Catch Comet 21/P Giacobini-Zinner at Its Best

Comet 21/P Giacobini-Zinner from August 14th. Image credit and copyright: Rolando Ligustri.

A periodic comet may put on a fine show for northern hemisphere viewers over the next few months.

Comet 21/P Giacobini-Zinner is currently a fine binocular comet, shining at +8th magnitude as it cruises across the constellation Cassiopeia. This places it above the horizon for the entire night for observers north of the equator in August, transiting the local meridian at dawn. And unlike most comets that get lost in the Sun’s glare (like the current situation with C/2017 S3 PanSTARRS), we’ll be able to track Comet 21/P Giacobini-Zinner right through perihelion on September 10th.

The orbit of comet 21P, showing the comet’s position at closest approach. Credit: NASA-JPL.

This is because the comet is on a short period, 6.6 year orbit around the Sun that takes it from an aphelion of 6 Astronomical Units (AU) exterior to Jupiter’s orbit, to a perihelion of 1.038 AU, just 3.3 million miles (5.2 million kilometers) exterior to Earth’s orbit. The 2018 apparition sees the comet pass 0.392 AU (36.5 million miles/58.3 million kilometers) from the Earth on September 11th.

This is the closest passage of the comet near Earth since September 14th, 1946, and won’t be topped until the perihelion passage of September 18th, 2058. Its next cycle of passes to Earth closer than 0.1 AU aren’t until next century in the years 2119 and 2195, respectively.

Comet 21/P from August 10th. Image credit and copyright: John Purvis.

Discovered by astronomer Michel Giacobini at the Côte d’Azur Observatory in Nice, France on the night of December 20th, 1900 as it was crossing the constellation Aquarius, the 21st periodic comet was recovered two orbits later by Ernest Zinner on October 23rd, 1913 as it passed a series of variable stars near Beta Scuti.

Though the comet generally tops out at +8th magnitude, it has been known to undergo periodic outbursts near perihelion, bringing it up about 3 magnitudes (about 16 times) in brightness. This occurred most notably in 1946.

The light curve for Comet 21/P. The black dots represent actual observations and magnitude observations. Credit: Seiichi Yoshida’s Weekly Information on Bright Comets.

Comet 21/P Giacobini-Zinner is also the source of the Draconid (sometimes referred to as the Giacobinid) meteors, radiating from the constellation Draco the Dragon on and around October 7th and 8th. Feeble on most years, this shower can produce surprises, such as occurred in 1998, 2005 and most recently in 2011, when a Draconid outburst topped a zenithal hourly rate of 400 meteors per hour, flirting with ‘meteor storm’ status. And while we’re not expecting a meteor storm to accompany the 2018 perihelion passage of Comet 21/P Giacobini-Zinner, you just never know… it’s always worth keeping an eye out on early October mornings for the “Tears of the Dragon,” just in case. Note that the Moon reaches New phase on October 9th, just a few days after the meteor shower’s expected annual peak, a fine time to watch for any unheralded Draconid outbursts.

Prospects for Comet 21P

The comet is visible from the northern hemisphere through the remainder of August and all through September as it glides across Auriga, Taurus and Gemini and visits several well known celestial sights. In fact, it actually transits in front of several deep sky objects, including Messier 37 (Sept 10th), and Messier 35 (Sept 15th).

Comet 21P passes in front of open cluster Messier 35 on September 15th. Credit: Starry Night.

The comet will be moving at about two degrees per day when it’s nearest to the Earth, on and around September 11th.

We begin to lose the comet, as it heads southward in late October. Still, the comet is over 50 degrees above the eastern horizon at dawn come October 1st as seen from latitude 30 degrees north, having maintained a similar elevation throughout most of September. Not bad at all.

Here are some upcoming dates with destiny for Comet 21/P Giacobini-Zinner:

August 19: Crosses into the constellation Camelopardalis.

August 29: Crosses into the constellation Perseus.

August 30th: Crosses into the constellation Auriga.

