersion effects for high-resolution adaptive optics for extremely large telescopes, and on the influence of wind and other disturbances on wavefront control. Wind load on the telescope, the primary mirror and the enclosure has been studied using wind tunnel measurements and computational fluid dynamics. The impact of wind on the total system has been investigated using an integrated model that includes the telescope structure, the primary mirror segment alignment system, the secondary mirror alignment system, and single conjugate adaptive optics using the deformable secondary mirror. The first, tentative results show that wind disturbances may be significant and that the task of correcting for wind residuals may be at least as large for the adaptive optics system as that of correcting for atmospheric aberrations. The results suggest that use of extremely large telescopes for observations of earth-like planets around nearby stars may imply a considerable challenge.

The status of activites on the future planning of the optical and infrared astronomy community of Japan is reported. The community established a working group to draw a concrete plan for ground based telescopes and space missions for the next decades. Reported in this paper are the basic concept developed for extremely large telescope. Some specific areas of related research and development, for instance optical design, new materials for segmented mirrors, new approach to fabricate aspheric segmented mirror, and other engineering activities. These might turn out to be useful for promoting the project. Japan's community is open for international collaborations in these areas.

This telescope has 30m aperture, segmented primary mirror and alt-azimuth mounting. The aspherical primary mirror with f-ratio 1.2 consists of 1122 partial annular submirrors. The optical system includes Nasmyth I and II systems, Cassegrain system, coude system and a wide field of view system. There are four Nasmyth platforms. Two Nasmyth I foci are located on the upper floor and two Nasmyth II foci are located in the lower floor. All Nasmyth I, II and Cassegrain systems use same one secondary mirror, and all are R-C systems. With adaptive optics system, several diffraction-limited observations can be operated simultaneously on Nasmyth II platforms. The wide field of view system has 20 arcmin FOV, can correct atmospheric dispersion and the low space frequency error from primary mirror and atmosphere turbulence. A special rocking chair structure is designed which can realize the horizontal axis on the front of primary mirror. The tolerances of the surface shape and position of submirrors are given. The issues about tip-tilt correction and adaptive optics are discussed. Some formulae on rotating conic surface especially used for segmented mirror are given.

The Giant Magellan Telescope (GMT) is a joint project of a consortium of universities and research institutions to build and operate a 21.5-m equivalent aperture astronomical telescope for use at visible and IR wavelengths. This paper briefly summarizes the science goals for the project and provides an overview of the preliminary telescope and enclosure concepts and site test program. The telescope is a Gregorian design with a fast, f/0.7, primary mirror that allows a compact and stiff mount structure. The 25.3-meter diameter primary mirror consists of six off-axis 8.4-meter circular mirrors arranged in a hexagon around a center 8.4-meter mirror. The Gregorian secondary mirror is adaptive allowing two-mirror, wide-field adaptive optics. Several corrector designs have been studied for wide-field applications and one such design is shown. Instruments being considered for GMT provide a wide range of scientific capabilities. Instruments mount below the primary mirror on an instrument platform. Instrument mounting and servicing provisions are summarized.

The science case for wide fields on ELTs is well developed and justifies the implementation of 20 arc-minute and larger fields-of-view with seeing-limited performance on a 20 to 30-meter telescope. However, the practical implementation of a wide field can prove to be challenging with classical telescope design when low-thermal emissivity performance is also being optimized. Segmented mirrors assemblies need not be full aperture, axially symmetric structures. Space for secondary, tertiary, and quaternary mirror support structures that do not cross the optical path can be achieved with off-axis mirror assemblies. Barden, Harmer, Claver, and Dey described a 4-mirror, 1-degree FOV 30-meter telescope. We take that concept further with an off-axis approach. Three conic mirrors are required to produce excellent image quality in the 1-degree FOV (diffraction limited across the central few arc-minutes, better than 0.3" imaging performance at the edge of the field). A flat quaternary mirror is utilized both as a beam steering mirror to different instrument ports on the lower side of the telescope and as an adaptive mirror for wind-buffeting and possible ground layer AO correction. The final f/2.2 focal ratio allows the use of an echidna-style fiber positioner for very dense target field acquisition. Extreme AO and Ground Layer AO ports can both be implemented as well. Diffraction characteristics may possibly be improved given the lack of a spider mount for the secondary mirror but will be elliptical rather than circular.

