A second close-passing comet

Climbing northward out of the constellation Cancer is 41P Tuttle-Giacobini-Kresák, and among this year’s comets it will be the one that climbs closest to the north pole of the sky.

As yet, it’s a faint telescopic target – magnitude perhaps 10 – but it is destined for one of its best appearances: in April it will be at a perihelion close outside, and steeply north from, the April part of our orbit.

Its tail isn’t likely to appear as long as in the picture, but note its relation to the point marked “Anti-Sun.”  Comets’ tails are blown outward by the Sun’s radiation pressure and the solar wind.

The Planetary Science Institute has a research campaign (http://www.psi.edu/41P45P46P) for which it invites all amateur and professional astronomers to contribute their images of three comets making close approaches to Earth: 45P Honda-Mrkos-Pajdušáková, 41P Tuttle-Giacobini-Kresák, and 46P Wirtanen.

Wirtanen’s arrival will be in late 2018.  The other two are the ones we’ve just greeted in the early months of this year.  I’ve added fuller information and diagrams for both of them to the growing comet section of “Astronomical Calendar 2017,” found from the link above.