Telescopes and the Atmosphere

Transcription

1 Telescopes and the Atmosphere Our goals for learning How does Earth s atmosphere affect ground-based observations? Why do we put telescopes into space?

2 How does Earth s atmosphere affect ground-based observations? The best sites for astronomical observing are those that avoid the worst problems caused by the atmosphere. Light pollution Turbulence atmospheric losses (clouds, wavelength absorptions)

3 1) Light Pollution Scattering of human-made light in the atmosphere is a growing problem for astronomy

4 2) Twinkling and Turbulence Turbulent air flow in Earth s atmosphere distorts our view, causing stars to appear to twinkle Star viewed with groundbased telescope Same star viewed with Hubble Space Telescope

5 Adaptive Optics Rapidly changing the shape of a telescope s mirror compensates for some of the effects of turbulence

6 Adaptive Optics The light s wave peaks do not interfere with each other so badly, so the result is increased resolution Without adaptive optics With adaptive optics

7 The best ground-based sites for astronomical observing are Calm (not too windy) High (less atmosphere to see through) Dark (far from city lights) Dry (few cloudy nights)

8 Calm, High, Dark, Dry The best observing sites are atop remote mountains, in deserts Summit of Mauna Kea, Hawaii

9 3) Transmission in Atmosphere

10 3) Transmission in Atmosphere Only radio and visible light pass easily through Earth s atmosphere We need telescopes in space to observe other forms

11 What have learned? How does Earth s atmosphere affect ground-based observations? Telescope sites are chosen to minimize the problems of light pollution, atmospheric turbulence, and bad weather. Why do we put telescopes into space? Forms of light other than radio and visible do not pass through Earth s atmosphere. Also, much sharper images are possible because there is no turbulence.

12 Thought Question A team of astronomers wants to build an x-ray telescope on a high mountain (10 km above sea level). Will this work? A., we already have telescopes like this B. it's the 1st of its kind C. No it's too hard to put telescopes on mountains D.No x rays don't penetrate the atmopshere

13 Eyes & Cameras: Everyday Light Sensors Our goals for learning How can we observe nonvisible light? How can multiple telescopes work together?

14 How can we observe nonvisible light? A standard satellite dish is essentially a telescope for observing radio waves

15 Radio Telescopes A radio telescope is like a giant mirror that reflects radio waves to a focus

16 How can multiple telescopes work together?

17 Interferometry Interferometery is a technique for linking two or more telescopes so that they have the angular resolution of a single large one

18 Interferometry Easiest to do with radio telescopes Very Large Array (VLA) Now becoming possible with infrared and visible-light telescopes

19 Allen Telescope Array, CA 48 radio linked telescopes, more are planned

20 Other wavelengths: IR, Microwave SOFIA Balloons, used for measuring Cosmic rays, CMB and nutrinos To detect other wavelengths, instruments need to be above most of the atmosphere.

21 Space telescopes and Spacecraft Clearer view (space telescopes) Closer view (spacecraft)

22 Other wavelengths: UV & IR GALEX Spitzer Infrared and ultraviolet-light telescopes operate like visible-light telescopes but need to be above atmosphere to see all IR and UV wavelengths

23 High Energy Telescopes X-ray and Gamma ray telescopes also need to be above the atmosphere Chandra (X-rays) Compton Observatory (Gamma rays)

24 Chandra X-Ray Telescope Focusing of X-rays requires special mirrors Mirrors are arranged to focus X-ray photons through grazing bounces off the surface

25 M51 in Multiple Wavelengths The data from different spacecraft can be combined to produce simultaneous multi-wavelength images X-rays, Chandra Visible, Hubble IR, Spitzer

26 1960s - Present: Spacecraft!

27 Exploration Strategy 1. Initial Reconnaissance - a) Earth-based Observation - b) Fly- by mission. 2. Exploration phase 3. Intensive Study - a) Planetary orbiter. - b) Surface landers. - a) rovers - b) sample return - c) manned exploration

28 Current Vital Statistics Reconnaissance Exploration Intensive Study Observation Fly-by Orbiter Lander/Pr Rover Sample Manned Return obe Mercury In flight Venus Moon Mars proposed Jupiter Saturn /Titan Uranus Neptune Pluto In flight

29 Spacecraft Each mission has identified goals appropriate to what we want to know about a specific world. The answers we want each require specific types of data. The spacecraft carries instruments tailored to take that data and send it back to Earth for analysis

30 Instrument Purpose Cameras (often in IR) Take pictures Spectrometers Remote chemical analysis Result Usefulness maps Discover what s on the surface Spectra Discover some of surface composition. Neutron detectors Neutron maps find near surface water Lander instrument package (various) Measure surface conditions Temps, wind speed, images Discover what s it like on the surface Sample return Discover what ground Age dating, Find the age & is made of chemical analysis composition of key areas of the world Radio/plasma Science packages Measures behavior of Dust distribution in Understand upper atm. & electrical fields a system ring systems Magnetometer Altimeter Doppler shift of spacecraft Measures Magnetic Magnetic map fields Measures heights Height map spacecraft movement Find high-mass in relation the planet areas causing extra gravity Data sets are combined to discover what the interior of the world is like.