We present a design concept for a 16 metre, wide-field, fixed-axis, all-reflective, segmented f/4 Schmidt telescope to take advantage of the unique possibilities of Antarctica for both optical and near infrared astronomy. The design allows observation of all RA/dec's accessible from Antarctica, with tracking times of several hours. Prime and Cassegrain foci are provided, giving plate scales 300-3000microns/", over fields of view 1.5'-0.5°. Diffraction limited, natural guide-star AO-corrected Kdark images are possible over arc-minute sized fields, over 70% of the sky. The sensitivity, resolution, field of view and cost all compare favourably with current or proposed space or ground-based telescopes.

We have proposed to develop a prototype 0.5-meter far-infrared telescope and heterodyne receiver/spectrometer system for fully-automated remote operation at the summit of Dome A, the highest point on the Antarctic plateau. The unparalleled stability, exceptional dryness, low wind and extreme cold make Dome A a ground-based site without equal for astronomy at infrared and submillimeter wavelengths. HEAT, the High Elevation Antarctic Terahertz Telescope, will operate in the atmospheric windows between 150 and 400 microns, in which the most crucial astrophysical spectral diagnostics of the formation of galaxies, stars, planets, and life are found. At these wavelengths, HEAT will have high aperture efficiency and excellent atmospheric transmission most of the year. The proposed superheterodyne receiver system will be comprised of 0.8, 1.4 and 1.9 THz channels which will observe the pivotal J=7-6 line of CO, the J=2-1 line of atomic carbon, and the far-infrared fine structure lines of N+ and C+, the brightest emission lines in the entire Milky Way Galaxy. When combined with the HEAT telescope, the receiver system represents a uniquely powerful instrument for reconstructing the history of star formation in our Galaxy, with application to the distant Universe. The receiver system itself serves as a valuable testbed for heterodyne Terahertz components, using leading-edge mixer, local oscillator, low-noise amplifier, cryogenic, and digital signal processing technologies that will play essential roles in future Terahertz observatories. The proposed study will pave the way for future astronomical investigations from Dome A.

Wide-Field imaging at visible wavelengths with seeing of the order of 0.1-0.2arcsec is believed to be possible from the high Antarctic plateau site of Dome-C by the removal of ground layer effects only. We present a proposal for a 2m-class telescope specifically designed for the science case of short duration (~10s or greater) microlensing events in the crowded central regions of Galactic Globular Clusters and nearby galaxies where the achievement of a spatial resolution of the order of a fraction of arcsec is essential. The philosophy behind the telescope proposal is discussed in detail. It is emphasized that this is a project with a specific unique science goal in mind and not a large scale facility instrument. A preliminary design for the optics, ground layer removal using a deformable secondary and "static" wavefront sensor and telescope structure is presented. In particular, it is shown that substantial simplification in the design can be achieved by having a specific science goal in mind, so reducing the complexity and increasing reliability. Transport and logistics for the successful deployment and operation of the telescope at the Dome-C site are discussed.

A concept is presented for an extremely large high-resolution solar telescope with an aperture of 11 m and diffraction limited for visual wavelengths. The structure of GISOT will be transparent to wind and placed on a transparent stiff tower. For efficient wind flushing, all optics, including the primary mirror, will be located above the elevation axis. The aperture will be of the order of 11 m, not rotatively symmetrical, but of an elongated shape with dimensions 11 x 4 m. It consists of a central on-axis 4 m mirror with on both sides 3 pieces of 2 m mirrors. The optical layout will be kept simple to guarantee quality and minimize stray light. A Coudé room for instruments is planned below the telescope. The telescope will not be housed in a dome-like construction, which interferes with the open principle. Instead the telescope will be protected by a foldable tent construction with a diameter of the order of 30 m, which doesn’t form any obstruction during observations, but can withstand the severe weather circumstances on mountain sites. Because of the nature of the solar scene, extremely high resolution in only one dimension is sufficient to solve many exciting problems in solar physics and in this respect the concept of GISOT is very promising.

