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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


  1. Recommended eyepiece: 24mm or 40 mm.

  2. When people look through the telescope a bright yellowish point of light should be seen.


Capella Information:


  1. Capella is 4th brightest star in the Northern Hemisphere’s night sky (6th brightest if including the Southern Hemisphere’s bright stars).

  2. The name “Capella” derives from the Latin for “She-goat”, referring to goats carried by Auriga (the name of the constellation).

  3. 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.

    • Both A and B are giant stars, a bit past the hydrogen-fusing, main-sequence phase of their lives.

    • 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.

    • B is spectral type G1 III, slightly less massive, smaller, and not as bright as Capella A.

    • 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.

    • 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.

    • Both C and D are “red dwarfs”, cool stars that are still in the hydrogen-fusing, main-sequence phase of their lives.

    • Capella C is spectral type M1V, is only 30-40% the mass of our sun, half its diameter, and about as bright.

    • 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.

    • C and D are about 4 1/2 billion miles away from each other (48 AU), further than Pluto is from our Sun.

    • 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