5.1 optical observatories 5.1 a: observatory sites: one limitation: the time needed for optics to...
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5.1 Optical Observatories5.1 a: Observatory Sites:
One limitation: the time needed for optics to reach equilibrium shape when exposed to severe temperatures.
Southern Hemisphere.DryHighDarkSteady atmosphere.Adaptive optics modify the shape of the mirror
to cancel the blurring effects of the atmosphere.
5.1 Optical Observatories5.1 b: The new Generation of Optical
TelescopesTwin 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 Telescopes5.2 a: Schmidt TelescopesCombines 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 Telescopes5.2 b: The Forthcoming Large Survey
TelescopeLSST6.5 m mirrorSurveys the whole sky every week.Data will be available on the internet.
5.3 Hubble Space Telescope (HST)2.4 m mirrorLaunched in 19902 billion $ cost559 km orbit above EarthMaintenance trip every 3 years3 advantages:
Above Earth’s atmosphere, resolution only limited by mirror size (0.1 arc sec).
HST can detect fainter objects, darknessUV & IR are detectable.
HTS facts Launch date April 24, 1990, 8:33:51 am Launch vehicle Space Shuttle Discovery Mission length 20 years, 7 months Mass 11,110 kg Type of orbit Near-circular low Earth orbit Orbit height 559 km (347 mi) Orbit period 96–97 minutes (14-15 periods per day) Orbit velocity 7,500 m/s Acceleration gravity 8.169 m/s2 Wavelength Optical, ultraviolet, near-infrared Diameter 2.4 m Collecting area 4.5 m2 Focal length 57.6 m
HST Maintenance missionsDec 1993Feb 1997Dec 1999Mar 2002May 2008Retirement 2011
List of Space Telescopeshttp://en.wikipedia.org/wiki/
List_of_space_telescopes
5.3 a: The Next Generation Space Telescope
NGSTPlanned 8-m mirrorReduced 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 PointsLagrange 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. http://www.esa.int/esaSC/SEMM17XJD1E_index_0.html
http://www.astro.uwo.ca/~wiegert/etrojans/etrojans.html
5.4 Recording the Data1- 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 pixelHST has 800 x 800 pixels array
5.6 Observing at Short WavelengthsOrdinary films can be usedHST 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 EarthHST observes at IR
5.7 Observing at Long Wavelengths
Radio Astronomy
Arecibo Radio Telescope
Location Arecibo, Puerto Rico
Built 1963Telescope style spherical reflector
Diameter 305 m (1,001 ft)
Collecting area 73,000 square metres
Focal length 265.109 m
Radio TelescopesRadio waves cause electrical changes in antennas.
Large dishes are needed for 2 reasons:Larger surface area more sensitiveLarger dish better resolution
Radio Telescopes1-m optical telescope is 2 million wavelengths
across100-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