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Chandra's unusual orbit was achieved after deployment by a built-in propulsion system which boosted the observatory to a high Earth orbit. This orbit, which has the shape of an ellipse, takes the spacecraft more than a third of the way to the moon before returning to its closest approach to the Earth of 9,942 miles. More

A new form of radiation was discovered in 1895 by Wilhelm Roentgen, a German physicist. He called it X-radiation to denote its unknown nature. This mysterious radiation had the ability to pass through many materials that absorb visible light. X-rays also have the ability to knock electrons loose from atoms. Over the years these exceptional properties have made X-rays useful in many fields, such as medicine and research into the nature of the atom.

Eventually, X-rays were found to be another form of light. Light is the by-product of the constant jiggling, vibrating, hurly-burly of all matter. More

The word light usually makes one think of the colors of the rainbow or light from the Sun or a lamp. This light, however, is only one type of electromagnetic radiation. Electromagnetic radiation comes in a range of energies, known as the electromagnetic spectrum. The spectrum consists of radiation such as gamma rays, x-rays, ultraviolet, visible, infrared and radio.

Electromagnetic radiation travels in waves, just like waves in an ocean. The energy of the radiation depends on the distance between the crests (the highest points) of the waves, or the wavelength. In general the smaller the wavelength, the higher the energy of the radiation. More

In astronomy, distances are measured in units of light years, where one light year is the distance that light travels in a year—10 trillion kilometers. For historical reasons having to do with measuring distances to nearby stars, professional astronomers use the unit of parsecs, with one parsec being equal to 3.26 light years. More

A supernova is the explosive death of a star, caused by the sudden onset of nuclear burning in a white dwarf star, or gravitational collapse of the core of massive star followed by a shock wave that disrupts the star.

Supernovas are some of the most dramatic events in the cosmos. These titanic events send shock waves rumbling through space and create giant bubbles of gas that have been superheated to millions of degrees. Chandra has captured supernovas and the remnants they've left behind in spectacular X-ray images, helping to determine the energy, composition, and dynamics of these celestial explosions.  More

Dark matter is a term used to describe matter that can be inferred to exist from its gravitational effects, but does not emit or absorb detectable amounts of light.

The nature of dark matter is unknown. A substantial body of evidence indicates that it cannot be baryonic matter, i.e., protons and neutrons. The favored model is that dark matter is mostly composed of exotic particles formed when the universe was a fraction of a second old. Such particles, which would require an extension of the so-called Standard Model of elementary particle physics, could be WIMPs (weakly interacting massive particles), or axions, or sterile neutrinos.  More

Dark energy is a hypothetical form of energy that permeates all space and exerts a negative pressure that causes the universe to expand at an ever-increasing rate.

At the close of the 20th century, our perception of the Universe was jolted. Instead of slowing down after the Big Bang, the expansion of the Universe was found to be accelerating. Was the cosmic acceleration due to Einstein's cosmological constant, a mysterious form of "dark energy," or perhaps a lack of understanding of gravity? The answer is still out there. By studying clusters of galaxies, X-ray astronomy is tackling this question using powerful techniques that are independent of other methods currently being employed or proposed for the future.  More