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 TurbulenceTurbulent 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 OpticsRapidly changing the shape of a telescope’s mirror

compensates for some of the effects of turbulence

Adaptive OpticsThe light’s wave peaks do not interfere with each

other so badly, so the result is increased resolution

Without adaptive optics With 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

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 thisB.Yes it's the 1st of its kindC. No it's too hard to put telescopes on mountainsD.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.

SOFIA Balloons, 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

GALEX Spitzer

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, Chandra Visible, Hubble IR, Spitzer

M51 in Multiple WavelengthsThe 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

Observation Fly-by Orbiter Lander/Probe

Rover Sample Return

Manned

Mercury Yes Yes Yes In flight

Venus Yes Yes Yes YesMoon Yes Yes Yes Yes Yes Yes YesMars Yes Yes Yes Yes Yes proposed

Jupiter Yes Yes Yes YesSaturn Yes Yes Yes Yes/Titan

Uranus Yes YesNeptune Yes 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

Instrument Purpose Result UsefulnessCameras

(often in IR)Take pictures maps Discover what’s on the

surface

Spectrometers Remote chemical analysis

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 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

Magnetometer Measures Magnetic fields

Magnetic map Data sets are combined to discover what the interior of the world is like.Altimeter Measures heights Height map

Doppler shift of spacecraft

spacecraft movement in relation the planet

Find high-mass areas causing extra gravity