Over most of the electromagnetic spectrum the earth's
atmosphere absorbs radiation emanating from extraterrestrial sources.
However, there is an atmospheric window
for wavelengths from 10 meters through 1 millimeter. Most radio telescopes
operate at the shorter wavelengths of less than 0.3 meters.
A relatively new field of astronomical observations is emerging for long
wavelength radio emissions with wavelengths greater than 1.0 meter. At these
long wavelengths, relatively low cost receiving stations can be built and
dispersed to many locations around the world.
With the use of inexpensive omni-directional antennas and receiving
stations, a phased array aperture synthesis telescope can be created. The
direction of observation ("beam") is chosen electronically by phase delays
between the antennas.
Multiple receiving stations outputs can be cross-correlated to greatly
improve the signal to noise ratio of the receiving system. With very long
base lines between stations, observations can be made emulating a telescope
with a size of the baseline, and with many stations combining their
outputs, an extremely sensitive astronomical observatory can be constructed.
Many astronomical objects emit radiation at long wavelengths, allowing the
following observations to be made:
- Observes the universe for a variety of physical artifacts from solar storms
- Detection of high-Z 21-cm Hydrogen
- Search for the Epoc of Reionization
- Whole sky observations
- Observing and detecting the galactic center and other bright radio objects
- Jupiter storms
- Solar storms
- Solar radio observations
- Ionospheric disturbances
- Dynamic universe
- Transient and variable sources
- Monitoring large portions of the sky
- Synoptic studies of galaxies and star forming regions
- Interstellar medium
- Cosmic magnetism
Current Long Wavelength Observatories
Over the last decade several long wavelength projects have been
funded and are underway.
- LWA - Located in central New Mexico, the
observatory will eventually harness the power of more than
13,000 antennas strategically placed in an area nearly 248 miles in
diameter. The antennas will provide sensitive, high-resolution
images of the sky. The new Long Wavelength Array (LWA) will operate
at wavelengths of 15 meters to 3.8 meters.
- LOFAR - Located in the European countries of
the Netherlands, Germany, Great Britain, France and Sweden, the
observatory will be based on an interferometric array of about 20,000 small antennas
operating at wavelengths of 30 meters to 1.25 meters.