Gemini
Article for April/May 2024
The period of this star sign may not start until the end of the month, but May is the last chance to spot the constellation of Gemini before it dips below the horizon. By June, it will be too low in the sky to see fully by the time it gets dark, and it will not be visible again until it starts to rise once more in the early hours of September mornings. Gemini is currently low in the western sky, visible above the remnants of Orion, who will have already sunk mostly out of sight by sunset.
Drawing a line up from Orion’s red supergiant, Betelgeuse, will take you to a pair of bright stars, Castor and Pollux, named for the twin half-brothers from Greek and Roman mythology, and the constellation’s name-sake (Gemini is Latin for ‘twins’). The brothers, however, are not as alike as they first appear. Pollux, the brighter of the two and 17th brightest star in the night sky, is a yellow-orange hypergiant star, with almost twice the mass of our own sun and nine times as large. Its dimmer brother, Castor, is actually not a single star at all. What looks to us like one star is actually six stars that are gravitationally bound together.
The constellation of Gemini, showing its two brightest stars, Pollux and Castor (image taken from ‘Stellarium’)
Through a telescope you may be able to see Castor separate into two stars, with a fainter third nearby. These are the binary star systems known as Castor A, Castor B, and Castor C. The pairs of stars in these binary star systems are too close together to be visible separately through a telescope. In fact, we can only separate them through using a Spectroscope — a machine that splits the light they give off into its component parts. As each star moves closer or further away, the spectroscope will detect changes in the wavelength of light, which allows astronomers to detect the star.
When we welcome back the constellation in the winter months, be sure to mark the 7th-17th December in your diary — the period of the annual meteor shower known as the Geminids. These meteors appear to come from a point in the sky near Castor and, at their peak, you may see a display of over 100 in an hour! This meteor shower occurs as the earth travels through the trail left behind by an asteroid. Rock and dust burns as it enters Earth’s atmosphere and produce the sparks of falling light that we know as shooting stars.
For now, as the days continue to get longer, don’t forget to catch the twins before they leave for their summer holiday!
All pictures sourced from Bing’s image search, filtered to a licence of “free to share and use” unless otherwise stated.
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