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Castor Aa
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Star Castor Aa

Multiple star system Castor Aa is located 51 light years away from the Sun. It is a system with 6 stars. For now, there are no known exoplanets in this star system.
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Sun distance
51 light years
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Castor Aa

White-Blue star
Spectral class: A1V

Location +

Ascension iconRight ascension: 7h 34m 35.879s
Declination iconDeclination: 31° 53' 17.816'' (northern hemisphere)
Parallax iconParallax: 64.120
Distance iconSun distance: 50.867 ly | 15.6 pc
Star position
The position of a star tells us where it appears in the sky, similar to how we use coordinates like latitude and longitude on Earth. In astronomy, the three main coordinates are right ascension, declination and distance. .. icon More about Star position in StellarGuide

Basic characteristic

icon weight
Mass: 276 % M Sun
| 2891 M Jupiter
+
Star mass
Mass of the star Castor Aa is 2.76 solar masses.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 240 % R Sun
| 23.9 R Jupiter
+
Star size
Radius of the star Castor Aa is 2.4 solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature icon
Temperature: 10286 K | 1.78 T Sun
+
Star temperature
Surface temperature of Castor Aa is 10286 K, which is 178 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide

Photometry

Magnitude iconApparent magnitude (V): 1.6
Magnitude iconAbsolute magnitude (V): 0.6
Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3

Castor Ab

Red dwarf
Spectral class: dM1e

Basic characteristic

icon weight
Mass: 50 % M Sun
| 534.3 M Jupiter
 (estimate)
+
Star mass
The mass of the star Castor Ab is unknown. Based on its other characteristics, it is estimated to be about 50 % of the Sun's mass.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 50 % R Sun
| 5.3 R Jupiter
(estimate)
+
Star size
Radius of the star Castor Ab is not known. Its estimated value based on other similar stars is about 50 % solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature iconTemperature: 3700 K
 (estimate)
+
Star temperature
Surface temperature of Castor Ab is estimated to be 3702 K, which is 64 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide

Photometry

Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3

Castor Ba

White-Blue star
Spectral class: A2Vm

Basic characteristic

icon weight
Mass: 298 % M Sun
| 3122 M Jupiter
+
Star mass
Mass of the star Castor Ba is 0.51 solar masses.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 330 % R Sun
| 32.8 R Jupiter
+
Star size
Radius of the star Castor Ba is 3.3 solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature icon
Temperature: 8842 K | 1.53 T Sun
+
Star temperature
Surface temperature of Castor Ba is 8842 K, which is 153 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide

Photometry

Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3

Castor Bb

Red dwarf
Spectral class: dM1e

Basic characteristic

icon weight
Mass: 50 % M Sun
| 534.3 M Jupiter
 (estimate)
+
Star mass
The mass of the star Castor Bb is unknown. Based on its other characteristics, it is estimated to be about 50 % of the Sun's mass.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 50 % R Sun
| 5.3 R Jupiter
(estimate)
+
Star size
Radius of the star Castor Bb is not known. Its estimated value based on other similar stars is about 50 % solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature iconTemperature: 3700 K
 (estimate)
+
Star temperature
Surface temperature of Castor Bb is estimated to be 3702 K, which is 64 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide

Photometry

Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3

Castor Ca

Red dwarf, BY Draconis variable
Spectral class: M0.5VeFe-2

Basic characteristic

icon weight
Mass: 59.9 % M Sun
| 628 M Jupiter
+
Star mass
Mass of the star Castor Ca is 0.51 solar masses.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 62 % R Sun
| 6.2 R Jupiter
+
Star size
Radius of the star Castor Ca is 0.6191 solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature icon
Temperature: 3820 K | 0.66 T Sun
+
Star temperature
Surface temperature of Castor Ca is 3820 K, which is 66 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide
time icon
Age: 0.370 billions years | 0.08 Sun
+
Star age
Star Castor Ca is 0.370 billion years old, which is about 0.08 of the Sun's age.

