Winter solstice, the Pleiades and a meteor shower
In December, not only Advent wreaths and light chains are illuminated – there is also a lot going on in the sky. Because now one of the stars in the night sky can be observed especially well: the Pleiades. In the middle of the month, a cosmic dust cloud also gives us an abundant shower of shooting stars: The meteor shower of the Geminids reaches its peak.
December is the darkest month of the year: The sun is only in the sky for about eight hours, it is dark for 16 hours. And our star no longer rises particularly high: even at noon, it is only about 16 to 17 degrees above the horizon in Germany. On 22. December has reached the darkest day of the year – the sun rises only around 08:00 o’clock and sinks already around 16:15 o’clock again under the horizon. It is even darker due to the fact that on this day there is also a new moon.
But at the same time the 22. December also a turn for the better: the winter solstice. From this day on, the days become longer again and the next one shorter. At the same time, the places where the sun rises and sets are gradually moving further west and east again. The arc that the sun seems to traverse in the sky during the day becomes larger again. It is therefore no coincidence that the winter solstice was celebrated in almost all early cultures and played a role in religions and rituals. Our Christmas was also intentionally placed in this time by the early church fathers.
NASA, ESA, AURA/Caltech
High season for the Pleiades
December is a good month to observe the Pleiades. Also known as the Pleiades, this open star cluster is visible to the naked eye in the night sky. It lies in the constellation Taurus, right above the V-shaped bull’s head. Even without binoculars you can see the five brightest stars of this cluster. With a little search and from a dark location two more fainter stars can be spotted.
In reality, however, the cluster of stars about 444 light-years from Earth consists of more than 3.000 stars, but most of them are too faint to be seen without telescope. The Pleiades consist of rather bluish, still very young stars – they were formed within the last 100 million years, so by galactic standards they are still real children.
Seen from the earth, the star cluster has an extension of two angular degrees – it is three times as big as the moon – and therefore very clearly visible as a bright spot. So it’s no wonder that people in the Stone Age observed this striking phenomenon in the sky. In many ancient cultures, including Egypt and Mesopotamia, the course of the Pleiades was followed to determine important dates in the course of the year – especially the time of sowing in spring and the end of the harvest in autumn. On one of the most important finds of the European Bronze Age, the Nebra Sky Disk, the Pleiades is probably immortalized as a group of points.
Shooting star shower: The meteor shower of the Geminids
On 13.-14. December there are again good prospects for shooting stars, because then the climax of the Geminid meteor shower occurs. The shooting stars seem to come from the constellation of the Gemini, so they can be observed already from 21:00 in the evening, when this constellation becomes visible in the sky. Up to a good 100 meteors can fall per hour in the process. The Geminids are known to produce many bright shooting stars – a look is worthwhile despite the cold weather.
Unlike the Perseids and many other meteor showers the cause of the Geminids is not the dust tail of an active comet. Instead, the dust cloud the Earth is passing through these days goes back to the asteroid Phaeton. On its orbit around the sun, it drags a trail of debris behind it that is much more compact than the dust tail from the comet. Researchers suspect that this debris was created when Phaeton collided with another celestial body. Possibly it is also the nucleus of an extinct comet – one is not sure about that.
Planets: Jupiter moves backwards
Jupiter is the dominant planet in the sky in December. It can be seen in the second half of the night in the constellation Leo and seems to stand almost still. Then, from the 10. December it reverses its normal direction of movement – it becomes retrograde. Of course, in reality, the planet does not change its slow orbit around the sun. It only appears to be going backwards in the night sky because the earth is currently overtaking it on its inner orbit around the sun. Relative to us, Jupiter therefore appears to move backwards for a short time.