Previously the effect of atmospheric dispersion on telescope performance has attracted only relatively little attention. This may be due to the fact that the dispersion effects have been evaluated in relation to the size of the diffraction limited resolution angle of current telescopes, or to seeing limited telescopes. However, since the resolution angle is inversely proportional to telescope diameter, dispersion and dispersion compensation becomes increasingly important for extremely large telescopes (ELTs). In this paper we present a simple model for the dispersion effects in telescopes with adaptive optics (AO). The model addresses the expected loss in Strehl ratio when the atmospheric wavefront error is measured at a wavelength different from the wavelength of observation. Also, the bandwidth over which the correction will be of a given quality is evaluated. Related to AO performance, the consequence of using laser guide stars (LGSs) for probing the atmosphere may be that the measured wavefront error must be rescaled to the wavelength of observation. This places special demands on the AO control loop. Since linear atmospheric dispersion compensation need not cover a larger bandwidth than the AO compensation, an atmospheric dispersion compensator (ADC) can be designed for narrow band operation. As an example of the benefits to be obtained from this, we briefly present the proposed ADC for the Euro50.

During last decade, several concepts for the next generation of telescopes have evolved into well-established projects. The majority of the proposed concepts are Extremely Large Telescopes (ELTs) utilizing the advantages of having an AO system as an integrated part of the main optical system. An adaptive secondary mirror (AS) has become a typical prerequisite for the future ground-based optical telescopes. Recent advances in deformable mirror technology used for AS mirrors show a possibility of developing this technology to the mirrors of larger diameters suitable for integration into ELT main optical systems. An idea of fully adaptive telescope has been proposed for the Arcetri 40-m multi-conjugate telescope. A four-mirror optical system with a 40 m parabolic segmented primary is considered and optimised for such an advanced ELT. It is shown that the proposed system geometry enables to obtain proper optical conjugation for the tertiary and quaternary mirrors, achieving a diffraction limited image quality over 8-arcmin field. The aspects of internal vignetting and re-imaging of laser guide stars are discussed. If the fabrication of adaptive mirrors of a large size is feasible, the proposed four-mirror system will become highly attractive in terms of system compactness and minimized number of mirrors employed in the ELT multi-conjugate AO system.

Presently the ground-based High Energy Stereoscopic System (H.E.S.S.) with 12 m Cherenkov telescopes is used for very high energy gamma ray astronomy. With these telescopes the Cherenkov light which is generated when cosmic gamma rays are absorbed by the atmosphere is collected by the mirror dishes of these optical telescopes and recorded by digital cameras for further examination. This existing H.E.S.S. Phase I system in Namibia erected and operated by the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany, uses four 12 m telescopes arranged in the corners of a 120 m square for best sensitivity. The next step in order to increase the exploitation of the gamma rays in the atmosphere is to use bigger Cherenkov telescopes with a lower threshold and improved sensitivity. In this paper the results of a feasibility study on the design of Large Cherenkov Telescopes with diameters of up to 30 m are presented. The feasibility investigations done by MAN Technologie in Mainz, Germany had to take into account the required mechanical performance, costs, and local fabrication and erection capabilities of the countries in which the telescopes should be erected.

Aperture plane detection of cosmic radio signals can confer several important advantages. The mechanical signal processing of conventional parabolic dish antennas can be replaced by signal processing purely in electronics and software, thereby placing aperture plane array instruments in a regime with decreasing future costs. Aperture arrays using all-sky element antennas also allow multiple, independent, full sensitivity telescopes to be formed in software. The Low Frequency Array (LOFAR) project aims to realize these advantages in a previously largely unexplored frequency domain, 10-240 MHz. Consisting of up to eight shared aperture telescopes operated independently over internet, it will explore the epoch of re-ionization, open the transient radio Universe to systematic study, record ultra-high energy cosmic particles and add a new dimension to solar and space physics research.

The GTC (Gran Telescopio Canarias) is a 10,4 meter segmented telescope currently being integrated at the ORM in La Palma, Spain. It is a partnership between Spain, Mexico and the University of Florida. Main science drivers for the GTC are image quality, operational efficiency and reliability. First light is planned for mid-2005. The GTC Project, initiated in 1996, is well advanced in its integration. Construction started in October 1999. The main building and dome were finished by end 2002 and are now enclosing the assembly work of the telescope structure. All telescope subsystems are finished and in La Palma where the telescope structure keeps growing. The segments of the primary mirror, probably one of the most demanding part of the GTC, have also started to be delivered by the polisher. Three science instruments are starting their integration and are expected to arrive at the telescope well on time. Two second-generation instruments, including one exploiting the future Adaptive Optics capabilities of the GTC, are under development. Preparation for operation and maintenance has started to ensure a smooth transition from construction into the operation phase. The current status of the project and the short term plans are presented here.

