The AsterNym star registry
Castor
Castor: the white star of Gemini
white · Gemini · α Gem
Castor is a white star, burning hotter than our own Sun in the constellation Gemini, one of the stars with a proper name recognised in the IAU Catalog of Star Names. At magnitude 1.58 it is visible to the naked eye under a dark sky.
Most stars in the sky are anonymous points of light. Castor is not. Some IAU-recognised names are ancient; others were adopted by the IAU only recently. Either way, the star already has a scientific identity, and a dedication attaches a human story to it.
Real star · Personal dedication · Recorded in the AsterNym registry
See what a dedicated page looks like: preview
Castor at a glance
- Constellation
- Gemini
- Other name
- α Gem
- Catalogue number
- HIP 36850
- Distance
- ≈ 51 light-years
- Brightness
- Magnitude 1.58 naked-eye
- Star type
- A1 V
- Colour
- white
- Best seen from
- The Northern Hemisphere and lower southern latitudes
- Right ascension
- 07h 34m 36s
- Declination
- +31° 53′ 18″
J2000 catalogue coordinates that can be independently cross-checked against astronomical databases. A planetarium app showing coordinates of date will differ slightly, because proper motion and precession move a star’s apparent position over time.
What kind of star is Castor?
Castor is a white main-sequence star. Its surface runs around 7,500 to 10,000°C, hot enough to look white or blue-white to the eye. Colour in a star is a temperature reading rather than a decoration: the hot ones are blue and the cool ones red, the opposite way round to a kitchen tap.
These are the classic bright white stars. Sirius and Vega are both this kind, and they are the reason people describe stars as white when most of the galaxy's stars are actually red and too faint to see.
A star of this class gets roughly a thousand million years, a tenth of what the Sun gets.
It is a main-sequence star, which despite the word dwarf simply means it is in the long stable middle of its life, fusing hydrogen in its core exactly as the Sun is doing now.
The light you are looking at is old
The light you can see from Castor left in 1975, which puts it roughly a lifetime ago. Nobody has invented anything since then that the light knows about; it has simply been travelling.
That delay is the part people find hardest and like most. A star is the one thing you can give someone that was already old before either of you was born and will outlast anything else you could have chosen.
It is also one of the brighter stars in the sky, which is why it carries a proper name at all rather than a catalogue number.
What could a Castor dedication represent?
Castor is especially meaningful for someone who:
- · Deserves something older than any gift shop
- · Marks a beginning, an anniversary or a promise
- · Is remembered every time you look up
- · Has a light you want recorded somewhere permanent
Dedication idea
“For the one I think of when I find Gemini in the sky.”
Where can you see Castor?
It is easy to see from most of the Northern Hemisphere. It can also appear from lower southern latitudes, but it never rises for observers south of about latitude 58°S. It passes directly overhead at latitude 32°N. It stands highest at midnight in January, so January and February evenings are the best time to look. At magnitude 1.58 it is an easy naked-eye star from any reasonably dark spot.
Castor belongs to Gemini.
What does Castor mean in astrology?
The mortal twin, the horseman. Nature of Mercury: wit, versatility, sudden fame through skill of hand or word, and sharper swings of fortune than Pollux.
Projected onto the zodiac the way fixed-star astrology reads any star, Castor stands at 20° Cancer at the J2000 epoch, and the Sun passes that degree around 10 July in the years around 2000. Fixed-star longitude shifts slowly against the tropical zodiac because of precession, about one degree every seventy-two years, so a natal conjunction must be calculated for the birth year rather than read off this J2000 value or a calendar date.
Traditional interpretations, not facts or predictions. The position and dates are computed.
Dedicate Castor to someone who matters
A flower fades. A card is eventually put away. A star gives your message a place in the sky.
from$29.95a year
Dedicate Castor →Real star · your message · a page to share
Your Castor dedication includes
- Your chosen dedication name
- Your personal message
- Castor's real astronomical coordinates
- A shareable dedication page
- Its location on the AsterNym Galaxy Map
- An optional printable certificate and gift presentation
Castor keeps its established astronomical name. Your dedication is a personal commemorative record within the AsterNym registry.
Frequently asked questions about Castor
- What does Castor mean in astrology?
- The mortal twin, the horseman. Nature of Mercury: wit, versatility, sudden fame through skill of hand or word, and sharper swings of fortune than Pollux. Projected onto the zodiac, Castor stands at 20° Cancer, and the Sun passes that degree each year around 10 July.
- Is Castor the brightest star?
- Castor shines at magnitude 1.58 · visible to the naked eye on a clear night, one of the few thousand stars with an officially recognised name.
- How far away is Castor?
- Castor is approximately 51 light-years from Earth. The light reaching us tonight began its journey around 51 years ago.
- Which constellation contains Castor?
- Castor is part of Gemini.
- Can everyone see Castor?
- It is easy to see from most of the Northern Hemisphere. It can also appear from lower southern latitudes, but it never rises for observers south of about latitude 58°S. It passes directly overhead at latitude 32°N. It stands highest at midnight in January, so January and February evenings are the best time to look. At magnitude 1.58 it is an easy naked-eye star from any reasonably dark spot.
- Is dedicating Castor an official astronomical renaming?
- No. Castor keeps its internationally recognised astronomical name. An AsterNym dedication records your personal name and message in the AsterNym registry without changing the star's scientific identity.
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