December 2020 What’s Up!

Week of 28th December

• Astronomical twilight ends at 18:09 UT at the beginning of the week and at 18:14 UT by the end of the week
• The Quadrantid Meteor Shower peaks on Sunday, with a maximum ZHR (zenithal hourly rate) of 120 meteors. The radiant is in the old constellation of Quadrans Muralis, hence the name; however, Quadrans Muralis is no longer recognised, so the radiant appears in the modern day constellation of Bootes. The parent body responsible for the shower has been identified as asteroid 2003 EH1
• The Earth passes through perihelion at 13:50 UT on Saturday, when it will be at its closest point to the Sun on its annual elliptical orbit. It will be 0.98 AU from the Sun or 147 million km. This is in contrast to its distance of 152 million km when at aphelion. Consequently, the Sun will appear about 3% larger, though it will be extremely difficult to notice this difference!
• The Moon is Full on Wednesday
• The Sun currently has two active regions, AR 2794 & AR 2795 – the sunspot number is 31
• There are no visible ISS evening passes this week

Week of 21st December

• Astronomical twilight ends at 18:05 UT at the beginning of the week and at 18:08 UT by the end of the week
• The Great Conjunction is on Monday, when Jupiter (-2.0) and Saturn (+0.6), will be separated by just 6 arcminutes. This is the closest that they have appeared since 1623. Due to their orbital mechanics, Jupiter ‘undertakes’ Saturn roughly every 20 years, so conjunctions are not particularly rare. However, the inclination of the planets’ orbits with respect to the Earth means that they are not often this close together. Combine this with the angular distance of the planets from the Sun, meaning that some conjunctions are too close to the Sun to be observed and you will see that this is a rare event. The next Great Conjunction will be in 2080, so if there is a clear sky, take the opportunity to enjoy this rare view of the two gas giants in the same field of view of your binoculars or telescope. You can also look in the days before and after the 21st as the two planets pass eachother
• Monday is also the Winter Solstice, marking the lowest point the Sun appears in the sky at a declination of -23.5°. It is the shortest day of the year and the start of winter in the Northern Hemisphere. Christmas borrows its date from this pagan festival. Nowadays Christmas is a few days after the Winter Solstice due to the Leap Year only being introduced in the 16th Century. Before the introduction of the extra leap days, the calendar and the astronomical event slowly drifted apart over the years
• The Ursid Meteor shower peaks on Tuesday. It is not a particularly active shower, with a peak rate of around 10 meteors per hour. The shower’s radiant is in Ursa Minor and the meteors are caused by the Earth passing through the stream of debris created by comet 8P/Tuttle
• The Moon is First Quarter on Monday
• After a recent active period, the Sun is now quiet with no active regions – the current stretch is 1 day
• There are no visible ISS evening passes this week

Week of 14th December

• Astronomical twilight ends at 18:02 UT at the beginning of the week and at 18:04 UT by the end of the week
• Watch Jupiter (-2.0) and Saturn (0.6) in the southwestern evening sky just after sunset as they approach eachother through this week, culminating in The Great Conjunction on Monday 21st December. They start the week 47 arcminutes apart and by Sunday, will have just 9 arcminutes of separation. If there is a clear sky, take the opportunity to enjoy this rare view of the two gas giants in the same field of view of your binoculars or telescope
• There is a total solar eclipse on Monday. Don’t get too excited though, it will not be visible from Marlborough! Observers in Chile and Argentina will witness this spectacular solar system syzygy between 13:34 and 18:53 UT, with totality expected to last for 2 minutes and 10 seconds at the point of greatest eclipse. Check on line for a live feed of the eclipse
• The Moon is New on Monday
• The Sun currently has two active regions: AR 2790 and AR 2792, with a combined sunspot number of 24
• There are no visible ISS passes this week

Week of 7th December

• Astronomical twilight ends at 18:02 UT at the beginning of the week and at 18:02 UT by the end of the week
• The Geminid meteor shower peaks on Sunday night. As the Earth passes through debris deposited in space by asteroid 3200 Phaethon, we can enjoy one of the finest cosmic fireworks shows of the year! The Geminids can produce up to 110-120 meteors per hour at its peak, which occurs this year at about 01:00 UT on Monday 14th. The Moon is New on the 14th, so observing conditions will be perfectly dark. All that is needed is no cloud. Even that is not a problem this year as the new Blackett Observatory Radio Meteor Detection System is now live and will be listening out for meteor ‘pings’, whatever the weather
• The Moon is Last Quarter on Tuesday
• The Sun currently has three active regions: AR 2785, AR 2786 and AR 2790, with a combined sunspot number of 42
• The ISS makes multiple evening passes as follows:
  Monday: 18:07, W to S, max 18Â
  Tuesday: 17:19, W to SSE, max 25Â
  Wednesday: 16:31, W to SE, max 34Â
  Thursday: 17:22, WSW to SSW, max 12Â
  Friday: 16:33, W to S, max 18Â