The Southern African Large Telescope (SALT) is a 10-m class telescope for optical/infrared astronomy based on the tilted Arecibo design first adopted by the Hobby Eberly Telescope. SALT is being constructed by a consortium consisting of 11 partners from six countries. SALT will enable a quantum leap in astronomical research capability in the African continent, where currently the largest telescope is a modest 1.9-m, dating to the 1940s. The SALT Project was approved in November 1999, the SALT project team started in January 2000, groundbreaking followed in September, the first mirror segment was installed in December 2002, and On-Sky Testing started in October 2003. SALT is due to start operations by 2005. The commissioning instrument has been developed by the South African Astronomical Observatory and the other first-light instrument is being developed by the University of Wisconsin-Madison. The major technical challenges in SALT are the alignment of the 91 identical spherical mirror segments, the position feedback of the prime focus tracker, and the dome seeing associated with large enclosures at a site with large daily thermal cycles. All of these issues were addressed thoroughly during the design phase, and first tests are showing very positive results in all these areas. This paper will summarize the international partnership in SALT and the management and organisation of the project and then address (1) the basic design, with emphasis on the technical challenges (2) the specified performance of SALT, (3) the progress and status of the project, including first light instruments.

The Large Binocular Telescope (LBT) Project is a collaboration between institutions in Arizona, Germany, Italy, and Ohio. The telescope uses two 8.4-meter diameter primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8-meter circular aperture. A unique feature of LBT is that the light from the two primary mirrors can be combined to produce phased array imaging of an extended field. This coherent imaging gives the telescope the diffraction-limited resolution of a 22.65-meter telescope. The first of two 8.4-meter borosilicate honeycomb primary mirrors has been installed in the telescope on Mt. Graham in southeastern Arizona. First Light is planned for later this year with one primary mirror and a prime focus imager. The second of the two primaries is being polished at the Steward Observatory Mirror Lab in Tucson and will be installed in the telescope in the Fall of 2005. The telescope uses two F/15 adaptive secondaries to correct atmospheric turbulence.

Development of the 4.1 meter SOuthern Astrophysical Research (SOAR) Telescope is now complete. All baseline systems are in place and extensive commissioning activities have been performed with and without the primary optics installed in the telescope. The facility and dome have been under observatory operations and TCS control for a year of testing and tuning. The altitude over azimuth telescope mount was integrated on the mountain in a rapid 3-month period due to the complete assembly and testing performed at the factory prior to delivery. Early mount testing and successful integration into the Telescope Control System (TCS) without the optical system was accomplished on the sky through use of two separate small aperture telescopes fixed to the structure. One of these, the "feed telescope" was also pivotal in early testing of the calibration wavefront sensor and SOAR optical imager by directing focused light to these separate instruments. The SOAR optical system, with its 4.1 meter clear aperture, 100 cm thick, ULEtm primary mirror, its lightweight ULEtm secondary, and its fast tip tilt ULEtm tertiary has been delivered and installed in the telescope. This system was also assembled as an electrically connected system and individually optically tested under a visible interferometer at the factory enabling rapid integration and a short commissioning period on telescope. In this paper we present the project status, a summary of the commissioning period, and the performance data for the completed telescope and its major components.

The Advance Technology Solar Telescope (ATST) has finished its conceptual design stage, submitted a proposal for construction funding and is working towards a system level preliminary design review later this year. The current concept (including integrated adaptive optics and instrumentation) will be reviewed with concentration on solutions to the unique engineering challenges for a four meter solar telescope that have been previously presented. The overall status will be given with a concentration on near term milestones and impact on final completion targeted in 2012.

The Visible and Infrared Survey Telescope for Astronomy (VISTA) project started in 2000 following a Joint Infrastructure Fund award to a consortium of 18 Universities within the UK. The UK ATC was contracted to manage the project of developing and building the VISTA facility. VISTA is planned to be a 4-m class telescope with the ability to mount both a visible and infra-red cameras, not concurrently. The design has an F/1 primary resulting in some demanding design issues. The project has now entered its detailed design and manufacturing phase. As we have contracted out major items a coordinated approach to the management of budgets, through systems engineering, risks, through risk management, and safety, through the generation of safety cases, had to be generated. These have been developed through the current phase, and control of the interfaces and science requirements has been maintained. The project is further developing the systems engineering and safety management to generate the commissioning plan and the overall safety case. The plan to deliver an effective and safe survey facility to ESO is being maintained.

