06-24 December 2018
46P/Wirtanen is a short (5.4 years) period comet which was discovered photographically by Carl Wirtanen in 1948 at the Lick Observatory, California.
In early December 2018, it passed northwards from Eridanus into Taurus, heading towards Auriga, and became visible to observers in the northern hemisphere. It brightened in the winter sky, reaching perihelion on 12 December and coming closest to the Earth on 16 December, at a distance of approximately 11m km. On this date it was some 160m km from the Sun and was also at its brightest. On 24 December, it passed close to the bright star Capella.
Finder chart for the comet (by Sky & Telescope magazine).
Images by Members of OASI
Unfortunately, cloudy nights around the date of closest approach severely restricted observing opportunities.
- Mike O'Mahony. 06 December 2018. Meade 235 mm f/10 SCT on HEQ5 mount, Canon 60Da camera, 8 s exposure at ISO 2500.
- Martin Cook. 21:00 UT, 07 December 2018. Canon 1100D, undriven, 10 s exposure at ISO 1600. Strong wind and light pollution compromised the image.
- Andy Gibbs. 21:45 UT, 07 December 2018. Meade LX200 200 mm SCT, Canon 1200D camera, 60 s exposure at ISO 800.
- James Appleton. 22:06 UT, 07 December 2018. Canon 6D Mk II camera with 300 mm lens, 1 s exposure at ISO 16,000.
- Mike O'Mahony. 19:15 UT, 24 December 2018. Meade 235 mm f/10 SCT on HEQ5 mount, Canon 60Da camera, 30 s exposure at ISO 4000.
- James Appleton. 22:38 UT, 24 December 2018. Canon 6D Mk II camera with 300 mm lens, 1.6 s exposure at ISO 20,000. The star nearest to the comet is H26267, magnitude 7.5, slightly over 5° distant from Capella. The star is of spectral class K, and an orange tinge is evident on zooming into the image.
Alan Smith's all-sky camera was sensitive enough to capture the comet. (This was an unexpected bonus as the camera was not designed to capture faint objects!) The following montage shows the motion of the comet against the background stars during the period 06-13 December 2018. All images have an exposure of 150 s at F2.8, ISO 800 with a 4.5 mm lens.
- The night of 11 December was cloudy, so images taken then show low contrast.
- At 17:32 UT on 11 December, the comet appeared just above a neighbour's chimney, which appears as the over-exposed protrusion to bottom-left of the image.
- Cloud cover prevented capturing an image on the night of 12 December.
- The images below cover approximately the same region of background sky. Due to the distorting effect of the fisheye lens, it proved impossible to make coverage of the images identical.