This zodiac constellation is probably known since 6,500 years as the Bull. Aldebaran symbolizes the eye of the Bull; its horns are formed by the stars β and ζ Tauri. β Tauri is located exactly on the border to Auriga, where it is referred to as γ Aurigae.

T Tauri can be found 1.5° west of ε Tauri, above the Hyades. If the star is bright enough, you can see it quite easily, but often it is too faint for binoculars. Still, it’s worth trying – T Tauri is the namesake of a class of very young stars, where nuclear fusion is still irregular. Its brightness varies unpredictably from 8.4 to 13.5m. It illuminates NGC 1555, from which it also emerged, but that nebula is visible only through the telescope. NGC 1555 is also known as “Hind’s Variable Nebula”, both its form and its brightness change again and again.

M 1 is also well known as the Crab Nebula. It appears in binoculars as a small 4 × 6 arcmin large patch of light 67 arc minutes northwest of ζ Tauri. M 1 is the remnant of the supernova which was observed for the first time on July 4th, 1054 by Chinese astronomers, and was visible for several months even in the daytime. The gas layers, which were then repelled from the star, expand today at 930 miles per second (1,500 km/s). The star itself is collapsed to a neutron star only 6.2 miles (ten kilometers) wide. This pulsar is the fourth-brightest object in the sky – at least for radio astronomers.

The Plejades have the catalog designation M 45 and are famous as one of the most impressive open clusters for binoculars. In the vernacular they are known as the Seven Sisters, which probably goes back to ancient numerology: When it is dark enough to see the seventh star of the Pleiades, you can see also the eighth. Up to ten stars are visible under good conditions, experienced observers also claim to have recognized up to 18 stars. It is sometimes speculated if one of the stars was once darker, and sometimes really only seven stars were visible, but ancient Chinese texts also report more than seven stars.

Die Plejaden sind ein sehr ausgedehnter Sternhaufen, um den das schwache Schimmern eines Reflexionsnebels erahnbar ist.
The Pleiades – a large star cluster embedded in a reflection nebula.

The nine brightest Pleiades stars are spread over an area of 1° diameter, which corresponds to twice the full Moon diameter. In encounters with the Moon, the tremendous expansion of the Pleiades can be seen. The real diameter is estimated to be at seven light-years, although the exact distance of the Pleiades is not known exactly – the satellite Hipparcos yielded a distance of only 360 light-years, while newer measurements indicate some 440 light-years, which agrees better with older measurements. The exact distance of this cluster is particularly interesting, because the measurements of more distant objects are based on the distances of star clusters like the Pleiades. Only three other clusters are even closer to us – Collinder 285 (the Big Dipper, 70 light-years), the Hyades (150 light-years) and the Coma Cluster (260 light-years).

The 80 to 100 million year old star cluster is about five times larger than its striking core area. About 300 stars belong to it. Under good conditions, you can recognize a nebula around the brighter Pleiades stars. It is a reflection nebula through which the Pleiades cluster passes at the moment, and not the remnants of the formation of the cluster as is occasionally still told in older literature. In order to successfully observe it, you definitely need clean optics – otherwise you will see a light shimmer around all the brighter stars.

Although NGC 1746 has a catalog name and is visible to the naked eye as a 40 arcmin large nebula, this cluster does not exist – It is an “optical double star cluster”. It consists of the 28 minutes of arc large NGC 1750 at 1,640 light-years away and the eight arcminutes wide NGC 1758 which is 2,200 light-years away. By sheer coincidence, the two star clusters appear to overlap each other, even though they are just like an optical double star just by chance on the same line of sight. Such errors are quite common in astronomical catalogs, and therefore it is generally more useful to speak of entries instead of objects in catalogs.

With a diameter of 5.5°, Hyades is beyond the field of view of every telescope, while binoculars show a myriad of stars. Currently, this open cluster is 150 light-years away, but in 50 million years it will only be visible in the telescope – because of the rotation of the galaxy and the proper motion of the stars, it will appear then only 20 minutes of arc great. The V-shaped center has a diameter of eight light-years. Since even more distant stars as κ, ι and υ Tauri belong to the Hyades, the overall diameter is more than 60 light-years. The Hyades arose about 400 to 700 million years ago.

The stars of the Hyades all seem to move towards Betelgeuse in Orion, which is of course a projection effect. 100 more stars visible for the naked eye are moving in the same direction as the stars of the Hyades. They form the Hyades Moving Group and have a common origin in a single, vast gas cloud. The mean age of these stars is 600 million years, so they have orbited the galaxy since their birth three times. The members of the Hyades Moving Group include the open cluster M 44 in Cancer (“Praesepe”), but also Capella in Auriga and Cor Caroli, the brightest star in the constellation Canes Venatici.

Our much older Sun is just by chance between the stars of the Hyades Group. Also Aldebaran (α Tauri) belongs neither to the star cluster of the Hyades nor to the Moving Group, although the brightest star of Taurus seems to stand in the middle of the Hyades. Instead, it is a red giant at a distance of only 65 light years. This old star has forty times the diameter of our Sun, and its position changes by 3.5 arcminutes within a millennium.

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