Moon and Gemini stars on April 8 and 9

Two dots labeled Pollux and Castor with a half-moon shape above and below, plus dot for Procyon on left.
The moon passes the bright stars Castor and Pollux in Gemini the Twins on April 8 and 9. The moon reaches its 1st-quarter phase on April 9. Chart via John Jardine Goss.

Moon and Gemini stars

On April 8 and, 9, 2022, you’ll find the a 1st-quarter moon near Castor and Pollux, the two brightest stars in the constellation Gemini the Twins.

Also nearby is Procyon, the brightest star in the constellation Canis Minor the Lesser Dog. Procyon might be hard to pick out without the help of tonight’s moon, or a good constellation chart. On the other hand, Castor and Pollux are extremely noticeable in the night sky, moon or no moon. No other two such bright stars appear so close together.

A closer look at Castor and Pollux

Regardless of the seeming connection between these two stars, Castor and Pollux aren’t close together in space. They just happen to reside along the same line of sight from Earth.

Both Castor and Pollux are bright stars, and they’ve been known as Twins for centuries. But they don’t really look alike. Pollux is golden in color, and Castor is pure white. If you have binoculars, they’ll help you to more easily distinguish the color contrast between Castor and Pollux.

Also, Castor and Pollux are different kinds of stars. Castor is a hot, white-colored star that is well known for being a multiple star system. It consists of three pairs of binary stars, that is, six stars bound together in an intricate gravitational dance. Pollux is a cool and bloated orange-colored star, said to be the closest giant star to Earth. A star with the mass of our sun swells up into a red giant in its old age. But our sun won’t become a red giant for another 4-5 billion years or so, according to astronomers.

Sun tiny like a BB, Pollux like a baseball, Arcturus like a basketball, each labeled.
You can see the comparative size of the star Pollux and our sun in this image, as well as some other stars. Pollux is a giant star by virtue of its age. Many stars – including our sun – will swell to the giant stage as they age.

Mythology associated with Castor and Pollux

In many cultures, Castor and Pollux were seen as twin stars, usually as heroes. Many old sky myths invoke the idea of twins to explain their proximity on the sky’s dome.

In Greek and Roman mythology, Castor and Pollux were the twin sons of Jupiter and Leda and brothers of Helen of Troy. They sailed with Jason as two of his Argonauts.

Pollux, represented by the brighter star, was immortal, but his brother Castor was not. When Castor was killed in a fight, Jupiter wanted the two to remain together, so he decreed that they each should spend some time in the underworld and some time in the heavens. This is a fanciful way of explaining why the constellation is above the horizon for part of each day and below the horizon for the rest. Castor and Pollux are sometimes said to represent brotherly love.

Meanwhile, in China, these two stars were associated with water, as part of constellations representing rivers. They were sometimes also seen as the complementary elements of yin and yang.

Antique color etching of twin boys with lyre, club and bow in a star field.
Castor and Pollux, the Gemini twins, via Wikipedia.

Other interesting facts about Gemini

Because Gemini is a constellation of the zodiac, the sun passes in front of this constellation for about a month each year, from about June 21 to July 20.

Gemini is also host to the annual Geminid meteor shower every December. The radiant point – the point in our sky from which the meteors seem to radiate – of this strong and popular meteor shower is near Castor.

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Diagram with two bright stars, lines of stars, and radial arrows.
If you have a dark sky, notice that 2 nearly parallel streams of stars extend from Castor and Pollux. These stars likely reinforced the idea of twins in various cultures around the world. Every December, the Geminid meteor shower radiates from near star Castor in Gemini.

Bottom line: The moon is near the stars Castor and Pollux in the constellation Gemini the Twins on April 8 and 9, 2022. These stars represent twins in many cultures.

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April 8, 2022

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