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

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)

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

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

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

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

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)

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

3) Transmission in Atmosphere

Only radio and visible light pass easily through Earth’s atmosphere We need telescopes in space to observe other forms

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.

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

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

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

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

How can multiple telescopes work together?

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

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

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

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

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

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

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

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

X-rays, ChandraVisible, HubbleIR, Spitzer M51 in Multiple Wavelengths The data from different spacecraft can be combined to produce simultaneous multi-wavelength images

1960s - Present: Spacecraft!

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

Current Vital Statistics Reconnaissance Exploration Intensive Study ObservationFly-byOrbiterLander/ Probe Rover Sample Return Manned Mercury Yes In flight Venus Yes Moon Yes Mars Yes proposed Jupiter Yes Saturn Yes Yes/Titan Uranus Yes Neptune Yes Pluto Yes In flight

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

InstrumentPurposeResultUsefulness Cameras (often in IR) Take picturesmapsDiscover what’s on the surface SpectrometersRemote chemical analysis SpectraDiscover some of surface composition. Neutron detectors” Neutron mapsfind near surface water Lander instrument package (various) Measure surface conditions Temps, wind speed, images Discover what’s it like on the surface Sample returnDiscover what ground is made of Age dating, chemical analysis Find the age & composition of key areas of the world Radio/plasma Science packages Measures behavior of electrical fields Dust distribution in a system Understand upper atm. & ring systems MagnetometerMeasures Magnetic fields Magnetic mapData sets are combined to discover what the interior of the world is like. AltimeterMeasures heightsHeight map Doppler shift of spacecraft spacecraft movement in relation the planet Find high-mass areas causing extra gravity