The twins Castor and Pollux of Greek mythology were the inspiration for this constellation, and its two brightest stars are named after this pair of twins. Castor (α Geminorum) is a six fold star only 51 light years away and with a total of 1.6^m slightly darker than the 1.2^m bright and 33.7 light-years away Pollux (β Geminorum). In the lower half of the constellation, the two reddish stars η and μ show a nice color contrast to the bluish-white γ Geminorum.

Two planets in our solar system were discovered in the Twins – Uranus was observed in the vicinity of η for the first time in 1781, and Pluto in 1930 in the vicinity of δ.

In the center of the constellation, ζ Geminorum can be found – one of the brightest variables of the Cepheid type. Its brightness varies within 10.15 days between 3.6 and 4.2^m. Its period is not quite constant, but increases each year by 3.6 seconds. 1,200 light years separate us from it.

It is still unknown why the brightness of BU Geminorum varies irregularly between 5.7 and 7.5^m. Its brightness changes only slowly – perhaps it is therefore classified sometimes as an eclipsing binary, although its light curve is irregular. The distance of the star is unknown.

M 35 is easy to find 2.5° northwest of η Geminorum. Only about half a dozen stars can be resolved with binoculars, the remaining stars blur into a shimmer. The open cluster has a diameter of about 40 light years – at a distance of 2,600 light years it appears as large as the full Moon.

NGC 2392 is one of the most distant open clusters – 14,000 light-years separate us from it. With a brightness of only 8.6^m and a diameter of five minutes of arc it is a target for larger binoculars. The rather old star cluster is located near the rim of our galaxy and can only be observed because its light is hardly attenuated by interstellar dust clouds. It was formed 800 million years ago.