A little periodic comet is visiting the inner solar system over the next few months. Comet 45/P Honda–Mrkos–Pajdušáková, a tiny piece of ice and dust left over from the earliest days of the solar system, moves periodically around the Sun every 5.25 years. It made its closest approach to the Sun on December 31, 2016 and it’s visible now. As it passes close to Earth in February, it will brighten and appear to move quickly across the sky from day to day. You’ll need binoculars to see it, but it’s worth following this little leftover hunk of the early solar system.
The last closest approach to the Sun of Comet 45/P came on September 28, 2011. During this apparition, the comet came within 0.06 AU (5.58 million miles) of Earth on August 15, 2011. That’s fairly close in cosmic terms and just 22x the Earth-Moon distance. The precise size of the Comet 45/P’s nucleus is uncertain, but it’s likely about 0.5 km to 1.6 km across. The famous Comet 1/P Halley, by contrast, has a nucleus ten times as wide.
During its latest visit, Comet 45/P reached perihelion (its closest approach to the Sun) on December 31, 2016. On February 11, 2017, will come within 0.08 AU (7.47 million miles) of Earth, a close approach but still far enough to pose no risk of impact. Astronomers estimate the comet’s brightness will peak just a little fainter than 6th magnitude in January and through February 2017 before beginning to fade. From December through January, the comet will swing through the constellation Capricorn, disappear into the sunset, then pick up speed when it reappears and move northwestward into Aquila, Hercules, Corona Borealis, Bootes, and Coma Berenices during February. As it speeds away from Earth in March and April, the comet moves into the constellation Leo.
The first map below, courtesy of Sky and Telescope magazine, shows the position of Comet 45/P through mid-January when it’s visible in the constellation Capricorn in the western sky after sunset. For the rest of January, the comet is lost in the Sun’s glare, but it reappears in the early morning sky from mid-February through mid-March (see second map). Astronomers expect the comet to reach peak brightness in early-to-mid February. It will not likely become bright enough to see with the unaided eye, but it will be easily visible in binoculars. In images, the comet is already showing a short, straight ion tail.
Comet 45/P was discovered by the Japanese astronomer Minoru Honda in December 1948, and nearly simultaneous observations were made by the Czech astronomer Antonin Mrkos and Slovak astronomer Ludmila Pajdušáková.
Honda himself was an interesting character and a legend in post-war Japan. From the late 1920s until the late 1930s, after a modest education, he worked with his parents on a farm. In his scant spare time he took to exploring the heavens with a tiny 28 mm telescope. His stargazing acumen eventually earned him a position at a professional Japanese observatory. Honda had learned that no Japanese astronomer had ever discovered a comet, so he set to work to become the first, and he systematically scanned the skies with a 15 cm reflector. He discovered his first comet in 1940, but he was shipped off to join the Japanese army during World War II. He picked up comet hunting after the war and discovered, in time, a total of 12 comets, his last three in the single year of 1968.
Honda’s work, especially in the grim years after the war, was an inspiration to a generation of young Japanese stargazers and amateur astronomers. In the early 1960s, a young astronomer and comet hunter named Kaoru Ikeya wrote to Honda for advice about how to find comets. Honda wrote back to Ikeya, cryptically:
“To observe the skies solely to seek a new comet is a hopeless task which demands a great deal of time and hard labor. But to observe the brilliant heavens for their own sake without thought of a discovery may bring good luck to your comet seeking.”
His advice worked. Ikeya discovered his first comet in early 1964, and in 1965, along with another Honda acolyte, Tsutomu Seki, discovered Comet 1965 S1 (Ikeya-Seki), a brilliant sungrazing comet which became one of the greatest comets of the 20th century.
Comet 45/P Honda–Mrkos–Pajdušáková will not become a so-called “Great Comet”. It will not even become bright enough to see with the naked eye. But it presents a fine opportunity for you to practice your observing skills, witness the mechanics of the solar system in action, and prepare for the overdue yet unpredictable arrival of another bright comet, hopefully one day soon.