A Piece of a Comet

This picture just might lure you to go out early very early on a late-summer morning and look at the pre-dawn sky, in which you just might be able, with telescope or large binoculars, to see a comet in the midst of the stars of Gemini.

Or you may have to settle for seeing it with the mind’s eye. It’s interesting enough: it’s actually just the surviv fragment of a comet that broke up.

Don Machholz is a California amateur astronomer who has discovered 11 comets – more, by visual means (as opposed to operating photographic or automated systems), than any other living person. (Bill Bradfield of Australia, who died last year, was the sole discoverer of 18; W.R. Brooks was sole or joint discoverer of 21 in the late 1800s, and Jean-Louis Pons of 37 in the early 1800s.)

Comet 141P Machholz 2 (the 141st known comet of the periodic kind, and Machholz’s 2nd of that kind) was discovered in 1994. It is one of the close-in comets, with a short orbit of only 5.25 years, bringing it in past Earth to a perihelion (nearest point to the Sun) that is a quarter of the way inward from our orbit toward the Sun.

In the weeks after the comet was discovered, others were noticed traveling along near it. What had happened was that it had broken apart. The five visible pieces were labeled A, B, C, D, E. Piece D had two bright centers within its “coma” or bright cloud of dust, suggesting that it too was about to divide, and perhaps the breakup had resulted in other pieces too small to be seen.

The break-up may have happened at one of the comet’s previous undiscovered visits. It happens; a comet’s nucleus is a fragile clump of matter, and when it ventures near to the Sun the tidal force – the difference between the Sun’s gravitational pull on the near and farther sides – can be great enough to wrench it apart.

Five years later, in 1999, 141P duly returned – or, rather, only component A did, and then a fainter D. In 2005 the only piece seen was calculated to be the original, A.

This time, 141P-A has arrived somewhat too early for our convenience.

Adapted from the “Comets” section of Astronomical Calendar 2015.

It crosses inward over the August part of our orbit, but it did so in the middle of July. The result is that we have to look out ahead to it – that is, to the right (west) of the Sun, in the morning sky. Now nearest to the Sun, it shines as brightly by reflected sunlight as it can, but it is a whole astronomical unit (Sun-Earth distance) away from us. It may be at about magnitude 11, which is far too faint for the naked eye.

And this is about the last chance with telescopes of amateur size. Traveling, on the inner part of its elliptical orbit, much faster than Earth is, it is getting farther away.

NOTICE. If I keep using so much time on composing these blog posts – every time, more time than I expected – I’ll never get Astronomical Calendar 2016 done. So, from now until that’s achieved, I shall make them minimal.