The United States Air Force Academy in Colorado Springs has obtained a 4m-diameter, lightweight telescope from the Space Based Laser project. Originally designed and constructed for space, this segmented telescope is being reconfigured for use as a ground-based facility - the largest in the world, wholly owned by any single college. The telescope comes fully equipped with both active and adaptive capabilities for segment phasing and wavefront correction. However, the optical design is a Mersenne configuration, and having been constructed for a space environment, it has an extremely thin (17mm) glass primary. We are redesigning the optics (with new secondary and tertiary mirrors) and are designing a mount and truss capable of both sidereal and low-Earth satellite tracking.

Lowell Observatory has initiated the development of a four meter class optical telescope with significant capabilities for solar system and broad spectrum astronomical research. Key to the Discovery Channel Telescope (DCT) is the ability to rapidly switch between 2 degree FOV imaging via a prime focus camera to 30 arc min FOV instrumentation at Ritchey-Chretien (RC) focus. The telescope is to be constructed at approximately 7700 feet altitude, Southeast of Flagstaff, Arizona at a site which has exhibited 0.6 arc sec best quartile seeing. The telescope will feature active optics and alignment capability and the Prime Focus Instrument will feature a Mosaic Focal Plane array of 40 2k x 4k CCDs. The RC instrument payload will be approximately 5000 lbs, allowing either large instruments or suites of co-mounted instruments. This telescope is being developed in partnership with Discovery Communications, Inc. (DCI), who will utilize the DCT and the association with Lowell Observatory to develop educational programming about astronomy and technology. The telescope will be a substantial enhancement to the current capabilities of Lowell Observatory.

Pan-STARRS, the Panoramic Survey Telescope and Rapid Response System, is a project to first develop a single wide field synoptic survey telescope (Pan-STARRS-1) followed by a system of four such telescopes. It is designed to accomplish many of the science goals envisioned by the decadal review for LSST. The primary mission of Pan-STARRS is the detection of potentially hazardous asteroids (PHA), secondary science objectives are a (nearly) all-sky survey, a medium-deep survey, an ultra-deep survey, and studies of transients and variable objects. This paper presents the current status of the telescope design, with emphasis on the optics.

The Liverpool Telescope is a 2.0 metre robotic telescope that is operating unattended at the Observatorio del Roque de Los Muchachos, Spain. This paper gives an overview of the design and implementation of the telescope and its instrumentation and presents a snapshot of the current performance during the commissioning process. Science observations are under way, and we give brief highlights from a number of programmes that have been enabled by the robotic nature of the telescope.

GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen and other national and international Partners. The refurbishment of the building is almost finished. The manufacturing of the telescope structure and the optics is still in progress. After the integration of the new complete retractable dome in July 2004 the telescope structure, optic and post focus instruments will be assembled during the rest of the year. First light is planned during May 2005.

The 8.4m Large Synoptic Survey Telescope (LSST) is a wide-field telescope facility that will add a qualitatively new capability in astronomy. For the first time, the LSST will provide time-lapse digital imaging of faint astronomical objects across the entire sky. The LSST has been identified as a national scientific priority by diverse national panels, including multiple National Academy of Sciences committees. This judgment is based upon the LSST's ability to address some of the most pressing open questions in astronomy and fundamental physics, while driving advances in data-intensive science and computing. The LSST will provide unprecedented 3-dimensional maps of the mass distribution in the Universe, in addition to the traditional images of luminous stars and galaxies. These mass maps can be used to better understand the nature of the newly discovered and utterly mysterious Dark Energy that is driving the accelerating expansion of the Universe. The LSST will also provide a comprehensive census of our solar system, including potentially hazardous asteroids as small as 100 meters in size. The LSST facility consists of three major subsystems: 1) the telescope, 2) the camera and 3) the data processing system. The baseline design for the LSST telescope is a 8.4m 3-mirror design with a 3.5 degree field of view resulting in an A-Omega product (etendue) of 302deg²m². The camera consists of 3-element transmisive corrector producing a 64cm diameter flat focal plane. This focal plane will be populated with roughly 3 billion 10μm pixels. The data processing system will include pipelines to monitor and assess the data quality, detect and classify transient events, and establish a large searchable object database. We report on the status of the designs for these three major LSST subsystems along with the overall project structure and management.

This paper reports a recently started project for a 2-m diameter robotic telescope dedicated to astronomy and education. After a brief recall of SAGAM-REOSC background in this domain, the project will be presented with more details on the telescope optics, mount and control system, the dome, the coating chamber and the weather station.

EOS Technologies has completed four 1.8m telescopes that are to be used in the NASA/JPL Interferometer. The 1.8m telescopes (Outriggers) will form the workhorse of the interferometric system. This paper presents some of the performance data obtained during the Telescope Factory Acceptance Tests showing some of the best telescope performance ever achieved with a telescope of this class.

SUNRISE is a balloon-borne solar telescope with an aperture of 1m, working in the UV/VIS optical domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35km at wavelengths around 220nm. Focal-plane instruments are a spectrograph/polarimeter, a Fabry-Perot filter magnetograph, and a filter imager. The first stratospheric long-duration balloon flight of SUNRISE over Antarctica is planned in winter 2006/2007. SUNRISE is a joint project of the Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofisica de Canarias, La Laguna, Tenerife. In this paper we will present an overview on the mission and give a description of the instrumentation, now, at the beginning of the hardware construction phase.

The Antarctica Plateau has recently turned out to be the best place on the Earth to perform astronomical infrared observations in the 2-20 um atmospheric windows and beyond, thanks to the extremely low sky background emission, the excellent atmospheric transparency and stability, the virtual absence of winds and the possibility of passively cooling the telescope and its focal plane instruments down to very low temperatures. Dome C, a site jointly exploited by Italian and French scientific teams in the framework of the Concordia project, lays on the Antarctica Plateau at an altitude of 3200m and presents exceptionally cold and dry climatic conditions. In this paper we shall describe the scientific motivations and the technical details of the infrared telescope IRAIT that we plan to put at Dome C starting from in 2005-2006. The IRAIT telescope is an alt-azimuth f/20 reflector, with a 0.8m parabolic primary mirror and a wobbling secondary mirror suitable for the specific techniques of IR observations. It will be equipped with a Near/Mid IR-camera built in Italy .

We present a summary of the Large Millimeter Telescope Project and its present status. The Large Millimeter Telescope (LMT) is a joint project of the University of Massachusetts (UMass) in the USA and the Instituto Nacional de Astrofisica, Optica y Electronica (INAOE) in Mexico to build a 50m-diameter millimeter-wave telescope. The LMT is being built at an altitude of 4600 m atop Volcan Sierra Negra, an extinct volcanic peak in the state of Puebla, Mexico, approximately 100 km east of the city of Puebla. Construction of the antenna is now well underway. The basic structure with a limited number of surface panels is expected to be completed in 2005. Engineering acceptance and telescope commissioning are expected to be completed in 2007.

ASTE (Atacama Submillimeter Telescope Experiment) is a project to install and operate a 10-m submillimeter telescope in the high altitude site (4,800 m) in Atacama desert, northern Chile. The project is aimed to explore the southern sky with submillimeter waves as well as to develop and evaluate various instruments and observing techniques. The telescope was shipped and re-assembled in Chilean site in early 2002, including the establishment of the on site infrastructure. Following evaluation of the telescope and receivers, scientific observations such as supernova remnants, galaxies, star forming regions and proto-planetary nebulae, have been carried out since early 2003. The high-precision 10-m antenna was measured to have the surface accuracy of 18.9 mm and the relative pointing accuracy was 1.2" r.m.s. for both azimuth and elevation. The subreflector is equipped with wobbling capability. Several types of receivers have been on board the telescope; the heterodyne-receivers operating at 100, 230, 345, 500 and 800 GHz bands including cartridge-type receivers, as well as a bolometer system covering 350, 650 and 850 GHz. The spectrometer is equipped with an XF type digital auto-correlator with four channels each covering up to 512 MHz with 1024 bins, which leads to 2 GHz coverage. The control system is designed to be capable of remote control from several sites via network connection, from the base facility at San Pedro de Atacama (2,400 m altitude) or even from Japan.

