Gamma Geminorum facts for kids
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| Observation data Epoch J2000 Equinox J2000 |
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| Constellation | Gemini |
| Right ascension | 06h 37m 42.71050s |
| Declination | +16° 23′ 57.4095″ |
| Apparent magnitude (V) | 1.915 |
| Characteristics | |
| Evolutionary stage | subgiant |
| Spectral type | A1IV + G |
| U−B color index | +0.137 |
| B−V color index | +0.005 |
| Astrometry | |
| Radial velocity (Rv) | −12.5 km/s |
| Proper motion (μ) | RA: +13.81 mas/yr Dec.: −54.96 mas/yr |
| Parallax (π) | 29.84 ± 2.23 mas |
| Distance | 109 ± 8 ly (34 ± 3 pc) |
| Absolute magnitude (MV) | −0.68 |
| Orbit | |
| Period (P) | 4,614.51 days |
| Eccentricity (e) | 0.8933±0.0013 |
| Periastron epoch (T) | 244399.13±0.77 |
| Argument of periastron (ω) (secondary) |
312.60±0.60° |
| Semi-amplitude (K1) (primary) |
11.881±0.068 km/s |
| Details | |
| γ Gem A | |
| Mass | 2.81 M☉ |
| Radius | 6.06+0.43 −0.49 R☉ |
| Luminosity | 207.3+37.2 −31.5 L☉ |
| Surface gravity (log g) | 3.56±0.08 cgs |
| Temperature | 9,190±130 K |
| Metallicity [Fe/H] | −0.12 dex |
| Rotational velocity (v sin i) | 10.7±0.2 km/s |
| γ Gem B | |
| Mass | 1.07 M☉ |
| Other designations | |
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Alhena, 24 Geminorum, BD+16°1223, FK5 251, GCTP1539.00, HIP 31681, HD 47105, HR 2421, SAO 95912
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| Database references | |
| SIMBAD | data |
Alhena (also known as Gamma Geminorum or γ Geminorum) is a bright star in the constellation of Gemini. It is the third brightest object you can see in Gemini. Alhena shines with an apparent magnitude of 1.9, which means it is easy to spot with your naked eye, even from cities. This star is about 109 light-years away from Earth. Scientists measured this distance using a method called parallax, which involves observing how the star's position seems to shift as Earth orbits the Sun.
Contents
Exploring Alhena: A Star in the Gemini Constellation
Alhena is a fascinating star that is currently changing. It is using up the hydrogen fuel in its core. This process means it has moved into a stage called a subgiant. A subgiant star is bigger and brighter than it was when it was younger.
What Makes Alhena Special?
Alhena is much larger and brighter than our Sun. It has about 2.8 times the mass of the Sun. Its size is roughly six times the Sun's radius. Alhena shines with about 200 times the light of our Sun. Its surface temperature is very hot, around 9,190 Kelvin. This high temperature gives Alhena a beautiful white color, typical for stars of its type.
Alhena's Hidden Companion
Did you know Alhena is not alone? It is part of a binary system. This means it has a companion star orbiting it. We call this a spectroscopic binary because astronomers detect the companion by studying Alhena's light. The two stars complete an orbit around each other every 12.6 years. Their path is quite stretched out, which astronomers call an eccentric orbit. The companion star is thought to be similar to our Sun, a G-type main-sequence star.
The Story Behind Alhena's Name
The name Alhena has a long history, coming from ancient cultures. Understanding star names helps us learn about how people viewed the sky long ago.
Alhena's Arabic Roots
The name Alhena comes from the Arabic phrase Al Han'ah. This means 'the brand' or 'mark' on a camel's neck. Another old name for this star was Almeisan, which means 'the shining one' in Arabic. In 2016, the International Astronomical Union (IAU) officially approved the name Alhena for this star. The IAU is a group that helps name and categorize celestial objects.
Alhena in Chinese Astronomy
In Chinese astronomy, Alhena is part of an asterism called Jǐng Su. This translates to the "Well" asterism. Alhena is known as Jǐng Su sān, which means 'the Third Star of Well'. This shows how different cultures have organized and named the stars in their own unique ways.
Alhena's Place in the Night Sky
Alhena is located close to the ecliptic. The ecliptic is the imaginary path the Sun appears to follow across the sky. It is also where the Moon and planets usually travel.
Celestial Alignments with Alhena
Because Alhena is a little south of the ecliptic, the Moon never passes directly in front of it. This event is called an occultation. Planets also usually pass a few degrees north of Alhena. However, the planet Venus will have several very close encounters with Alhena. These close approaches will begin in August 2143 and happen every eight years after that for the rest of that century. Each year, around June 30, the Sun appears to pass by Alhena in the sky.
Alhena's Legacy in Culture
Stars often inspire names for things on Earth, and Alhena is no exception.
Ships Bearing the Name Alhena
The name Alhena has been given to ships. For example, a Dutch ship named Alhena helped rescue many people. This happened in October 1927, when an Italian cruise liner, the SS Principessa Mafalda, faced trouble. Later, an American attack cargo ship was also named USS Alhena (AKA-9) after this bright star.
