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Sigma (σ) Orionis
Multiple Star System
Right Ascension | 5h 38m 45s | Best Seen | 1/1 - 3/15 |
Declination | -2° 36' 00" | Combined Magnitude | 3.73 |
Apparent Separation | 41.0" | Constellation | Orion |
Actual |
Compared to Sun |
|
Distance | 1,150 ly | -- |
Separation | ~ 1.5 trillion miles | 17,000 au |
Orbital Period | varies - see below | -- |
Actual Brightness | varies - see below | -- |
Magnitude | varies - see below | -- |
Mass | -- | -- |
Surface Gravity | -- | -- |
Surface Composition (by mass) | 74% hydrogen 24% helium 2% everything else |
same |
Spectral Type | 09 V / B2 V / B2 V | G2 V |
Density (gram/cubic cm) | -- | -- |
What To Look For Through The Telescope
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Recommended eyepiece: 24mm or 40 mm.
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When people look through the telescope they should see at least three stars near each other.
Sigma Orionis Information:
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This system actually consists of five stars, three – maybe four – of which can be seen with the telescope.
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The "major" stars are Stars AB and Star E. They are about 1.5 trillion miles away from each other.
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The brighter star is actually two stars, "A" and "B"
Apparent Separation ~ 0.25"
between A and BActual Distance ~ 90 au
between A and B
only takes about 170 years to orbit each otherc. Star A
Actual brightness about 2400 times that of the Sun Magnitude 4.1 Spectral Type O9.5 d. Star B
Actual brightness about 778 times that of the Sun Magnitude 5.2 Spectral Type B0.5 e. Star C (star closest to Star AB)
Apparent Separation ~ 11.0"
between AB and CActual Distance ~ 3,900 au
between AB and CMagnitude ~ 9 Spectral Type A -
Further away from AB, but brighter than C, are two other stars, Stars D and E.
a. Star D
Apparent Separation ~ 12.0"
between AB and DActual Distance ~ 4,600 au
between AB and DActual Brightness ~ 171 x Sun Magnitude ~ 7 Spectral Type B2 b. Star E
Apparent Separation ~ 41.0"
between AB and EActual Distance ~ 15,000 au
between AB and EActual Brightness ~ 212 x Sun Magnitude ~ 7 Spectral Type B2
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References
Item | Updated | Notes |
Coordinates | 2002-10-14 | tweaked a bit |
Combined Magnitude | 2002-10-18 | OK with Scott’s The Flamsteed Collection |
Apparent Separation | 2002-11-08 | based on coordinates given in Flamsteed |
Distance | 2002-10-18 | previous: 1400 ly – BUT updated with Scott’s Flamsteed |
Separation | 2002-11-08 | previous: actual: 1600 trillion miles – BUT "compared to sun" gives approx right answer |
Orbital Period | -- | |
Actual Brightness | 2002-11-08 | previous: 5,000 (Sun) |
Magnitude | 2002-11-08 | too many to put in table |
Mass | -- | |
Surface Gravity | -- | |
Surface Composition | 2003-01-06 | OK for all stars |
Spectral Type | 2002-11-08 | based on Star AB and Star E |
Density | -- | |
Other Information | 2002-11-08 | info from Flamsteed, Scott’s Starlist 2000, and http://www.astro.uiuc.edu/~kaler/sow/sigmaori.html |