One of 48 ancient and 88 modern constellations, Gemini was first described by the astronomer Ptolemy in the 2nd century.
The following article summarizes the facts and mythology surrounding one of the most fascinating constellations in the heavens.
Gemini Constellation Facts, Myth, Location and Stars
How To Locate the Gemini Constellation
The Constellation Gemini lies in the second quadrant of the northern hemisphere.
Orion, Cancer, and Taurus are its famous neighbors.
Visible in the northern hemisphere from November through April, Gemini reaches its highest point at 10 p.m. (regardless of time zone).
In the southern hemisphere, we can see the constellation from December through March.
How Gemini Constellation Got Its Name
Gemini is Latin for twins and is associated with Castor and Pollux, who were twins in Greek mythology.
If we were to trace lines between the most prominent stars in the constellation, we could imagine two stick figures lying sideways and holding hands.
The two brightest stars represent the heads of Castor and Pollux.
Gemini Constellation in Other Cultures
According to Greek mythology, Castor and Pollux are the twins in Gemini.
In Babylonian astronomy, the stars Pollux and Castor were called the Great Twins.
In Egyptian astrology, the constellation was associated with twin goats, and in Arabian astrology, twin peacocks.
Another twin pair associated with Gemini are the mythical founders of Rome, Romulus and Remus.
And in Chinese philosophy, Castor and Pollux represent Yin and Yang.
Gemini Constellation Mythology: Myth of Castor and Pollux
In Greek mythology, Castor and Pollux were the children of Leda, the wife and queen of King Tyndarus of Sparta.
Castor, a legendary horseman, was the mortal son of Tyndarus, while Pollux, a renowned warrior, was the immortal son of Zeus and Leda.
Conceived by different fathers, they shared the same womb.
According to the myth, Castor was also skilled at fencing and taught Heracles/Hercules this art.
Although half-brothers, Castor and Pollux were devoted to each other.
And when Castor was killed in a battle, the immortal Pollux implored Zeus to make Castor immortal, as well.
Zeus agreed and turned them both into the bright stars that bear their names.
Gemini as a Constellation of the Zodiac
In astrology, Gemini is the third of 12 zodiac signs, governing the period from about May 21 to June 21.
In Western culture, the zodiac signs are twelve, 30-degree sectors that represent a complete orbit of the Earth around the Sun.
Each sign was named after a constellation through which the sun moved, annually.
Over the centuries, the Western zodiac divisions have shifted out of alignment with the constellations due to Earth’s axial precession (a change in its rotational axis).
The Major Stars of the Gemini Constellation
The Gemini constellation includes 85 stars that can be seen with the naked eye.
As an interesting sidebar, astronomers have identified eight stars that host planets.
Ten of the stars have official names and the following is a list of several major stars.
- Alhena, designated as Gamma Geminorum, is the third brightest star in Gemini. About 109 light-years away from us, it’s 123 times brighter than the Sun, 160% hotter, 281% denser, and 330% larger. The name, Alhena, means brand in Arabic, referring to the brand on a camel’s neck.
- Castor or Alpha Geminorum is the second brightest, blue-white star, and is 52 light-years from Earth. It’s an example of a sextuple star system (three pairs of binary stars held together by gravitational forces).
- Mebsuta or Epsilon Geminorum is a yellow supergiant about 840 light-years away. It is enormous, having around 1,920% of the Sun’s mass, and 14,000% of its radius. Additionally, it’s 8500 times brighter than our Sun. The proper name means outstretched paw in Arabic.
- Pollux or Beta Geminorum is the brightest star in the constellation and the 17th brightest star in the night sky. An orange giant, it’s 33.78 light-years away. In 2006, a planet was confirmed to be orbiting the star. The planet, known as Pollux b, has a mass of 2.3 times that of Jupiter and an orbit of 590 days. Pollux has twice the Sun’s mass and about nine times its radius.
- Propus or Eta Geminorum is a triple star system (three stars bound by gravity) in Gemini and is about 380 light-years from the Sun. Propus means forefoot in Latin, which is a clue about where it can be found in Gemini. It’s classified as a variable star, which means that its brightness varies, as seen from Earth.
- Tejat (backfoot in Arabic) or Eta Geminorum is approximately 350 light-years from Earth. It has 210% of the Sun’s mass, 8,000% of its radius, and it is 1,148 times brighter. It’s a multiple star consisting of three components: a binary star (two-star system) and a dwarf star that orbits the pair every 700 years.
Celestial Objects Associated with the Gemini Constellation
The Geminids are a meteor shower that seems to radiate from a point in the Gemini Constellation.
This point or object is known as 3200 Phaeton which may be an extinct comet or an asteroid.
The Geminids are uniquely dense meteors, a property that allows them to get close to the Earth’s surface (as close as 29 miles above the surface) before burning up.
This intense meteor shower occurs every year around mid-December.
Other interesting objects in Gemini are the Eskimo Nebula, the Medusa Nebula, the Jellyfish Nebula, and the neutron star Geminga (the collapsed core of a massive supergiant star that exploded in a supernova about 300,000 years ago).
These objects are known as deep-sky objects, meaning that they are not individual bodies such as a planet, moon, or comet.
Practical Applications for Constellations
Before the calendars were created, constellations like Gemini were used to determine the seasons.
For instance, the Gemini Constellation is visible from November through April.
And before navigational instruments were invented, such as the astrolabe and the compass, they guided sailors and explorers.
Today, astronomers use constellations as points of reference to locate (for example) celestial objects.
In our opinion, the Gemini Constellation is among the most interesting of all the constellations.
Not surprisingly, it inspired a space program and an observatory of the same name.
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