The age of a star tells us how long it has been shining since it formed. Knowing a star’s age helps astronomers understand its life stage, how it has changed over time, and what will happen to it in the future... icon More about Star age in StellarGuide
luminosity icon
Luminosity: 0.0733 L Sun
+
Star luminosity
Luminosity is the total amount of energy a star gives off every second. Think of it as the star’s true brightness — not just how bright it looks from Earth. This is important because some stars may appear dim simply because they are far away, not because they’re actually faint... icon More about Star luminosity in StellarGuide

Photometry

Magnitude iconApparent magnitude (V): 9.3
Magnitude iconAbsolute magnitude (V): 8.4
Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3

Castor Cb

Red dwarf, , BY Draconis variable
Spectral class: dM1e

Basic characteristic

icon weight
Mass: 59.9 % M Sun
| 628 M Jupiter
+
Star mass
Mass of the star Castor Cb is 0.5992 solar masses.

The mass of a star is the total amount of matter it contains. It is one of the most important properties of a star, as it determines almost everything about how the star lives, changes, and dies. In astronomy, star mass is usually measured in solar masses (M☉) — where 1 solar mass is equal to the mass of our Sun... icon More about Star mass in StellarGuide
radius icon
Size: 62 % R Sun
| 6.2 R Jupiter
+
Star size
Radius of the star Castor Cb is 0.6191 solar radii.

The size of a star refers to its radius — the distance from its center to its surface. Star size is usually measured in solar radii (R☉), where 1 solar radius equals approximately 696,000 kilometers. Depending on their type and life stage, stars can be much smaller or larger than the Sun... icon More about Star size in StellarGuide
temperature icon
Temperature: 3820 K | 0.66 T Sun
+
Star temperature
Surface temperature of Castor Cb is 3820 K, which is 66 % of the temperature on the surface of the Sun.

The temperature of a star refers to the temperature at its surface, also called the photosphere. It is measured in kelvins (K), the standard unit for temperature in astronomy. A star’s temperature tells us a lot about its physical properties and where it stands in its evolutionary stage... icon More about Star temperature in StellarGuide
time icon
Age: 0.37 billions years | 0.08 Sun
+
Star age
Star Castor Cb is 0.37 billion years old, which is about 0.08 of the Sun's age.

The age of a star tells us how long it has been shining since it formed. Knowing a star’s age helps astronomers understand its life stage, how it has changed over time, and what will happen to it in the future... icon More about Star age in StellarGuide
luminosity icon
Luminosity: 0.0733 L Sun
+
Star luminosity
Luminosity is the total amount of energy a star gives off every second. Think of it as the star’s true brightness — not just how bright it looks from Earth. This is important because some stars may appear dim simply because they are far away, not because they’re actually faint... icon More about Star luminosity in StellarGuide

Photometry

Absolute stellar magnitude in different parts of the electromagnetic spectrum from infrared (K band) to ultraviolet (U band).
5
10
15
20
25
30
35
K
2.1
H
1.6
J
1.2
Grp
0.8
I
0.8
G
0.6
V
0.5
Gbp
0.5
B
0.4
U
0.3
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Castor Aa system structure

 Castor Aa
Castor Ab
Castor Ba
Castor Bb
Castor Ca
Castor Cb

More about Castor Aa

      a BY Draconis variable. Stars from this category exhibit periodic variations in their luminosity. The variability is caused by a rotation which shows and hides starspots on the surface. Castor Aa can be found in northern celestial hemisphere, and it is possible to see it with naked eye. The star is easily observable from Northern America, Europe and Asia. 

      Castor Aa is a BY Draconis variable. Stars from this category exhibit periodic variations in their luminosity. The variability is caused by a rotation which shows and hides starspots on the surface.
Other designations of this star
BD+32°1581B, HR 2890, HD 60178, Alpha Geminorum, α Gem, 66 Geminorum, FK5 287, GJ 278, Gliese 278, HIP 36850, SAO 60198, BD+32°1581A, PLX 1785.00, HR 2891, HD 60179, V* YY Gem, YY Geminorum, BD+32°1582
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Frequently Asked Questions

How far is the Castor Aa system from the Sun?

The Castor Aa system is 51 light years or 15.6 parsecs from the Sun.

What galaxy is the Castor Aa star in?

The Castor Aa is in the Milky Way galaxy just like the Sun.

How many stars are in the Castor Aa system?

The Castor Aa system contains 6 stars.

What type of star is the Castor Aa?

The primary in the Castor Aa system is a White-Blue star star.

What temperature is star Castor Aa?

The primary in the Castor Aa system has a temperature of 10286 K. Find out more about the temperature of stars in Stellar guide
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