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.

Catch Comet C/2017 S3 PanSTARRS in Outburst

Comet S3 PanSTARRS
Comet S3 PanSTARRS
Comet C/2017 S3 PanSTARRS from July 22nd. Image credit and copyright: hodorgabor

Comets are one of those great question marks in observational astronomy. Though we can plot their orbits thanks to Newton and Kepler, just how bright they’ll be and whether or not they will fizzle or fade is always a big unknown, especially if they’re a dynamic newcomer from the Oort Cloud just visiting the inner solar system for the first time.

We had just such a surprise from a cosmic visitor over the past few weeks, as comet C/2017 S3 PanSTARRS erupted twice, brightening into binocular visibility. Discovered on December 23rd 2017 during the PanSTARRS survey based on Haleakala, Hawai’i, S3 PanSTARRS is on a long-period, hyperbolic orbit and is most likely a first time visitor to the inner solar system.

The orbital path of comet S3 PanSTARRS through the inner solar system. Credit NASA/JPL.

S3 PanSTARRS was not only rocked by two new outbursts in quick succession, but seems to have undergone a tail disconnection event just last week, leveling off its brightness at around +8 magnitude and holding. This puts it in the range of binoculars under dark skies, looking like a fuzzy globular that refuses to snap into focus as it currently glides through the constellation of Camelopardalis the Giraffe the dawn sky.

The path of comet S3 PanSTARRS through August. Credit: Starry Night.

As July closes out, the time to catch sight of Comet S3 PanSTARRS is now, before it’s lost in the Sun’s glare. From latitude 40 degrees north, the comet sits 20 degrees above the northeastern horizon, about an hour before sunrise. By August 7th however, it drops below 10 degrees altitude. From there, the comet begins to circle the Sun as seen from the Earth beginning to favor southern hemisphere observers at dawn, who may be able to track it straight through perihelion on August 16th, if its brightness holds up. From there, northern hemisphere viewers may get a second view at dawn in September, again, if its brightness holds.

The dawn path of the comet looking northeast at dawn from latitude 35 degrees north, from July 31st through the first week of August. Credit: Starry Night.

You never know when it comes to comets. Here’s a brief rundown of the celestial happenings for comet C/2017 S3 PanSTARRS:

August

3- Crosses into the constellation Gemini.

4- Passes near the bright star Castor.

5- Passes near the bright star Pollux.

7- Crosses into the constellation Cancer.

7- Passes closest to the Earth, at 0.758 Astronomical Units (AU) distant.

8- Crosses southward over the ecliptic plane.

9- Passes just 4 degrees from the Beehive cluster, M44.

11- Passes 2 degrees from the open cluster M67.

12- Passes 10.5 degrees from Sun (1st apparent close pass as seen from the Earth)

13- Crosses into the constellation Hydra.

15- Reaches maximum brightness: the comet may top +2nd magnitude in mid-August.

16- Reaches perihelion at 0.21 AU from the Sun.

18- Crosses into the constellation Sextans.

30-Crosses into the constellation Leo.

31-Crosses the ecliptic plane northward.

The projected light curve for comet S3 PanSTARRS. The black dots are actual observations. Credit Seiichi Yoshida.

September

3- passes 4 degrees from the Sun.

25- Crosses into the constellation Coma Berenices.

From there, Comet C/2017 S3 PanSTARRS drops back below 6th magnitude in September, then below 10th magnitude in October as it heads back off into the icy realms of the outer solar system.

Be sure to nab this icy interloper why you can. The quote comet hunter David Levy, “Comets are like cats… they have tails, and they do exactly what they want.”

Top 2018 Astronomy Events

2018 Astronomy – The final occultation of the bright star Aldebaran by the Moon for 2017. Dave Dickinson

Happy New Year 2018.

One of the toughest choices we made last year was to not write a full astronomy guide for 2018. We’ve done this in one iteration or another now for about a decade, but an ongoing project (also astronomical in nature) has consumed most of our writing hours… but we recently realized that we can still take stock in what’s in the sky for the year ahead, and give you a sneak peek at part of our project for the end of 2018.

The Rules:

What we’ve constructed is a simple three month strip chart denoting the top astronomical events by date. The big idea was to make a latitude independent version of the familiar hourglass chart, and distill the events down to the very best.

