December Skies

Some things that may be of interest during the festive month of December:

1st, Arcturus (figure 1) is visible in both the dusk and dawn skies. In the evening, it will become visible around 17:07 (GMT) as the dusk sky fades, 14° above Western horizon. It will sink towards the horizon, setting 2 hours and 26 minutes after the Sun at 18:52 (GMT). In the morning, it will rise at 03:14, 4 hours and 15 minutes before the Sun and reach an altitude of 30° above the Eastern horizon before fading from view as dawn breaks around 06:48.    Arcturus is approximately 37 light years from Earth. It is the brightest star in the constellation of Boötes, the 4th brightest in the night sky and the brightest in the Northern celestial hemisphere (figure 2).

Figure 1: Arcturus in Bootes.

Figure 2: Optical image of Arcturus (DSS2 / MAST / STScI / NASA).

Gemininds:

Geminids is the King of the meteor showers. Capable of producing 120 multicoloured meteors per hour at its peak. Produced by debris from the asteroid 3200 Phaethon (figure 3 & 4), which was discovered in 1982. The shower appears between December 7th and 17th. It will peak on the night of 13th and morning of the 14th. The Moon will be shining however, the number of meteors should still give a good show, providing viewing from a dark location.

Figure 3: Radar image of 3200 Phaethon, Arecibo, December 17th, 2017.

Figure 4: The elliptical orbit of 3200 Phaethon crosses the orbits of Mars, Earth, Venus and Mercury.

  • Rating: Very Strong
  • Degrees: 138º (Looking Southeast)
  • Note: Richest of the annual showers, with slow meteor and good bright events.

21st will be the December or winter solstice (figure 5), it is the shortest day of the year in the Northern hemisphere.

Figure 5: December or winter solstice.

Ursids:

The Ursids meteor activity begins annually around December 17th for approximately one week until the 25th/26th. This meteor shower is named for its radiant point which is located near the star Beta (β) Ursae Minoris (Kochab), (figure 6) in the constellation Ursa Minor.

Figure 6: Location of β Ursae Minoris.

  • Peak Date: 22nd December
  • Rating: Strong - Approximately 10 per hour
  • Degrees: 217º (Looking Southwest)
  • Comet: 8P/Tuttle (figure 7)
  • Note: Under-observed shower which had produced outbursts in 1945, 1982 and 1986

Figure 7: Comet 8P/Tuttle, discovered by Horace Parnell Tuttle on January 5th 1858.

I wish all sky watchers a very enjoyable Christmas 2019 and good viewing in 2020.

WARNING: Never attempt to view through binoculars, telescope or any optical aid an object near to the Sun. Also, never attempt to view the Sun unaided, doing so may result in immediate and permanent blindness. Always use astronomical approved viewing equipment.

The Stellarium software will assist greatly in locating objects in the sky.

Mark R Smith FRAS

Physicist

Nuclear Fusion Physics

Astrophysics