Surprising and beautiful, comets are a favorite of backyard astronomers. The rarity of bright comets makes them exciting sky events and their unpredictable nature adds immeasurably to their appeal. Some comets are more predictable than others. Periodic comets are objects in elliptical orbits around the sun that have a known orbital period. We can predict their return to our sky rather accurately. In addition to the names of their discovers, they carry numerical designations that indicate their order of discovery. Edmund Halley was the first to predict the return of an orbiting comet and the object named for him bears the designation 1P.

While periodic comets return on a regular schedule, their distance from Earth at closest approach varies greatly. We are about to experience the close approach of three comets in succession over the next 20 months, a very rare occurrence. The first of those close approaches comes this month when Comet 45P/Honda-Mrkos-Pajdu Sakova passes 7.4 million miles from Earth on Feb. 11. Well see this comet brighten considerably as it moves rapidly across our sky. In just two weeks it will go from a morning object in Aquila to an evening object in Coma Berenices. It will be a fine binocular object and has the potential to be visible to the naked eye at its brightest.

At the same time, your telescope can pick up Comet 41P/Tuttle-Giacobini-Kresak which will be brightening between the stars of Leo and Cancer. 41P will continue to brighten over the next few months and should reach sixth magnitude in April making it possible for a sharp-eyed observer in a dark sky to pick it out without optical aid. Observers should always be on the lookout though, because comets can brighten unexpectedly at any time. Astronomers are not quite sure how comets produce these unpredictable outbursts which can cause the comet to brighten by a magnitude or more.

The third comet, 46P Wirtanen, wont come onto the scene until October 2018, but it will be worth waiting for as it will quickly brighten to fourth magnitude, well within naked eye visibility.

The Tucson based Planetary Science Institute is spearheading an international campaign to study the comas of these three comets. Amateur astronomers are invited to participate in the observing campaign called the 4*P Coma Morphology Campaign. See http://www.psi.edu/41P45P46P for details. By collecting images from multiple sources, astronomers hope to learn about the shape and rotational characteristics of the comets nuclei as well as how the comas evolve and change over time. The coma is the envelope of gas and dust that surrounds the nucleus of a comet. Visual observers who want to contribute observations of these comets should look into the PACA Project.

Visitors to the Patterson Observatory on Jan. 5 were able to view comet 45P through the 20-inch telescope. At the March 2 public night, comet 41P may be just visible in the large scope. Astronomers from the Huachuca Astronomy Club are always available at public night and they can help you plan your own observations of these comets. Patterson is located on the campus of the University of Arizona Sierra Vista. Public nights are free and the doors open just after sunset.

The morning sky all this month is adorned by Mercury low in the southeast and Saturn in the south-southeast. The evening sky is home to Venus and Mars in the west. Jupiter is a target for the overnight and will drift from the southeast to the southwest over the month. Jupiter will be in retrograde motion. Mark its position against the bright star Spica to trace its westward motion week to week over the next few months. Retrograde motion of a planet is caused by the earth overtaking it in its orbit. The planet appears to move backward in our sky as Earth races ahead of it.

The dwarf planet Ceres will be well placed among the stars of Cetus for viewing this month. For much of the 19th century, Ceres enjoyed status as a full-fledged planet, and was eventually demoted in similar fashion to Pluto. The largest object in the asteroid belt, Ceres was considered an asteroid until it was again elevated to dwarf planet by the same IAU convention that changed Plutos designation. This is a good time to see it, although you will need a telescope and a good map to find it. You can download freeware planetarium programs like Stellarium, Carte du Ceil, or Sky Map to pinpoint exactly where to look to catch this tiny world.

Read this article:

A comet tale - Sierra Vista Herald