For the top events listed below for the entire year, we considered:

Meteor showers with a ZHR greater than 10, where the phase of the Moon is not within a week of Full;

-Oppositions of the outer planets;

-Elongations of the inner planets;

Eclipses of the Sun and Moon;

-The closest conjunction of two naked eye planets for 2018;

-The best easily visible occultation of a bright star and a planet for 2018;

Comets slated to reach perihelion in 2018 and forecast to break +10th magnitude.

The Best of 2018: (events in bold are the “best of the best”)

-Meteor Showers: Lyrids (April 22), Daytime Arietids (June 7), Perseids (Aug 12), Draconid Outburst? (Oct 8) Orionids (Oct 10), Andromedids (Dec 3), Geminids (Dec 14).

-Oppositions: Mars (Jul 27), Jupiter (May 8), Saturn (Jun 27), Uranus (Oct 23), Neptune (Sep 7), Pluto (Jul 12)

-Elongations: Mercury (Jan 1, Mar, 15, Apr 29, Jul 12, Aug 26, Nov 6, Dec 15). Venus (Aug 17)

-Eclipses: A Total Lunar eclipse for Asia, Australia the Pacific and western North America (Jan 31), a partial solar for the southern tip of South America (Feb 15), a partial solar for Tasmania and southernmost Australia (Jul 13), a total lunar for South America, Europe, Africa, Australia and Asia (Jul 27), and a partial solar for Scandinavia and northern Asia (Aug 11),

-Closest conjunctions: Mars-Jupiter (January 7)

-Best occultation (planet): Mars for the southern tip of South America (Nov 16). The Moon occults 4 planets in 2018: Mercury (2), Mars (1), Venus (1), and Saturn (1)

-Best occultation (star): Aldebaran for northern Asia and Europe (Feb 23) The Moon occults Aldebaran 9 times and Regulus 5 times in 2018.

-Periodic Comets over magnitude +10 with perihelion dates: C/2016 M1 PanSTARRS (Aug 10, +9), C/2016 R2 PanSTARRS (May 9, mag +9), C/2017 S3 PanSTARRS (Aug 16, +4), 21P/Giacobini-Zinner (Sep 10, mag +4), 38P/Stephan-Oterma (Nov 11, mag +9), 46P/Wirtanen (Dec 13, mag +3)

The astronomical strip chart for the first 3 months of 2018:

Astronomical events for Jan-Mar 2018 (click the chart to see the full-sized version).

What’s Up for January-March 2018:

-The month of January 2018 kicks off with a Full Moon on the night of January 1-2, the first of two Full Moons in the month, the second of which is sometimes referred to as a Blue Moon. March 2018 also contains two Full Moons (March 2 and March 31), while the 28 day month of February lacks a Full Moon, the only month that can do so.

The Moon also continues its cycle of occultations of the bright stars Regulus and Aldebaran, favoring the following locations;

January 5- Regulus (Northern North America)

January 27-Aldebaran (Northern Pacific)

February 1- Regulus (NE Asia)

February 23- Aldebaran (northern Europe/northern Asia)

March 1-Regulus (North Atlantic)

March 22-Aldebaran (North Atlantic)

March 28-Regulus (NE Asia/Alaska)

The Moon also occults Mercury for NW North America (in the daytime) on February 15th, then Venus just 22 hours later favoring the southern tip of South America (in the daytime), though both events are too close to the Sun to observe.

The first of two eclipse seasons for 2018 also begins in January, with a total lunar eclipse centered over the Pacific Ocean and surrounding regions on January 31st and a 60% partial solar eclipse for the southern tip of South America on February 15.

Venus reaches superior conjunction on January 9th, and moves into the dusk sky for a brilliant dusk apparition later in 2018. Mercury reaches greatest elongation 23 degrees west of the Sun in the dawn sky on January 2, then reaches superior conjunction on the farside of the Sun on February 17 before catching up with Venus and passing just 66′ from it on March 4.

Mars, Jupiter and Saturn remain dawn objects through the first quarter of 2018, with Mars passing just 12′ from Jupiter on January 12.

Let us know what you think, as this quarterly product is very much a work in progress… we plan on bringing you the quarterly astronomical graphic chart here on Universe Today every three months.

We’re looking forward to bringing you another great year of sky watching in 2018!

Here Comes Comet Heinze for the Holidays

Comet C/2017 T1 Heinze passes near the galaxy NGC 2706 on November 25th. Image credit and copyright: Charles Bell.

