5.1 Optical Observatories 5.1 a: Observatory Sites: One limitation: the time needed for optics to reach equilibrium shape when exposed to severe temperatures. Southern Hemisphere. Dry High Dark Steady atmosphere. Adaptive optics modify the shape of the mirror to cancel the blurring effects of the atmosphere.

5.1 Optical Observatories 5.1 b: The new Generation of Optical Telescopes Twin Keck telescopes (10 m each), mirror made of many smaller segments. Four 8-m telescopes (Very Large Telescope VLA) in Chile. With segmented mirrors, there is no limit on size 30-m plan (California) 100-m plan European Southern Observatory.

5.2 Wide-Field Telescopes 5.2 a: Schmidt Telescopes Combines the best features of reflector with that of refractor. Spherical large mirror. Thin lens (correcting plate) FOV 7 deg. Instead of 2 arc min for the 5-m telescope.

5.2 Wide-Field Telescopes 5.2 b: The Forthcoming Large Survey Telescope LSST 6.5 m mirror Surveys the whole sky every week. Data will be available on the internet.

5.3 Hubble Space Telescope (HST) 2.4 m mirror Launched in billion $ cost 559 km orbit above Earth Maintenance trip every 3 years 3 advantages: Above Earth’s atmosphere, resolution only limited by mirror size (0.1 arc sec). HST can detect fainter objects, darkness UV & IR are detectable.

HTS facts Launch dateApril 24, 1990, 8:33:51 am Launch vehicleSpace Shuttle Discovery Mission length20 years, 7 months Mass11,110 kg Type of orbitNear-circular low Earth orbit Orbit height559 km (347 mi) Orbit period96–97 minutes (14-15 periods per day) Orbit velocity7,500 m/s Acceleration gravity8.169 m/s 2 WavelengthOptical, ultraviolet, near-infrared Diameter2.4 m Collecting area4.5 m 2 Focal length57.6 m

HST Maintenance missions Dec 1993 Feb 1997 Dec 1999 Mar 2002 May 2008 Retirement 2011

List of Space Telescopes

5.3 a: The Next Generation Space Telescope NGST Planned 8-m mirror Reduced to 6-m mirror (better, cheaper, faster) It would go to one of Lagrangian points. There, it will not go through day & night cycles. It will be able to observe for a longer fraction of time.

Lagrange Points Lagrange points are locations in space where gravitational forces and the orbital motion of a body balance each other. There are five Lagrangian points in the Sun-Earth system and such points also exist in the Earth-Moon system. ml ml

5.4 Recording the Data 1- Films (silver emulsion – chemical reaction – negative) 2- Electronic devices (Photometry) 3- CCD charge-coupled device: when light hits the surface of the chip, electrons are released. Discrete area of a chip is called pixel HST has 800 x 800 pixels array

5.6 Observing at Short Wavelengths Ordinary films can be used HST is the largest for UV observation X rays pass through mirrors ? X rays can still bounce off a surface if they strike at very low angel (Grazing Incidence).

IR image of Earth HST observes at IR 5.7 Observing at Long Wavelengths

Radio Astronomy Arecibo Radio Telescope Location Arecibo, Puerto Rico Built1963 Telescope stylespherical reflector Diameter305 m (1,001 ft) Collecting area 73,000 square metres Focal length m

Radio Telescopes Radio waves cause electrical changes in antennas. Large dishes are needed for 2 reasons: Larger surface area  more sensitive Larger dish  better resolution

Radio Telescopes 1-m optical telescope is 2 million wavelengths across 100-m radio telescope is 1000 wavelengths across if used to detect radio waves 10 cm in wavelength. Radio telescopes used to study millimeter length radio waves do not have to be as physically large as telescopes meant to study longer wavelengths.

Phases of the Moon