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Multiwavelength Milky Way Definitions

Angular resolution is a measure of the angular size of the smallest object that can be distinguished by a telescope.

The angular diameter is the angle that is subtended by the diameter of an object.

COBE - The Cosmic Background Explorer. To learn more, go to the COBE Home page.

False color image - An image in which 1) colors are used to visualize light that our eyes cannot see, or 2) colors are used that are different than what our eyes would normally see. Go to Making an Image for more information.

Galactic coordinates are like the longitude and latitude system we use for the earth. Galactice latitude is measured from the galactic plane (Earth latitude is measured from the equator), and galactic logitude is measured from the direction to the galactic center (Earth longitude is measured from London's Greenwich Observatory). Go to Using the Multiwavelength Maps for more information.

The galactic plane is the disk of the galaxy, which is about 25 kilo-parsecs (kpc) in diameter and 0.6 kpc thick.

IRAS - The Infrared Astronomical Satellite. The Astrophysics Data Facility has a brief introduction about IRAS.

A light year (ly) is the distance it takes light to travel in one year. Astronomers decided to come up with a unit of length to better express the great distances that are encountered in astronomy. One light year is equal to 9.46 x 1012 km, or just around 6 trillion miles!

A parsec is a unit of distance. One parsec is equal to 3.09 x 1013 km, or 3.26 light years.

A resolution element is the depiction of the smallest object resolved by the instrument, scaled to the image size.

An Sbc galaxy is a spiral galaxy whose classification falls somewhere between "Sb" and "Sc". Spiral galaxies are characterized by bulges and spiral arms, and are often classified by how these structures appear. On one end of the classification scale are spiral galaxies with large central bulges and tightly wound spiral arms. These are called "Sa" galaxies ("S" for "spiral"). On the other end of the scale are spiral galaxies with small central bulges and loosely wound spiral arms. These are designated "Sc" galaxies. "Sb" galaxies have a moderate-sized central bulge, and their spiral arms are moderately wound around it.

The 21-centimeter transition of hydrogen refers to an atomic process. Electrons and protons have angular momentum (spin). The single electron and proton of a hydrogen atom can either spin in the same direction or in opposite directions. When the electon flips from one direction to the other, the hydrogen atom gains or loses a small amount of energy which has a wavelength of 21 centimeters.