|Quoted from SEDS:
Discovered 1731 by British amateur
astronomer John Bevis.
The Crab Nebula, Messier 1 (M1, NGC 1952), is the most famous and
conspicuous known supernova remnant, the expanding cloud of gas created
in the explosion of a star as supernova which was observed in the year
1054 AD. It shines as a nebula of magnitude 8.4 near the southern "horn"
of Taurus, the Bull.
was noted on July 4, 1054 A.D. by Chinese astronomers as a new or "guest
star," and was about four times brighter than Venus, or about mag -6.
According to the records, it was visible in daylight for 23 days, and
653 days to the naked eye in the night sky. It was probably also
recorded by Anasazi Indian artists (in present-day Arizona and New
Mexico), as findings in Navaho Canyon and White Mesa (both Arizona) as
well as in the Chaco Canyon National Park (New Mexico) indicate; there's
a review of the research on the
Chaco Canyon Anasazi art online. In addition, Ralph R. Robbins of
the University of Texas has found Mimbres Indian art from New Mexico,
possibly depicting the supernova.
The Supernova 1054 was also assigned the variable star designation CM
Tauri. It is one of few
observed supernovae in our
Milky Way Galaxy.
The nebulous remnant was discovered by
in 1731, who
added it to his sky atlas, Uranographia Britannica.
on August 28, 1758, when he was looking for comet Halley on its first
predicted return, and first thought it was a comet. Of course, he soon
recognized that it had no apparent proper motion, and
cataloged it on September 12, 1758. It was the discovery of this
object which caused Charles Messier to begin with the compilation of
catalog. It was also the discovery of this object, which closely
resembled a comet (1758 De la Nux, C/1758 K1) in his small refracting
telescope, which brought him to the idea to search for comets with
telescopes (see his
note). Messier acknowledged the prior, original discovery by Bevis
when he learned of it in a letter of June 10, 1771.
Although Messier's catalog was primarily compiled for preventing
confusion of these objects with comets, M1 was again confused with comet
Halley on the occasion of that comet's second predicted return in 1835.
This nebula was christened the "Crab Nebula" on the ground of a
by Lord Rosse about 1844. Of the early observers, Messier, Bode and
William Herschel correctly remarked that this nebula is not resolvable
into stars, but William Herschel thought that it was a stellar system
which should be resolvable by larger telescopes. John Herschel and Lord
Rosse erroneously thought it is "barely resolvable" into stars. They and
others, including Lassell in the 1850s, apparently mistook filamentary
structures as indication for resolvability.
Early spectroscopic observations, e.g. by Winlock, revealed the
gaseous nature of this object in the later 19th century. The first photo
of M1 was obtained in 1892 with a 20-inch telescope. First serious
investigations of its spectrum were performed in 1913-15 by
Slipher (Slipher 1915,
1916): He found that the spectral emission
lines were split. It was later recognized that the true reason for this
is Doppler shift, as parts of the nebula are approaching us (thus their
lines are blueshifted) and others receding from us (lines redshifted).
In 1919, Roscoe Frank Sanford (Sanford 1919)
found that the spectrum consists of two major contributions: First, a
reddish component which forms a chaotic web of bright filaments, which
has an emission line spectrum (including hydrogen lines) like that of
diffuse gaseous (or planetary) nebulae, and second a strong blueish
diffuse background which has a continuous spectrum.
Curtis, in his
of this object based on Lick Observatory photographs, tentatively
classified it as a planetary nebula (Curtis 1918),
a view which was disproved only in 1933; this mis-classification can
still be found in some much newer handbooks.
In 1921, C.O. Lampland of Lowell Observatory, when comparing
excellent photographs of the nebula obtained with their 42-inch
reflector, found notable motions and changes, also in brightness, of
individual components of the nebula, including dramatic changes of some
patches near the central pair of stars (Lampland
1921). The same year, J.C. Duncan of Mt. Wilson Observatory compared
photographic plates taken 11.5 years apart, and found that the Crab
Nebula was expanding at an average of about 0.2" per year; backtracing
of this motion showed that this expansion must have begun about 900
years ago (Duncan 1921). Also the same year,
Knut Lundmark noted the proximity of the nebula to the 1054 supernova (Lundmark
In 1942, based on investigations with the 100-inch Hooker telescope
on Mt. Wilson, Walter Baade computed a more acurate figure of 760 years
age from the expansion, which yields a starting date around 1180 (Baade
1942); later investigations improved this value to about 1140. The
actual 1054 occurrance of the supernova shows that the expansion must
have been accelerated.
The nebula consists of the material ejected in the supernova
explosion, which has been spread over a volume approximately 10 light
years in diameter, and is still expanding at the very high velocity of
about 1,800 km/sec. The notion of gaseous filaments and a continuum
background was photographically confirmed by Walter Baade and Rudolph
Minkowski in 1930: The filaments are apparently the remnants from the
former outer layers of the former star (the "pre-supernova" or supernova
"progenitor"), while the inner, blueish nebula emits continuous light
highly polarised so-called synchrotron radiation, which is
emitted by high-energy (fast moving) electrons in a strong magnetic
field. This explanation was first proposed by the Soviet astronomer
J. Shklovsky (1953) and supported by
observations of Jan H. Oort and T. Walraven (1956).
Synchrotron radiation is also apparent in other "explosive" processes
in the cosmos, e.g. in the active core of the irregular galaxy
M82 and the
peculiar jet of giant elliptical galaxy
striking properties of the Crab Nebula in the visible light are equally
conspicuous in the
of the Anglo Australian Observatory,
and in Paul Scowen's
on Mt. Palomar.
In 1949, the Crab nebula was identified as a strong source of radio
radiation (Bolton et.al. 1949),
discovered 1948 named and listed as Taurus A (Bolton
1948), and later as 3C 144. X-rays from this object were detected in
April 1963 with a high-altitude rocket of type Aerobee with an X-ray
detector developed at the Naval Research Laboratory; the X-ray source
was named Taurus X-1. Measurements during lunar occultations of the Crab
Nebula on July 5, 1964, and repeated in 1974 and 1975, demonstrated that
the X-rays come from a region at least 2 arc minutes in size, and the
energy emitted in X-rays by the Crab nebula is about 100 times more than
that emitted in the visual light. Nevertheless, even the luminosity of
the nebula in the visible light is enormous: At its distance of 6,300
light years (which is quite well-determined, by
Virginia Trimble (1973)), its apparent brightness corresponds to an
absolute magnitude of about -3.2, or more than 1000 solar luminosities.
Its overall luminosity in all spectral ranges was estimated at 100,000
solar luminosities or 5*10^38 erg/s !
On November 9, 1968, a pulsating radio source, the Crab Pulsar (also
cataloged as NP0532, "NP" for NRAO Pulsar, or PSR 0531+21), was detected
in M1 by astronomers of the Arecibo Observatory 300-meter radio
telescope in Puerto Rico. This star is the right (south-western) one of
the pair visible near the center of the nebula in our photo. This pulsar
was the first one which was also verified in the optical part of the
spectrum, when W.J. Cocke, M.J. Disney and D.J. Taylor of Steward
Observatory, Tucson, Arizona found it flashing at the same period of
33.085 milliseconds as the radio pulsar with the 90-cm (36-inch)
telescope on Kitt peak; this discovery happened on January 15, 1969 at
9:30 pm local time (January 16, 1969, 3:30 UT, according to Simon
Mitton). This optical pulsar is sometimes also referred to by the
supernova's variable star designation, CM Tauri.
Only in 2007, it came to light that months before the detection of
the Crab Pulsar - end even the first pulsar ever discovered - this
object had been found in summer 1967, by US Air Force officer Charles
Schisler on duty. Charles was on radar duty at Clear USAFB Alaska in
summer 1967, when he noticed and logged a fluctuating radio source which
was not moving, i.e. at fixed RA and Dec. The next day it was there
again, and when he determined its position, he identified it with the
Crab Nebula. Subsequently, he found a number of further pulsars.
However, USAF decided that this was not their business, and didn't
publish his findings. Therefore, Joycelyn Bell independently found her
first pulsar a couple of months later.
It has now been established that this pulsar is a rapidly rotating
neutron star: It rotates about 30 times per second! This period is very
well investigated because the neutron star emits pulses in virtually
every part of the electromagnetic spectrum, from a "hot spot" on its
surface. The neutron star is an extremely dense object, denser than an
atomic nucleus, concentrating more than one solar mass in a volume of 30
kilometers across. Its rotation is slowly decelerating by magnetic
interaction with the nebula; this is now a major energy source which
makes the nebula shining; as stated above, this energy source is 100,000
times more energetic than our sun.
In the visible light, the pulsar is of 16th apparent magnitude. This
means that this very small star is roughly of absolute magnitude +4.5,
or about the same luminosity as our sun in the visible part of the
Jeff Hester and
Paul Scowen have used the
Crab Nebula M1 (see also e.g. Sky & Telescope of January,
1995, p. 40). Their continuous investigations with the HST have provided
new insight into the
changes of the Crab nebula and pulsar. More recently,
the Heart of the
Crab was investigated by HST astronomers.
This object has attracted so much interest that it was remarked that
astronomers can be devided into two fractions of about same size: Those
who do work related to the Crab nebula, and those who don't. There was a
"Crab Nebula Symposium" in Flagstaff, Arizona in June, 1969 (see PASP
Vol. 82, May 1970 for results - Burnham). The IAU symposium No. 46, held
at Jodrell Bank (England) in August 1970 was solely devoted to this
object. Simon Mitton has written a nice
book on the Crab Nebula M1 in 1978, which is still most readable and
informative (it is also source for some of the informations here).
The Crab Nebula can be found quite easily from Zeta Tauri (or 123
Tauri), the "Southern Horn" of the Bull, a 3rd-magnitude star which can
be easily found ENE of Aldebaran (Alpha Tauri). M1 is about 1 deg N and
1 deg W of Zeta, just slightly south and about 1/2 degree west of a
mag-6 star, Struve 742.
The nebula can be easily seen under clear dark skies, but can equally
easily get lost in the background illumination under less favorable
conditions. M1 is just visible as a dim patch in 7x50 or 10x50
binoculars. With a little more magnification, it is seen as a nebulous
oval patch, surrounded by haze. In telescopes starting with 4-inch
aperture, some detail in its shape becomes apparent, with some
suggestion of mottled or streak structure in the inner part of the
nebula; John Mallas reports that under excellent conditions, an
experienced observer can see them throughout the inner portion of the
nebula. The amateur can verify Messier's impression that M1 looks indeed
similar to a faint comet without tail in smaller instruments. Only under
excellent conditions and with larger telescopes, starting at about 16
inches aperture, suggestions of the filaments and fine structure may
As the Crab Nebula is situated only 1 1/2 degrees from the ecliptic,
there are frequent conjunctions and occasional transits of planets, as
well as occultations by the Moon (some of them mentioned above).
M1 is situated in a nice Milky Way field. The star Zeta Tauri is
remarkable as it is a Gamma Cassiopeiae type variable, a rather rapidly
rotating star of spectral type B4 III pe which has ejected an expanding
gas shell, and has a fainter spectroscopic companion star in an orbit of
about 133 days period. Preceding M1 two minutes (or half a degree) in
Right Ascension is Struve 742 or ADS 4200, another visual binary star
with components A (mag 7.2, spectrum F8, of yellow color) and B (mag
7.8, white) separated by about 3.6" in position angle 272deg, and
orbiting each other in about 3000 years.
Observations and Descriptions of M1
and X-Ray images from the ASTRO-1 Space Shuttle mission (STS-35).
images from the ASTRO-1 mission.
