updated: Jan 11, 2013, 9:23 AM
By Chuck McPartlin
The Ring Nebula was an example of the old age of a low-mass star
like our Sun. The Crab Nebula is the debris of the explosive death
via core-collapse supernova of a star with a mass estimated to have
been 5 to 8 solar masses. Such stars live fast and die young,
expending their nuclear fuel in millions of years, instead of billions.
The supernova which produced the Crab Nebula on July 4, 1054 was
observed and recorded by people in China, Japan, India, and Arabia.
It was so bright that it was visible in daylight for over three weeks,
and remained visible by eyeball at night for almost two years.
Chinese astronomers called it a Guest Star.
The debris cloud forming the Crab Nebula is estimated to be 6300
light years away, and has expanded to about 6 light years across and
13 light years long. It is dimly visible in amateur telescopes near
the tip of the eastern horn of the constellation Taurus, the Bull.
This image was made with a color video camera that's very sensitive,
but with only normal TV resolution. It is an integration of 56 seconds,
with a lot of signal noise. It has been heavily processed in an
attempt to bring out some details in the cloud. Please don't show it
to any real astrophotographers.
The Crab Nebula got its name as the result of a drawing made from
observations with the largest telescope in the world in the 1840s,
showing some of the brighter tendrils visible in this image, which
resembled crab legs. If you're traveling to Ireland, you can visit
Birr Castle and see this telescope, still used for public viewing.
If you don't want to go that far, you can come to one of the second
Saturday of the month public star parties at the Santa Barbara Museum
of Natural History, or one of the other Astronomy events listed on the
Edhat Events page. That's this Saturday, weather permitting. Dress warmly!
Radio astronomers in the 1960s detected dozens of objects that emitted
very regular beeps of radio energy, accurately repeating down to
nanosecond time scales. This worried them, and they called them LGM
objects, for Little Green Men, because they thought these were artificial
beacons. Theoretical astrophysicists recognized them as pulsars - neutron
stars with intense magnetic fields, spinning rapidly.
At the center of the Crab Nebula is the Crab Pulsar, the crushed core of
the exploded star. It's estimated to be about 15 miles across, and
contains about 1.5 solar masses. It's rotating at a rate of 30.2 times a
second, beaming radio energy out of its magnetic poles, which don't
coincide with its rotational axis - a dense and rapid cosmic lighthouse.
References for a cloudy night:
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