Yeah, we’re still all waiting for that next great “Comet of the Century” to make its presence known. In the meantime, we’ve had a steady stream of good binocular comets over the past year both expected and new, including Comet C/2017 O1 ASASSN1, 45/P Honda-Mrkos-Pajdušáková and Comet 41P Tuttle-Giacobini-Kresák (links). Now, another newcomer is set to bring 2017 in over the finish line.

The Discovery: Astronomer Aren Heinze discovered Comet C/2017 T1 Heinze as a tiny +18th magnitude fuzzball on the night of October 2nd, 2017. The comet will juuust breech our “is interesting, take a look” +10th magnitude cutoff in the final weeks of December leading into January, perhaps topping out around +8th magnitude.

Heinze discovered his first comet as part of the Asteroid Terrestrial-Impact Last Alert System (ATLAS) search program looking for hazardous objects using the eight 50 cm Wright-Schmidt telescope array atop Haleakala and Mauna Loa in the Hawaiian Islands.

The passage of Comet Heinze through the inner solar system. Credit: NASA/JPL

The orbit for Comet Heinze is an intriguing one, and as is often the case with comets, tempts us with what could have been. Heinze will vault over the ecliptic headed northward on Christmas Day, and reaches perihelion 87 million km (0.58 AU) from the Sun on February 21st, 2018. Closest passage from Earth for Comet Heinze is 33 million km (0.22 AU) on January 4th, 2018, when the comet will appear to move an amazing seven degrees a day through the constellation Camelopardalis.

But it’s the southward passage of Heinze though the ecliptic on April 1st that gives us pause, only 0.0144 AU exterior of Earth’s orbit… had this occurred on July 4th, we might’ve been in for a show, with the comet only 2.1 million kilometers away! Heinze seems like a tiny body as comets go, and there’s discussion that the comet is dynamically new and may end up shredding its nucleus all together. (link)

On a steep 97 degree inclined retrograde orbit, Comet Heinze also has a knife edge hyperbolic eccentricity of nearly 1.0. As with many long period comet, it’s tough to tell if Comet Heinze is a true denizen of our solar system, or just visiting. 2017 also saw the first asteroid whose extra-solar source was clear, as I/2017 U1 ‘Oumuamua, which passed through the inner solar system this past October.

The December path of Comet Heinze. Starry Night.

The Prospects: Currently, Comet Heinze is located highest to the south around 5AM local for northern hemisphere observers. Expect this situation to change to around 2 AM towards months end, as the comet is higher placed in the constellation Lynx come January 1st, 2018 as it nears opposition.

Comet observer Charles Bell noted on November 27th that Comet Heinze currently displays a short fan-shaped tail, about 88 days before perihelion.

Here’s the blow-by-blow for Comet Heinze for the next few months (passages mentioned here are to within a degree unless otherwise noted).

December

7- Crosses the celestial equator northward.

16- Passes near +3 magnitude star Zeta Hydrae.

18- Crosses into the constellation Cancer.

21- Passes near the open cluster M67.

25- Photo op: passes near the Beehive Cluster M44 and crosses the ecliptic northward.

29- Skirts the corner of the constellation Gemini and crosses into the Lynx.

The January 2018 passage of Comet Heinze through the inner solar system. Starry Night

January

1- May break +10th magnitude?

1- Passes near the +4.5 magnitude star 21 Lyncis.

2- Reaches opposition.

3- Passes near the +4.5 magnitude star 2 Lyncis and into the constellation Camelopardalis.

5- Passes near the +4 magnitude star Alpha Camelopardalis.

6- Passes 31 degrees from the north celestial pole.

7- Crosses into the constellation Cassiopeia.

10-Crosses the galactic equator southward.

13- Crosses into the constellation Andromeda.

14-Crosses into the constellation Lacerta.

17- Passes near the +4.5 magnitude star 6 Lacertae.

21- Passes near the +4 magnitude star 1 Lacertae.

23- Crosses into the constellation Pegasus.

February

26- Passes near the globular cluster M15.

March

1- May drop back down below +10th magnitude?

heinze
The projected light curve for Comet Heinze. Credit: Seiichi Yoshida’s Weekly Info on Bright Comets.

And though Comet Heinze won’t join their ranks, here’s a list of the great comets of the past century:

You could say we’re due.