The celestial path of Comet 21P from August 16th through September 15th. Credit: Starry Night.

September 2: Passes one degree from the bright star Capella.

Sept 7-8: Grouped 2 degrees from the open clusters M36 and M38.

Sept 10: Photo-Op: Skirts very near the open cluster M37. Also reaches perihelion on this date, at magnitude +7.

Sept 11: Passes closest to the Earth, at 0.392 AU distant.

Sept 13: Nicks the corner of the constellation Taurus.

Sept 14th : Enters the constellation Gemini.

Sept 15th: Photo-Op: crosses in front of the open cluster M35.

Sept 16: Crosses the ecliptic southward and near the +3.3 magnitude star Propus (Eta Geminorum).

Sept 17: Crosses into Orion.

Sept 21: Crosses into Gemini.

Sept 23: Crosses into Monoceros.

Sept 24: Passes near the Christmas Tree Cluster, NGC 2264.

The celestial path of Comet 21P from September 15th through October 15th. Image credit: Starry Night.

Oct 1: Crosses the galactic plane and the celestial equator southward.

Oct 7: Crosses in front of the open cluster M50.

Oct 10: Crosses into Canis Major.

Oct 31st: Passes near the bright star Aludra and may drop below +10th magnitude.

Binoculars are your best friend when you’re looking for comets brighter than +10th magnitude. With a generous field of view, binoculars allow you to sweep a suspect area until the faint fuzzball of a comet snaps into view. I like to ‘ambush’ a comet as it passes near a bright star, and a good time to spot comet 21/P Giacobini-Zinner is coming right up on September 2nd when it passes less than one degree from the bright +0.1 magnitude star Capella.

Don’t miss this year’s fine apparition of Comet 21/P Giacobini-Zinner, coming to a night sky near you.

Preview: Comet 45P/Honda–Mrkos–Pajdušáková Brightens in December

Looking for a good binocular comet? Well, if luck is on our side, we should be getting our first looks at periodic Comet 45P/Honda-Mrkos-Pajdušáková as it tops +10th magnitude in dusk skies over the next few weeks. 

Image credit: Starry Night.
The swift path of Comet 45P/Honda-Mrkos-Pajdušáková on the nights of February 9th to February 12th. Image credit: Starry Night.

Comet 45P/Honda-Mrkos-Pajdušáková is expected to reach maximum brightness around late February 2017. Discovered independently by astronomers Minoru Honda, Antonin Mrkos and L’udmila Pajdušáková on December 3rd, 1948, Comet 45P/Honda-Mrkos-Pajdušáková orbits the Sun once every 5.25 years on a short period orbit. Comet 45P/Honda-Mrkos-Pajdušáková is set to break binocular +10th magnitude brightness in mid-December 2017, and may reach a maximum brightness of magnitude +7 from January through February 2017.

Slovak astronomer ?udmila Pajdušáková
Slovak astronomer ?udmila Pajdušáková, co-discoverer of 5 comets, including Comet 45P/Honda-Mrkos-Pajdušáková. Image credit: The Skalnaté Pleso Observatory.

Currently and through the end of 2016, the comet sits towards the center of the Milky Way Galaxy in Sagittarius at a faint +15th magnitude in the evening sky. The comet may break +10th magnitude and become very briefly visible in the first few weeks of December before getting too close to the Sun to observe in late 2016 and crossing into the morning sky in early 2017.

The path of Comet 45/P from mid-November through December 15th, 2016. Image credit: Starry Night.
The path of Comet 45/P from mid-November through December 15th, 2016. Image credit: Starry Night.

