The Crab Nebula is the aftermath of a star that exploded almost 1,000 years ago. The chronicles of medieval China contain a record of a supernova seen in July 1054 A.D., described as a "guest star," in this general position. At the time that it went supernova, the star could be seen in broad daylight for more than 20 days. The nebula is located about 6300 light years away. Calculations today confirm that a supernova at that distance would have shown as a beacon in the sky while it blazed with the light of about 400 million suns. The supernova would have had an absolute magnitude of about -17.
After the supernova exploded, the remains collapsed into a pulsar. In the 1940's, the Crab Nebula was identified as a strong source of radio waves. When the sky is examined with radio telescopes, the Crab Nebula is seen as one of the four brightest radio "stars" in the heavens. In April 1963, X-ray energy was detected from this region. In X-ray energy, the nebula region emits 100 times the energy emitted in the form of visible light. This pulsar, known as the Crab Pulsar, has the official designation PSR0531+21. The Crab Pulsar has collapsed to a remarkably small size, only about 10 miles in diameter. That compares to the size of the eye of a typical hurricane. However the matter comprising this stellar corpse is so dense, that a handful would weigh several million tons. The pulsar rotates or spins at the astonishing rate of 30 times a second. (Imagine if the Earth rotated at that rate. A day would last only about 17 milliseconds!)
This nebula is the most conspicious known supernova remnant in the heavens, and one of the brightest and nearest to us. Vast clouds of gas and dust have been flung out into space in expanding arcs and jets that now extend for light years. The gas in the nebula is expanding at the rate of 600 miles per second. At that velocity, the gas travels about 50 million miles per day. These remnants of what must have been a truely colossal explosion have now expanded to a diameter of about 6 light years. This gas appears as red filaments in this image. The actual density of the gas in the nebula is less than a trillionth the density of ordinary air. In addition, electrons originate from the pulsar remnant of the shattered star. The electrons travel at near light speeds in the presence of magnetic fields, and this causes the electrons to glow. This light from the electrons adds the soft glow filling the space between the red filaments shown in this image.
The Crab Nebula was discovered in 1731 by the English physician and amateur astronomer John Bevis. The nebula got its name from Lord Rosse in 1844, who described the filiments of gas extending through the nebula as resembling the legs of a crab. The nebula was independently discovered by Charles Messier 27 years after the discovery by Bevis, while Messier was looking for the comet of 1758. Messier was a comet hunter, and using less sophisticated and crude telescopes of the time, found that objects like the Crab Nebula were confusing and could be mistaken for comets. Thus, the Crab Nebula is notable in that it is the object that prompted Messier to produce his famous list of Messier objects. The idea behind the list was a catalogue of nebula and star clusters which would aid observers who might otherwise confuse the objects with comets, and thereby waste time observing a deep sky object that was not a comet. The Messier List, originally intended as a list of things to "avoid" in the sky by comet hunters in the 1700's, is now regarded as a list of the finest deep sky objects that an amateur astronomer can observe with a telescope or binoculars. As the first object in Messier's catalogue, the Crab Nebula has the distinction of being designated M1.
This is a color composite CCD image using data taken with the Schulman 32-inch telescope operated by Adam Block at the Mount Lemmon SkyCenter.
M1 (NGC 1952)
Constellation: Taurus
RA: 05h 34m 31.9s Dec: +22d 00' 52"
(J2000)
November 21, 23 & 25, 2012 and December
4 & 5, 2012
Images by Sid Leach, Dr. Francisco Arabia
& Adam Block
Scottsdale, Arizona
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