Space Telescope images of M1 -
more HST images
- newer HST
X-ray Observatory images of M1
Multispectral image of M1 (X-ray: Chandra, optical: Hubble,
from ESO's VLT
images of M1
images of M1;
images of M1
the Crab Pulsar
Bill Arnett's M1
(G184.6-5.8) data from D.A. Green's Catalogue of Galactic
Crab Nebula Stuff
from the Chandra X-ray Observatory Team
A History of the Crab Nebula from the Space Telescope Science
Multispectral Image Collection of M1, SIRTF Multiwavelength Messier
Images of the Crab Pulsar (Michael Richmond and KPNO)
Jack Schmidling's Crab
data for M1
Publications on M1 (NASA ADS)
Observing Reports for M1 (IAAC Netastrocatalog)
NGC Online data
Reference and Further reading:
- Walter Baade, 1942. The Crab Nebula.
Astrophysical Journal, Vol. 96, p. 188-198 (September 1942)
- J.G. Bolton, 1948. Discrete Sources of
Galactic Radio Frequency Noise. Nature, Vol. 162, No. 4108, pp.
140-141 (July 24, 1948)
- J.G. Bolton, G.J. Stanley, and O.B. Slee,
1949. Positions of Three Discrete Sources of Galactic
Radio-Frequency Radiation. Nature, Vol. 164, No. 4159, pp. 101-102
(July 16, 1949)
- Heber D. Curtis, 1918. The Planetary
Nebulae. Publications of the Lick Observatory, No. 13, Part III, p.
55-74. Here fig. 11
- John Charles Duncan, 1921. Changes
Observed in the Crab Nebula in Taurus. Mt. Wilson Communications,
No. 76. Proceedings of the National Academy of Sciences of the
United States of America, Vol. 7, No. 6, pp. 179-180 (June 15, 1921)
- Carl Otto Lampland, 1921. Observed
Changes in the Structure of the "Crab" Nebula (N. G. C. 1952).
Publications of the Astronomical Society of the Pacific, Vol. 33,
No. 192, pp. 79-84 (April 1921)
- Knut Lundmark, 1921. Suspected New
Stars Recorded in Old Chronicles and Among Recent Meridian
Observations. Publications of the Astronomical Society of the
Pacific, Vol. 33, No. 195, pp. 225-238 (October 1921)
- N.U. Mayall and J.H. Oort, 1942.
Further Data Bearing on the Identification of the Crab Nebula with
the Supernova of 1054 A.D. Part II. The Astronomical Aspects.
Publications of the Astronomical Society of the Pacific, Vol. 54,
No. 318, p. 95-104 (04/1942)
- Jan H. Oort and T. Walraven, 1956.
Polarization and composition of the Crab nebula. Bulletin of the
Astronomical Institute of the Netherlands, Vol. 12, p. 285
Also: Polarization and the radiating mechanism of the Crab nebula.
Radio astronomy, Proceedings from 4th IAU Symposium. International
Astronomical Union. Symposium no. 4, Edited by Hendrik Christoffel
Van de Hulst. Cambridge University Press, p. 197-200 (1957)
- R.F. Sanford, 1919. Spectrum of the
Crab Nebula. Publications of the Astronomical Society of the
Pacific, Vol. 31, No. 180, pp. 108-109 (April 1919)
- Josif Samuilovic Shklovsky, 1953.
Dokl. Akad. NAUKL SSSR (Proc. Acad. Sci. U.S.S.R.), 90, 983.
- Vesto M. Slipher, 1915. Nature, Vol.
95, p. 185
- Vesto M. Slipher, 1916. Spectrographic
Observations of Nebulae and Star Clusters. Publications of the
Astronomical Society of the Pacific, Vol. 28, pp. 191-192
- Virginia Trimble, 1973. The Distance
to the Crab Nebula and NP 0532. Publications of the Astronomical
Society of the Pacific, Vol. 85, No. 507, p. 579-585 (10/1973)