The constellation Twins (Gemini - Gem)


A multimedia constellation

The constellation of Gemini appears majestic, inextricably linked to the nearby Taurus and Orion below, in a fascinating set of truly breathtaking star clusters: it does not appear at all diminished compared to the magnificent Orion, precisely because it has three stars of first magnitude and a cluster of stars a little 'less bright and therefore not very visible in the bright city skies. I was talking about three bright stars: said of the first two, the third one, called Alhena (γ Gem), appears in all its splendor, if we know where to find it...


We are talking about a zodiacal constellation and then as usual we see the apparent path of the Sun in the sky inside it, along that imaginary line called ecliptic: we can see that this passage takes place between June 21 and July 20, where these two dates may change slightly because of the perturbations of the Earth's orbital motion around the Sun, which are therefore reflected on the apparent motion of the diurnal star. We would like to thank once again the designers of the Stellarium program, thanks to which I can take pictures and ideas of great utility!

As on the occasion of other zodiacal constellations, I remember that in the 70s the Republic of San Marino had issued a nice and amusing collection of stamps on the theme of the Zodiac: as a very recent astronomy enthusiast I immediately went to the Central Post Office of San Silvestro in Rome to buy the 12 stamps. I also remember that the whole thing was not cheap at the time, but for passion you do this and more! Unfortunately after so many years I don't know what happened to them anymore, but I'm satisfied with their photograph found on the internet.


The representations of Gemini


I said at the beginning that the Gemini are the Dioscuri Castor and Pollux: about their birth there are many contrasting stories on which modern tabloids would talk for months. They are the sons of Leda, with whom Zeus had joined under the appearances of a swan, but it must be added that that same night the young girl had also rightly been with her legitimate husband: after the canonical nine months four little babies were born. Without the possibility of DNA tests, it seems that Pollux and Helen (yes, she, the one who, when she grows up, will unleash the Trojan War) were the immortal sons of Zeus, while Castor and Clytemnestra were the legitimate and mortal sons of Tindaro, the spouse of the beautiful Leda.

That they were twins was beyond doubt, but on the rest of the story we drop the classic pitiful veil: we are content to see them immortalized by Bayer in his Uranometria, by Hevelius in his upside-down work and more recently by Stellarium. 

In the Uranometria our people were engaged in musical activities

while according to the astronomer Hevelius they appear modestly from behind

and finally, according to the Stellarium program, they appear dressed in a classic tunic.

A dozen big stars


Looking at the little picture next to it with the eye now trained by the previous episodes, you can already imagine that in this constellation there are many stars with a diameter greater than 50 times that of the Sun: clicking as always on the picture will appear the diagram I made, in which I did a little bit of effort to insert 13 stars in a kind of big snake, starting from the biggest one on the top left (6 Gems as many as 290 times our Sun!), passing through 41 Gem (234 times), then η Gem (157 times) and then again μ Gem (only 104 times) and then descending to the threshold that I self-imposed, of 50 times the solar ray.


Note the presence of two stars of spectral class G as our Sun, Mebsuta and Mekbuda, having a ray respectively 94 and 74 times the solar one. However the star 6 Gem deserves a photo with a standard distance (for this kind of celestial monsters) of 10 UA, about the distance of Saturn from the Sun: as we see in the photo, this star of 10 UA appears a pleasant orange color, but 13 and a half degrees large. I remember that instead, being close to the planet of the rings (ideally aboard the Cassini spacecraft), the Sun appears with a diameter of just 3 arcminutes!



Audio Video The constellation Twins (Gemini - Gem)
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