Visibility prospects: At its brightest, Comet 45P/Honda-Mrkos-Pajdušáková will be passing through the constellation Hercules during closest approach on February 11th. The comet then passes through the constellations of Corona Borealis, Boötes, Canes Venatici, Ursa Major into Leo through to the end of February as it recedes. In the second week of February, the comet is visible in the dawn sky 82 degrees west of the Sun at maximum brightness. This apparition favors the northern hemisphere. The comet will reach perihelion on December 29th, 2016 at 0.53 Astronomical Units (AU) from the Sun, and the comet passes just 0.08 AU (7.4 million miles) from the Earth on February 11th at 14:44 UT. The comet made a slightly closer pass in 2011, and was a fine binocular object that time around. At its closest, the comet will cross nine degrees of sky from one night to the next. Some notable dates for comet 45P/Honda-Mrkos-Pajdušáková are:

November 23rd: Venus passes 6′ from the comet.

December 12th: May break 10th magnitude.

December 14th: Passes near M75.

December 15th: Crosses into the constellation Capricornus.

January 4th: Passes near the +4th magnitude star Theta Capricorni

January 10th: Crosses the ecliptic northward.

January 16th: Passes into Aquarius.

January 22nd: Passes near NGC 7009, M72 and M73.

January 25th: Passes 8 degrees from the Sun and into the dawn sky.

January 28th: Crosses into Aquila.

February 3rd: Crosses the celestial equator northward.

February 4th: Passes 4′ from the star +3.3 magnitude star Delta Aquilae.

February 6th: Crosses the Galactic equator.

February 7th: Crosses into Ophiuchus.

February 9th: Crosses into Hercules.

February 16th: makes a wide pass near M3.

February 19th: Drops back below +10th magnitude.

Image credit: NASA/JPL.
The path of Comet 45P/Honda-Mrkos-Pajdušáková through the inner solar system. Image credit: NASA/JPL.

This is the final close (less than 0.1 AU) passage of Comet 45P/Honda-Mrkos-Pajdušáková near the Earth for this century.

On July 1st 1770, Comet D/1770 L1 Lexell passed 0.0151AU from the Earth; a comet in 1491 may have passed closer. Next year’s passage of 45P/Honda-Mrkos-Pajdušáková ranks as the 21st closest passage of a comet near the Earth.

The light curve of Comet 45/P
The light curve of Comet 45/P Honda-Mrkos-Pajdušáková. Credit: Seiichi Yoshida’s Weekly Information About Bright Comets.

Why do comets end up with such cumbersome names? Well, comets derive their names from the first three discovers that submit the find within a 24 hour period to the Minor Planet Center’s Central Bereau for Astronomical Telegrams, which, in fact, received its last ‘telegram’ during the discovery of Comet Hale-Bopp around two decades ago. Increasingly, comets are receiving names of all sky surveys such as LINEAR and PanSTARRS from robotic competition against amateur hunters. It does seem like you need an umlaut or the chemical symbol for boron to in your moniker to qualify these days… rare is the ‘Comet Smith.’ But hey, it’s still fun to watch science journalists try and spell the Icelandic volcano Eyjafjallajökull and comet Churyumov-Gerasimenko over and over… Perhaps, we should insist that our first comet discovery is actually spelled Comet Dîckînsðn…

And Comet 45/P is just one of the fine binocular comets on deck for 2017. We’re also expecting Comet 41P/Tuttle-Giacobini-Kresák, 2/P Encke, C/2015 ER61 PanSTARRS Comet C/2015 V2 Johnson to break +10th magnitude next year… and the next great naked eye ‘Comet of the Century’ could light up the skies at any time.

Goldstone radar pings comet 45/P back in 2011. Image credit: NASA.
Goldstone radar pings comet 45/P back in 2011. Image credit: NASA.

Binoculars are the best tool to observe bright comets, as they allow you to simply sweep the star field and admire the full beauty of a comet, coma, tail(s) and all. Keep in mind, a comet will often appear visually fainter than its quoted brightness… this is because, like nebulae, that intrinsic magnitude is ‘smeared out’ over an extended area. To my eye, a binocular comet often looks like a fuzzy, unresolved globular cluster that stubbornly refuses to snap into focus.

Don’t miss your first looks at Comet 45/P 45P/Honda-Mrkos-Pajdušáková, as it spans 2016 into 2017.