CAPELLA (ALPHA (α) AURIGAE)
RED (YELLOW) GIANT STAR

Right Ascension:
5h 16m 41s

Best Seen:
12/1 - 5/15

Declination:
45º 59' 53"

Magnitude:
0.08

Computer File:
capella

Constellation:
Auriga

Actual

Compared to Sun

Distance

42 l.y.

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Actual Brightness

--

122

Surface Temperature

9,400 ºF

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)

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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.

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

  2. 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.

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

  4. 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.

  5. 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.

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

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

  3. 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.

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

  5. C and D take about 390 years to orbit each other.

Item
Updated Notes

Coordinates 01-07-2003
tweaked a bit, OK with Scott’s The Flamsteed Collection and SIMBAD

Magnitude
01-07-2003
OK with Flamsteed and SIMBAD

Distance
01-07-2003
previously 45 – BUT Flamsteed says 42.2

Actual Brightness
01-07-2003
previously 90 – BUT Flamsteed says 122

Surface Temperature 01-07-2003
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
01-07-2003
close enough to http://www.astro.uiuc.edu/~kaler/sow/capella.html

Mass
01-07-2003
close enough to http://www.astro.uiuc.edu/~kaler/sow/capella.html

Surface Gravity

Surface Composition 01-07-2003
OK for al stars

Spectral Type
01-07-2003
previously G8III – BUT this ok with Flamsteed and SIMBAD

Density

Other Information
01-07-2003
info from http://www.solstation.com/stars2/capella4.htm Previously had companion info, which is updated (and rounded off) with above site