ALPHA (α) CAPRICORNI
OPTICAL DOUBLE STAR

Right Ascension:
20h 17m 51s

Best Seen:
9/1 - 11/15

Declination:
-12º 31' 06"
Combined
Magnitude:
4.30

Computer File:
alphacap

Constellation:
Capricorn

Apparent
Separation: 389"

Actual

Compared to Sun

Distance

686 / 109 l.y.

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Actual Brightness

--

584 / 32

Magnitude

4.44 / 3.58

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Mass

--

5 / 2.5

Surface Gravity

--

--

Surface Composition (by mass)

74% hydrogen 24% helium 2% everything else

same

Spectral Type

G3Ib / G8III (?)

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 they should see two stars next to each other. One star should be slightly brighter than the other.

ALPHA CAPRICORNI INFORMATION:

  1. This star is also called Algedi, from the Arabic meaning “the kid” (a young goat) and it refers to the whole constellation of Capricorn.

  2. Since both stars can be seen with the unaided eye, it is unclear whether “Algedi” refers to both stars, or just the brightest star.

  3. Note that despite their similar magnitude, one is much farther – and much more luminous – than the other.

  4. Though most stars with the name “alpha” are the brightest star in their constellation, with the combined magnitude of the two stars, Alpha Capricorni is actually the third brightest star in Capricorn (delta capricorni is the brightest). It could be named “alpha” because of its position in the constellation, resulting in it being the first star named.

  5. *INCLUDE THIS?** Through a telescope, both components of Alpha Capricorni have faint companions. Plus, SIMBAD says both stars are a “star in double system.” It is unclear whether the components and their companions form optical doubles or multiple stars.

Item
Updated Notes

Coordinates 11-26-2002
split difference between two

Combined Magnitude
11-26-2002
with Scott’s The Flamsteed Collection

Apparent Separation 11-26-2002
from coordinates

Distance
11-26-2002
from Flamsteed and SIMBAD

Actual Brightness
11-26-2002
from Flamsteed

Magnitude
11-26-2002
from Flamsteed

Mass
11-26-2002
http://www.astro.uiuc.edu/~kaler/sow/algedi.html

Surface Gravity

Surface Composition 01-06-2003
OK for all stars

Spectral Type
11-26-2002
alf01 cap SIMBAD says G3Ib Flamsteed says G3Ib alf02cap SIMBAD says G6/G8III Flamsteed says G9III

Density

Other Information
11-26-2002
http://www.astro.uiuc.edu/~kaler/sow/algedi.html