Monday March 22nd 1999
Announcements:

Lecture notes:
Class 29.
"More than meets the eye"

In the last class we covered optical telescopes.  Today we'll move on to talk about telescopes at other wavelengths.

Photons at all different wavelengths are constantly impinging on Earth - we would miss huge amounts of information if we only used visual light to study universe.

Slides shown - of different views from optical radio infrared and near infrared.

COBE satellite - here can see cool low mass stars - like K and M stars which are cool enough to radiate down there.

Gamma ray slide - most of gamma rays from our Galaxy were made when energetic charged particles slamed into gas clouds.  At high Galactic latitudes see several active galactic nuclei (AGN)

Radio Telescopes
Going back to our plot of the electromagnetic spectrum we see that the other main range of wavelengths where astronomy from ground will work is radio.

As a result there are literally hundreds of radio telescopes that have been built all around the world.

These are not made from glass mirrors or lenses but rather are radio dishes kind of like those used for TV signals.

Focus radio waves into an antenna - amplified - computer.  Largest is 300 M in Arecibo dish in Puerto Rico.

A particularly neat trick is that radio astronomers have developed ways to combine the signals from 2 or more radio
telescopes to effectively create a huge radio telescope as big as dish separation - gives great spatial resolution.

Example is the Very Large Array in New Mexico - 27 radio telescopes that can simulate a huge one 40 km in diameter.

Even more dramatic is VLBI and space VLBI - big as Earth or bigger.

Slides shown of radio telescopes and sun in radio.

Space astronomy - to study universe at other wavelengths we need to be above our atmosphere - limitations are expensive and hard to repair satellites.

Most famous space observatory is Hubble Space Telescope.

Works in optical UV and IR.  Launched in 1990.  No "seeing" problems because above atmosphere so great  resolution of less than 0.1 arcsecond.  Has 2.4 M mirror.  Relatively small light gathering power.

I've already shown many HST pictures as part of this class and many more can be found at the Astro 1 WWW page.

Another type of space astronomy is X-ray astronomy - people have now launched about 20 X-ray satellites and more are planned.

X-rays let us home in on some of the most violent and high temperature regions in the Universe.

Gas falling onto black holes.  1x10⁶ K to 1x10⁹ K gas near black holes.
Gas crashing into surface of neutron star at about 1/3 c at about 1x10⁷ K
hot gas in the remnant of a supernova at 1E6K
hot gas in the coronae of some stars - 1E6
Hot gas between the galaxies in a galaxy cluster.

X-ray slides.
Uhuru = first X-ray satellite
Einstein - first imaging in X-rays
3C273 - black hole in AGN
M31 - many neutron stars black holes
Tycho SNR - exploded star remnant
NGC253 - collective supernovae.
Virgo cluster - intracluster gas.

Chandra X-Ray Observatory is coming.  Can see on WWW page