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Alpha (α) Aurigae
Capella
Red (Yellow) Giant Star
Right Ascension | 5h 16m 41s | Best Seen | 12/1 - 5/15 |
Declination | 45° 59' 53" | Magnitude | 0.08 |
Constellation | Auriga | ||
Actual | Compared to Sun | |
Distance | ~42 ly | -- |
Actual Brightness | -- | 122 |
Surface Temperature | ~9,400 °F | ~0.94 |
Diameter | ~ 10 million miles | ~ 11 |
Mass | -- | ~ 3 |
Surface Gravity | -- | -- |
Surface Composition (by mass) | 74% hydrogen 24% helium 2% everything else |
same |
Spectral Type | G5 IIIe | 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 a bright yellowish point of light should be seen.
Capella Information:
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Capella is 4th brightest star in the Northern Hemisphere’s night sky (6th brightest if including the Southern Hemisphere’s bright stars).
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The name “Capella” derives from the Latin for “She-goat”, referring to goats carried by Auriga (the name of the constellation).
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While only one star is seen through the telescope, Capella is actually a multiple star system, with at least 4 components. (They cannot be seen because Capella is far away from us, and the components are quite close to each other.)
a. Stars Capella A and Capella B are a spectroscopic multiple.
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Both A and B are giant stars, a bit past the hydrogen-fusing, main-sequence phase of their lives.
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Capella A is spectral type G8-K0 III, is about 3 times the mass of the sun, about 12 times its diameter, and about 80 times brighter.
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B is spectral type G1 III, slightly less massive, smaller, and not as bright as Capella A.
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A and B are only about 68 million miles away from each other (0.73 AU), about the same distance from our Sun to the planet Venus.
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They only take 104 days to orbit each other. Venus and our sun take 225 days.
b. Stars Capella C and Capella D are about 11,000 AU’s (0.17 light years) from A and B.
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Both C and D are “red dwarfs”, cool stars that are still in the hydrogen-fusing, main-sequence phase of their lives.
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Capella C is spectral type M1V, is only 30-40% the mass of our sun, half its diameter, and about as bright.
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Capella D is spectral type M4-5 V, only a tenth of our sun’s mass, only 23-30% its diameter, and only 0.05% as bright.
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C and D are about 4 1/2 billion miles away from each other (48 AU), further than Pluto is from our Sun.
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C and D take about 390 years to orbit each other.
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References
Item | Updated | Notes |
Coordinates | 2003-01-07 | tweaked a bit, OK with Scott’s The Flamsteed Collection and SIMBAD |
Magnitude | 2003-01-07 | OK with Flamsteed and SIMBAD |
Distance | 2003-01-07 | previously 45 – BUT Flamsteed says 42.2 |
Actual Brightness | 2003-01-07 | previously 90 – BUT Flamsteed says 122 |
Surface Temperature | 2003-01-07 | previously 7,500 ºF – BUT with temp range given in Flamsteed, for G star 4900-6000K, with Capella being G5, temp will fall in middle, at 5450 K |
Diameter | 2003-01-07 | close enough to http://www.astro.uiuc.edu/~kaler/sow/capella.html |
Mass | 2003-01-07 | close enough to http://www.astro.uiuc.edu/~kaler/sow/capella.html |
Surface Gravity | -- | |
Surface Composition | 2003-01-07 | OK for al stars |
Spectral Type | 2003-01-07 | previously G8III – BUT this ok with Flamsteed and SIMBAD |
Density | -- | |
Other Information | 2003-01-07 | info from http://www.solstation.com/stars2/capella4.htm Previously had companion info, which is updated (and rounded off) with above site |