and Other Particles
External Links page.
- Advantages: Atmospheric radio
frequency window; can observe day & night, in good or cloudy
- Sources of radio waves: Molecular
transitions; cold hydrogen; particles in magnetic fields.
- Telescopes: Must be very large
(see the 2-acre Green Bank, Jodrell Bank, and the 20-acre Arecibo
telescope!), and the resolution is still just a few arcminutes.
Unless several telescopes are connected and used together...
- Microwave astronomy: Telescopes
must be above most or all of the atmosphere, like the COBE satellite,
or the Boomerang balloon.
- General idea: Use several telescopes,
electronically connected together; greatly improves the resolution.
- Examples: The Very Large Array,
a 1-hectare telescope; or LOFAR, 350 km across, being built in the Netherlands
out of 15,000 small antennas.
- VLBI: Space-based or Earth-based
Very Long Baseline Interferometry; the resolution can be comparable
to reading a book in Tokyo from LA!!
- General idea: Can use telescopes
like those for visible light, but need different detectors, deployed
very high up.
- Infrared astronomy: Best from
mountains (like Mauna Kea), airplanes (like SOFIA scheduled for 2008),
or satellites (like NASA's Spitzer Space Telescope), and in the past
and ISO satellites; Why do these need to be cooled?
- Ultraviolet astronomy: Must
use rockets, balloons or satellites (like FUSE).
- X-ray astronomy: Need special
telescopes and electronic detectors on rockets, balloons or satellites;
Started with short rocket flights in the 1960's; Current examples
are the Chandra and XMM-Newton X-ray satellites.
- Gamma-ray astronomy: Also need
special detectors; Best above the atmosphere, like the satellites
HETE-2 and Integral [and the Compton Gamma-Ray Observatory, in
orbit until summer 2000], but there are several ground-based
and Other Particles
- Cosmic rays: Mostly charged
particles, in particular protons, coming from various sources;
The origin of the most energetic ones is unknown, but a large
array of detectors is being prepared to study them.
- Neutrino astronomy: Neutrinos
interact so little that detectors can be anywhere, and are best
where other particles can't go; see the ANTARES project.
The Next Window into the
Universe: Gravitational Waves
- What are they? Ripples in space
and time affecting lengths between objects; Predicted by Einstein's
theory of general relativity, and so far confirmed only by indirect
- How can we detect them? Using
(possibly large bars and) laser interferometers, like LIGO and
others, that became operational in 2002, and LISA, a future space-based
page by luca bombelli <bombelli at olemiss.edu>,
modified 29 sep 2012