Non-Visible Radiation
and Other Particles
External Links page.

  Radio Astronomy

  • Advantages: Atmospheric radio frequency window; can observe day & night, in good or cloudy weather.
  • 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.

Radio Interferometry

  • 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!!

  Infrared and Ultraviolet Astronomy

  • 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 the IRAS and ISO satellites; Why do these need to be cooled?
  • Ultraviolet astronomy: Must use rockets, balloons or satellites (like FUSE).

High-Energy Radiation

  • 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 projects.

  Cosmic Rays 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 means.
  • 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 interferometer.

page by luca bombelli <bombelli at>, modified 29 sep 2012