This contribution gives a description of the Sardinia Radio Telescope (SRT), a new general purpose, fully steerable antenna proposed by the Institute of Radio Astronomy (IRA) of the National Institute for Astrophysics. The radio telescope is under construction near Cagliari (Sardinia) and it will join the two existing antennas of Medicina (Bologna) and Noto (Siracusa) both operated by the IRA. With its large antenna size (64m diameter) and its active surface, SRT, capable of operations up to about 100GHz, will contribute significantly to VLBI networks and will represent a powerful single-dish radio telescope for many science fields. The radio telescope has a Gregorian optical configuration with a supplementary beam-waveguide (BWG), which provides additional focal points. The Gregorian surfaces are shaped to minimize the spill-over and the standing wave between secondary mirror and feed. After the start of the contract for the radio telescope structural and mechanical fabrication in 2003, in the present year the foundation construction will be completed. The schedule foresees the radio telescope inauguration in late 2006.

The Expanded Very Large Array project has the top-level goal of enhancing the performance of the Very Large Array by an order of magnitude or more in all areas: sensitivity, frequency coverge, spectral resolution, and spatial resolution. The project is being implemented in two, overlapping phases: Phase I, which began in 2000 and will finish by 2012 addresses all new capabilities except spatial resolution, and Phase II, which will improve tenfold the spatial resolution, and which is planned to begin in 2006, and finish by 2013. Progress in Phase I is very good, with first light and first fringes having been achieved, and tests of the new hardware and software now underway. A proposal for funding Phase II has now been delivered to the National Science Foundation. A critical component of the project is the new correlator, being designed and built by the Canadian Herzberg Institute of Astrophysics at the DRAO in Penticton, BC Canada. This new advanced correlator will be delivered beginning in late 2008. First shared-risk science with the early portions of the correlator will be done in late 2007.

The Discovery Channel Telescope (DCT) is a joint venture between Discovery Communications and Lowell Observatory. The telescope will have a 4.2-meter clear aperture, active primary mirror working at F/1.9. Two observing stations are presently planned; a Ritchey-Chretien focus some two meters behind the vertex of the primary mirror and a prime focus featuring a wide-field optical corrector (WFOC) with a two-degree field of view. The Ritchey-Chretien focus will be used for a variety of optical and near infrared imaging and spectroscopic instrumentation while the prime focus will be largely used as a survey tool to search for near-earth and Kuiper belt objects, for example. In order to take advantage of sub-arc second seeing at the DCT site, a stringent set of requirements has been placed on the two foci. The requirements are for the full-width, half-maximum (FWHM) image of a point source to be less than 0.20 arc second at the Ritchey-Chretien focus over a 21 arc minute field and less than 0.27 arc second at prime focus in each of six filter bands including a very broad band for survey purposes. This paper describes the optical design of the field correctors at the two foci. Particular attention is paid to the WFOC. This state of the art device poses a number of optical challenges which are discussed here, as well as mechanical challenges which are discussed elsewhere.

The Stratospheric Observatory For Infrared Astronomy (SOFIA) houses a 2.5-m infrared telescope in a Boeing 747SP aircraft. It will be operated at high altitudes above the atmospheric water vapor. The telescope is of Cassegrain type in a so-called Nasmyth configuration with a VIS and an IR focus. The 2.7-m primary mirror is a monolithic element of Zerodur with a milled honeycomb structure on the backside. Despite of its size, it has a high stiffness (approx. 160 Hz 1st natural frequency) and a mass of approx. 885 kg only. The mirror support structure is a lightweight structure made from CFRP panels and profiles, bonded and riveted together with metallic inserts and joints. The mirror mounting by dedicated flexures provides a very stiff but nevertheless isostatic mounting of the mirror in the support structure (first natural frequency around 70 Hz). The secondary mirror is made from SiC with a very high 1st natural frequency of approx. 2 kHz allowing noise-suppressing chopper operation without image distortions. The tertiary mirror assembly is implemented as a dichroic beam splitter providing the IR Nasmyth focus for the scientific instruments and as a fully reflective mirror providing the VIS Nasmyth focus for tracking purposes. The paper describes the optical system with its subassemblies, their tested as-built performance as well as the predicted extrapolated overall image performance. The integration of the primary mirror assembly into the aircraft will be shown. The further integration and alignment steps, planned for summer 2004, will be explained.

The Allen Telescope Array, originally called the One Hectare Telescope (1hT) [1] will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade.