The Orion Cloud and Association

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The Orion Cloud and Association

[ori_kc.jpg]

In the direction of the constellation Orion, approximately centered on the

Great Orion Nebula M42 and

M43, there

drifts a giant cloud of interstellar gas and dust within the Milky Way galaxy.

This cloud was formed when a density wave, related to the Galaxy’s spiral

structure, moved through the medium of the Galactic disk. It is about 1600

light years away and several hundred light years across.

This giant cloud, or complex of clouds, of interstellar matter and young stars

contains, besides M42 and M43 and the nebulosity associated with them

(NGC 1973-5-7), a number of famous objects:

Barnard’s Loop,

the Horsehead Nebula region

(also containing NGC 2024 = Orion B),

and the reflection nebulae around M78.

Our image on the right shows the whole constellation Orion with bright reddish

Betelgeuse slightly left and above the middle, and bright blueish-white Rigel

at the lower right. The brightest nebula, in the “sword” of Orion and below

his belt stars, is the Great Nebula M42 with M43, with the faint extension to

North (up), NGC 1973-5-7. At the left-most belt star, Zeta Orionis, the

Horsehead Nebula region with Orion B is conspicuous. The huge, delicate bow

around this region, spanning the southern (lower) half of the constellation,

is Barnard’s Loop. Very north in Orion, around the star Lambda, is another

very faint and round, huge nebulous cloud.

Our image was obtained by Sven Kohle and Till Credner of

Bonn, Germany

on October 29, 1995 at 3:25 UT from Calar Alto with a f=55 mm 1/3.5 photo lens

on Kodak Ektachrome 400 Elite film, exposed 60 minutes (without filter).

The image is copyrighted by the observers.


[ori_uks.gif]

UKS image of a great portion of the Orion cloud.

The bright nebula near the bottom is the Great Orion nebula

M42 with its northern part

M43 and northern extension NGC 1973-5-7.

At the upper left is the

nebula complex around the star Zeta Orionis,

consisting of bright Orion B (NGC 2024) left of the star, and IC 434

with the conspicuous dark Horsehead Nebula,

plus various small nebulae.

The whole region is filled with gas and dust, but only parts have yet formed

stars (i.e., clusters) and are thus illuminated.

Barnard’s Loop extends far beyond this

image and cannot be traced here very well, as it is brightest at its edges.

This image is copyrighted and may be used for private purpose

only. For any other kind of use, including internet mirroring and storing on

CD-ROM, please contact

Coral Cooksley of the

Anglo Australian Observatory.


At least three remarkable stars are observed to escape from the Orion complex

with high space velocities:

  • AE Aurigae, a variable of spectral type O9.5 and about 6th magnitude

    (corresponding to an absolute magnitude of – 2.5 at its 1,600 light year

    distance, variations being erratic between 5.4 and 6.1 magnitude, according

    to Burnham), which illuminates the diffuse nebula IC 405, also called the

    “Flaming Star Nebula”, escaping at about 130 km/s,

  • 53 Arietis (apparent mag 6.09, spectrum B2 V) escaping with 60 km/s,
  • Mu Columbae (5.16 mag, spectrum O9.5 V) running away at about 120 km/s.

They must have left the Orion cloud about 2–5 million years ago, and it is

speculated that they might have speeded up somehow during supernova explosions

(perhaps of companion stars in multiple systems).

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