Why look at differentfrequencies of light?

• Cooler objects are only visible at long wavelengths: radio, microwaves, IR.

• Hotter objects are only visible at short wavelengths: UV, X-rays, -rays.

Radio Telescopes

• Detects cool gases: H+ H H2

• Can detect molecules out in space:• oxygen O2

• carbon dioxide CO2

• hydrogen cyanide HCN• formaldehyde H2CO

• Ethanol CH3COOH

Advantages / Problems

• Operates night or day• Atmosphere doesn’t absorb radio waves

• Poorest resolution of any type of light (doesn’t see details well)

• Solution is to make antennas (dishes) VERY large

Arecibo Radio Telescope, Arecibo, Puerto Rico

Puerto Rico

GreenBankTelescope

Green Bank,W.Va.

The dishwould holdFulton Field

Radio Interferometry – a Recipe

• Take 2 (or more) widely separated radio telescopes…

• Electronically blend their signals…• Result is as if you had a telescope with a

diameter equal to the distance between the two separate telescopes.

• VASTLY improves resolution!

Very Large Baseline Array sites across the US. Together thesetelescopes form a huge interferometer.

Infrared (IR) Telescopes• Very similar to visible wavelength

telescopes, except for the detector, called a bolometer.

• IR scopes detect heat from warm gas or warm objects. “Warm” means not hot enough to glow in visible light.

• These scopes must be kept very cold or the heat the scope itself radiates swamps out what they’re looking for.

What kinds of objects?

• IR telescopes “see” warm gas, molecules & dust. In some cases, they can look through cooler dust to see what’s inside the dust clouds!

• Since stars form where there’s lots of dust, these scopes are great for looking inside dusty nebulas where new stars form.

We can’t see everything just invisible wavelengths !!

ISO – theInfraredSpaceObservatory

EuropeanSpaceAgency (ESA)

Orbital Telescopes

• Why put a telescope in orbit?• Gets it above the atmosphere with all its

dust, ozone, water vapor, and CO2 that absorb so much of what we want to see.

• What’s the most famous orbiting telescope?

If you said the Hubble Space Telescopeor HST, you’re right!

HST does detect visible light

• It also detects ultraviolet light.• 2.4 meter mirror = 230,400 eyes!• Resolution is 0.0126 arcsecond or

1 / 3,500,000th of a circle.• We’re used to seeing photos like these!

X-ray & Gamma Telescopes

• “Sees” very hot objects:• Black Holes• Pulsars & Neutron Stars• Supernovas

• VERY good resolution – sees fine details

NGC 4261 – a huge black holeat the center of a distant galaxy

A supernova – an exploding star

What’s left after the explosion – a supernova remnant.

This one’s called Cassiopeia A.

The Crab Nebula in visible light (left) & X-rays (right).

At the center of the Crab Nebula – a PULSAR