Comets are notoriously difficult beasts to predict how bright they may become so any prediction of their magnitude in Nightscenes has to be taken with this in mind. Still it is worth including any known comet that may have a chance at becoming visible in binoculars or even naked eye and, at the time of writing the book, two of them occur for the second half of 2018. So we have Comet 21P/Giacobini-Zinner and Comet 46P/Wirtanen to look forward to with the latter potentially becoming naked eye!.

Comet  21P/Giacobini-Zinner


Comet  21P/Giacobini-Zinner now lies in the morning sky moving into  into Monoceros passing close to the star cluster M50 on October 8th. It moves into Canis Major passing to the left of Sirius on October 14th/15th and has faded to mag 9.1 on October 26th at the end of the second chart (left)

Our next comet is Comet 46P/Wirtanen which could become a naked eye comet - well we can hope! We pick it c-Wirt-1.jpgup when it is mag 9.6 on October 1st in the morning sky very low in the constellation of Fornax. It is moving slowly southwards so not making things better but it should begin to brighten through October and on November 1st it should be mag 7.3 and visible in a binocular. Over the next two days it starts to brighten by a full magnitude to 6.3 and also ends its southwards motion turning northwards. Note this is just from the Earths perspective, as it really doesn’t do a sharp turn in space, it is the motion of both comet and Earth that can make things look a little strange.

Now it speeds up moving back up through Fornax and into Cetus, passing close to Pi Ceti on December 4th when the comet could be mag 4.5 and so possibly visible to the naked eye. It passes into Eridanus then back into Cetus before reaching perihelion on December 12th lying close to Omicron and Xi Tauri.

The chart below shows how much the comet moves in just twenty days as it races through Taurus, dips into Perseus, into Auriga then ends the year in Lynx! As it does so it is closest to the Earth on December 16th but don’t worry, it should be 7.2 million miles away so won’t collide with us. It is because it is ‘close’ as it passes that it moves quickly through so many constellations. 46P/Wirtanen is also near to M45 on that evening but the downside is the Moon is a day past First Quarter phase. 46P/Wirtanen lies close to the ‘kids’ asterism on c-Wirt-2.jpgDecember 22nd then the next evening it lies close to Capella (the second comet to do so this year!) and is still a 4th mag comet so let’s hope the Full Moon on the 22nd doesn’t spoil the view too much. 46P/Wirtanen races away and lies close to 15 Lynx on December 31st but is now beginning to fade and should be mag 5 as we enter into 2019.

Fingers crossed it does indeed end up being a bright comet!

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