December 2021 – What’s Up!

Week of 27th December

  • Astronomical twilight ends at 18:08 UT at the start of the week and at 18:13 UT by the end of the week
  • If the sky ever clears, it will be possible to view six planets in a line this week, starting with Mercury (mag -0.7) closest to the southwest horizon just after sunset at around 16:05 UT, next is Venus (-4.4), then Saturn (+0.7) and Jupiter (-2.2). As the sky reaches astronomical darkness, look for Neptune (+7.9) in the south and Uranus (+5.7) in the southeast
  • For the early risers, add Mars (+1.5) to the planetary tally as it rises in the southeast at around 06:15 UT this week. It will be joined by the waning crescent Moon on Friday morning. To complete the solar system line up, spot the eighth and final planet by looking towards your feet!
  • The Moon is Last Quarter on Monday and New on Sunday
  • The Sun currently has seven active regions: AR 2908, 2912, 2915, 2916, 2917, 2918 & 2919. The sunspot number is 128
  • There are no visible evening ISS passes this week

Week of 20th December

  • Astronomical twilight ends at 18:04 UT at the start of the week and at 18:08 UT by the end of the week
  • The Winter Solstice is on Tuesday, which will be the shortest day in the Northern Hemisphere and the first day of astronomical winter. The Sun will reach its lowest point in the sky at -23.5° declination. From this point on, it will be rising higher and higher and the days will lengthen as we head back towards summer – Happy Solstice!
  • The Ursid meteor shower peaks through Tuesday night with its radiant in the constellation of Ursa Minor. It is not a particularly spectacular shower, with a ZHR of only around 10 meteors per hour, and the bright Moon is a hinderance, but you might spot a meteor caused by the debris deposited by comet 8P/Tuttle
  • The planets Venus (mag -4.6), Saturn (+0.7) and Jupiter (-2.2) continue to adorn our evening sky in a line over the southwestern horizon around sunset
  • The Moon is Waning Gibbous all week
  • The Sun currently has six active regions: AR 2906, 2907, 2908, 2909, 2910 & 2911. The sunspot number is 117
  • There are no visible evening ISS passes this week

Week of 13th December

  • Astronomical twilight ends at 18:02 UT at the start of the week and at 18:04 UT by the end of the week
  • The week starts with the ‘King’ of meteor showers, the Geminids. Its ZHR is upwards of 120, so can be spectacular. Unfortunately, the waxing gibbous Moon will drown out the fainter meteors this year. The shower is active from 7th to 17th December, with its peak on Monday night. Unusually for meteor showers, it is caused by debris deposited by an asteroid, Phaethon
  • Venus (mag -4.7) reaches its highest altitude in our evening sky on Monday at about 13° above the southwestern horizon at 16:30 UT. Saturn (+0.7) and Jupiter (-2.2) complete a beautiful planetary twilight line up
  • Comet C/2021 A1 Leonard, currently grazing our southwestern horizon at sunset, is about to sink lower, becoming visible only from more southerly latitudes by the middle of the week. It reaches perigee on Monday and perihelion on 2022-01-03
  • The Moon is Full on Sunday
  • Following an increasingly active year, the Sun currently has no active regions, though a new sunspot is emerging around the oncoming limb
  • There are no visible evening ISS passes this week

Week of 6th December

  • Astronomical twilight ends at 18:02 UT at the start of the week and at 18:02 UT by the end of the week
  • The waxing Crescent Moon parades past the naked eye planets this week, near to Venus (mag -4.7) on Monday, Saturn (+0.7) on Wednesday and Jupiter (-2.3) on Thursday
  • Comet C/2021 A1 Leonard, currently visible in our pre-dawn sky in binoculars at around mag +7, will become visible in our evening sky this week. Look 40 to 50 degrees further west of Venus at a similar altitude at around 16:30 UT to try and spot the comet. Predictions suggest that it could even become naked eye visible by the end of the week
  • The Moon is First Quarter on Saturday
  • The Sun currently has 3 active regions: AR2901, AR2902 and AR2904. The sunspot number is 35
  • There are visible evening ISS passes this week as follows:
    Monday: 16:59, W to SE, max 46° and 18:37, WSW to SSW, max 12°
    Tuesday: 17:49, W to S, max 18°
    Wednesday: 17:01, W to SSE, max 25°
    Friday: 17:04, WSW to SSW max 12°
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