5.1 optical observatories 5.1 a: observatory sites: one limitation: the time needed for optics to...

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