In Our Skies: A good opportunity to view December’s comets

Up through the latter part of the 20th century, many – indeed, a significant majority – of comets were discovered by dedicated amateur astronomers who regularly searched the skies for these fuzzy visitors from the outer solar system.

While photographic comet discoveries became more commonplace as the century wore on, the visual searches by the amateurs continued to hold sway.

With the advent of the sky survey programs that primarily search for Earth-approaching asteroids – and that utilize sensitive electronic detectors and automated motion-detection software – in the late 1990s, these began to discover scores of comets long before they became bright enough to be detected by the visual comet hunters.

With only five comets having been discovered visually within the past 15 years – and the most recent such discovery taking place as long ago as November 2010 – it was beginning to look like such visual comet discoveries were a thing of the past.

But not entirely . . . a handful of dedicated comet hunters around the planet have continued their quests in the face of the overwhelming odds against them.

One of these – and a friend of this author’s – is Don Machholz in northern California, who discovered his first comet in 1978 and 10 more since then, including one which became an easy naked-eye object in 2004-05.

On the morning of Nov. 7, 2018, he discovered his 12th comet, traveling through the stars of the constellation Virgo. A few hours later this same comet was independently discovered by two Japanese amateur astronomers, both of whom were using electronic cameras: Shigehisa Fujikawa and Masayuki Iwamoto.

Both individuals had also discovered comets in the past; Fujikawa had visually discovered six comets dating back to the late 1960s. The new comet was given the rather cumbersome name of Machholz-Fujikawa-Iwamoto.

The new comet was bright enough to detect with binoculars when it was discovered, but within two weeks of its discovery it began to pass between the Earth and the sun and disappeared into the dawn. It passed 62 million miles from Earth on Nov. 27 and 36 million miles from the sun – Mercury’s distance – this past Monday, Dec. 3.

At this time, it is making a brief appearance in the western sky during dusk as it travels through the stars of the constellation Scutum north of Sagittarius; according to the latest information at this writing it may possibly be detectable with binoculars but will likely not become very bright.

While the prognosis for a bright display from this newest comet is thus not very good, another comet in our skies has already begun to attract a lot of attention.

This comet was discovered back in 1948 by Carl Wirtanen, at that time an astronomer at the Lick Observatory near San Jose, California. The comet was a rather dim object with an orbital period of slightly under 7 years, however some close approaches to Jupiter, and its gravitational field, during the intervening years have brought it closer to the sun and Earth and have shortened its orbital period to 51Ž2 years.

Since about the mid-1980s it has often become bright enough to detect with backyard telescopes, although it has never been especially bright or noteworthy.

This year is different, however. When Comet Wirtanen is closest to the sun it is 98 million miles from our parent star, just outside Earth’s orbit. When it passes through that point this year, which it will do on this coming Wednesday, Dec. 12, Earth will be at that same location in its orbit.

The net result is that, on Dec. 16, Earth and Comet Wirtanen will pass only 7.2 million miles from each other, one of the closest cometary approaches to Earth in recent history.

At this writing Comet Wirtanen is already visible to the unaided eye – at least, from dark rural sites – as a dim large fuzzy cloud larger than the apparent diameter of the full moon.

It should grow brighter and larger over the coming days as it draws closer to Earth, and on the nights around closest approach should be rather easily detectable with the unaided eye, although, again, it will look like a large fuzzy cloud.

Comet Wirtanen is currently traveling northward through the stars of the constellation Cetus but enters Taurus – now in our eastern sky during the evening hours – within a couple of days. On the night of its closest approach it will be conveniently located between Taurus’ two prominent star clusters, the Pleaides and the Hyades. Thereafter it continues traveling northward through the constellations of Perseus and then Auriga and passes close to the bright star Capella in Auriga Dec. 23.

Unfortunately, the moon, which will be just past its First Quarter phase at the time of Wirtanen’s closest approach and then full a week later, will interfere with comet viewing after the approach.

By the time we have a dark sky in the evening again – towards the end of this month – Wirtanen will be pulling away from Earth and fading, although it should remain visible with binoculars, and then backyard telescopes, for a few more weeks.

Comet Wirtanen will never approach Earth this closely again, and in fact some forthcoming approaches to Jupiter will move it farther out into the solar system away from our planet. But other comets will continue to pass by from time to time; indeed, there are a couple of comets that have already been discovered by the automated surveys that have the potential of becoming at least somewhat bright over the near- to intermediate-term future.

As always, this column will report on these objects at the appropriate time.

Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere.