Download Orion

Constellation: Orion
Designation
Proper
Name
(alpha)
(beta)
(gamma)
(delta)
(epsilon)
(zeta)
Betelgeuse
Rigel
Bellatrix
Mintaka
Alnilam
Alnitak
Apparent
Magnitude
m
+0.45
+0.34
+1.64
+2.20
1.70
1.79
Which star is hottest?
Absolute
Magnitude
M
-5.04
-7.1
-4.2
-5.9
-6.8
-6.6
Distance
lyrs
427
773
470
1500
1600
1600
Spectral Type
Luminosity
Class
M2 I
B8 I
B2 III
O9 II
B0 I
O9 I
Single or
Multiple
Star System
Single
Binary
Single
Eclip. Binary
Single
Triple
Coolest?
Which star appears brightest?
Which star is the most luminous?
Dimmest?
Least luminous?
Why does Mintaka appear so dim given that it is very luminous?
Which stars are main sequence stars?
Rigel is a true supergiant, blazing white-hot star of intense brilliance and dazzling beauty. Its surface temperature is
about 12,000 K and its energy output exceeds that of our Sun by a factor of many thousands; the computed
luminosity is something like 57,000 times the brightness of our Sun. Rigel is thus one of the most luminous objects
known in our Galaxy, with an absolute visual magnitude of -. If such a star were as near to us as Sirius, it would
have an apparent magnitude of about –10 and give us about a fifth the light of a full moon!
The surface temperature of Betelgeuse is that of a typical M-type red supergiant, about 3100 K. Only about 13% of
the radiant energy is emitted in the form of visible light, and Betelgeuse would therefore appear as the brightest star
in the sky if our eyes were sensitive to radiation at all wavelengths. In volume, Betelgeuse exceeds the Sun by a
factor of at least 160 million. Yet the mass of the star is probably no more than about 20 solar masses, which means
that the average density must be in the range of 2 x10-8 to 9 x 10-8 the density of our Sun. Such star material has a
density of less than one ten-thousandth the density of ordinary air. A star of such tenuous nature has often been
called a “red-hot vacuum”.
M 42
Diffuse Nebula M42 (NGC 1976), an emission and reflection nebula, in Orion
Right Ascension
05 : 35.4 (h:m)
Declination
-05 : 27 (deg:m)
Distance
1.6 (kly)
Visual Brightness
4.0 (mag)
Apparent Dimension
85x60 (arc min)
http://www.seds.org/messier/Jpg/m42.jpg
Discovered 1610 by Nicholas-Claude Fabri de Peiresc.
Located at a distance of about 1,600 (or perhaps 1,500) light years, the Orion Nebula is the brightest diffuse nebula
in the sky, visible to the naked eye, and rewarding in telescopes of every size, from the smallest glasses to the
greatest Earth-bound observatories and the Hubble Space Telescope.
It is the main part of a much larger cloud of gas and dust which extends over 10 degrees well over half the
constellation Orion. The linear extend of this giant cloud is well several hundreds of light years. It can be visualized
by long exposure photos (see e.g. Burnham) and contains, besides the Orion nebula near its center, the following
objects, often famous on their own: Barnard's Loop, the Horsehead Nebula region, and the reflection nebulae around
M78.
The gaseous nature of the Orion Nebula was revealed in 1865 with the help of spectroscopy by William Huggins. In
September 1880, M42 was the first nebula to be successfully photographed, by Henry Draper.
M42 itself is apparently a very turbulent cloud of gas and dust, full of interesting details, which C.R. O'Dell
compares to the rich topography of the Grand Canyon in his HST photo caption. At In the bright center of M42
there's a cluster of newly formed stars, called the "Trapezium cluster". The Trapezium cluster is among the very
youngest clusters known, with new stars still forming in this region.
An excellent review of the astrophysics of the Orion Nebula is provided in 2003 with the superb monograph by
Charles Robert O'Dell (O'Dell 2003), who summarizes the knowledge of that time, including HST research.
It is very easy to find the Orion Nebula, as it surrounds the Theta Orionis multiple star or cluster, seen to the naked
eye in the middle of the sword of Orion. Already under fairly good conditions, the nebula itself can be glimpsed
with the naked eye as a faint nebulosity around this star.