Castor, alpha Geminorum (Visual triple star)
Constellation
RA / DEC
Magnitude A / B / C
Separation A-BC/ AC
Position angle A-BC / AC
Spectral class A / B / C
Colour A / B / C
RA / DEC
Magnitude A / B / C
Separation A-BC/ AC
Position angle A-BC / AC
Spectral class A / B / C
Colour A / B / C
: Gemini
: 07:35:14 / +31 52
: 1.9 / 2.9 / 9.1
: 4.4" / 71"
: 61° / 164°
: A1V / A1V / M1Ve
: White / White / Yellow-orange
: 07:35:14 / +31 52
: 1.9 / 2.9 / 9.1
: 4.4" / 71"
: 61° / 164°
: A1V / A1V / M1Ve
: White / White / Yellow-orange
Detail sketch:
Date / Time
Observing Location
Seeing / Transparency
Telescope
Eye-piece
Magnification / Field of View '
Observing Location
Seeing / Transparency
Telescope
Eye-piece
Magnification / Field of View '
: 16/02/10 / 22:24
: Landgraaf
: 5 / 3
: Orion Optics UK 300mm
: 7mm Pentax XW
: 229x / 18
: Landgraaf
: 5 / 3
: Orion Optics UK 300mm
: 7mm Pentax XW
: 229x / 18

Observing Report
With the 22mm Nagler and a magnification of 72x Castor shows a hint of being a double. In The 17mm Nagler, magnification 94x, alpha Geminorum is easily split. The best views however of the two brightest members of Castor are achieved with the 7mm Pentax XW and a magnification of 229x. The view of the two bright white components is simply stunning. Two sparkling white diamonds of almost equal brightness. The southernmost of the two seems a little brighter than the northern component.
Two bright sets of diffraction spikes add to the beauty of this bright double. Amazing how beautiful bright stars look in my 12-inch telescope. This again proves that you should not only use a large telescope for hunting faint fuzzies from exotic catalogues. You should definitely use your large telescope to (re-)visit well-known bright objects like bright stars and bright, well-known deepsky objects, like the ones from the Messier- or Caldwell catalogue.
To the southeast of the bright Castor A and B components, lies a trio of fainter stars, from which the middle star looks deep yellow or even orange. This is the C-component of Castor, the variable YY Geminorum. To the northwest I detect another faint star. The six stars in the field of view remember me of a big airplane or jet, maybe even a Concord, with the two bright stars at the centre.
Two bright sets of diffraction spikes add to the beauty of this bright double. Amazing how beautiful bright stars look in my 12-inch telescope. This again proves that you should not only use a large telescope for hunting faint fuzzies from exotic catalogues. You should definitely use your large telescope to (re-)visit well-known bright objects like bright stars and bright, well-known deepsky objects, like the ones from the Messier- or Caldwell catalogue.
To the southeast of the bright Castor A and B components, lies a trio of fainter stars, from which the middle star looks deep yellow or even orange. This is the C-component of Castor, the variable YY Geminorum. To the northwest I detect another faint star. The six stars in the field of view remember me of a big airplane or jet, maybe even a Concord, with the two bright stars at the centre.
Notes
Each of the three components of Castor are spectroscopic binaries itself, so in fact Castor is a sextuple star system. Component C, with the variable designation YY Geminorum is an eclipsing binary, consisting of two cool M-type stars.