See Comet C/2015 ER61 PanSTARRS at its Best

ER61 PanSTARRS
ER61 PanSTARRS
Comet C/2015 ER61 PanSTARRS shortly after outburst on April 8th. Image credit and copyright: John Purvis.

Have you been following the springtime parade of bright comets? Thus far, the Oort cloud has offered up several fine binocular comets, including Comet 2/P Encke, 41/P Tuttle-Giacobini-Kresak, 45/P Honda-Mrkos-Pajdusakova, C/2016 U1 NEOWISE and C/2017 E4 Lovejoy. Now, another comet joins the dawn ranks, as it brightens up ahead of expectations: 2015 ER61 PanSTARRS.

Discovered on March 15th, 2015 by the prolific PanSTARRS-1 NEO survey atop Haleakala in Maui, Hawaii, Comet ER61 PanSTARRS made our who’s-who list of bright comets to watch for in 2017. The odd “ER61” designation stems from the early identification of the object as an asteroid, before it presented observers with a cometary appearance.

ER61 PanSTARRS Skychart
The path of Comet C/2015 ER61 PanSTARRS through the sky from early May through mid-August. Credit: Starry Night Education software.

Late northern hemisphere Spring through Summer sees the comet maintaining a decent elevation above the eastern horizon at dawn, gliding north and parallel to the ecliptic plane through the constellations Pisces, Aries and Taurus from May through mid-August. The comet passed 1.08 AU from the Earth last month on April 4th, and is now racing away from us. The comet’s location near the March equinoctial point on the celestial hemisphere assures an equally good apparition for both the northern and southern hemisphere. As seen from latitude 30 degrees north, the comet sits 30 degrees above the eastern horizon, through the remainder of May. Venus also makes a brilliant beacon to track down Comet ER61 PanSTARRS, as the planet heads towards greatest elongation 46 degrees west of the Sun on June 3rd.

The orbit of Comet ER61 PanSTARRS through the inner solar system. Credit: NASA/JPL.

The comet is also on a 7,591 year long orbit inbound, which takes it out nearly 2,500 AU from the Sun. That’s 190 times the Pluto-Sun distance, and the fourth most distant aphelion of any solar system object known. The 2015-2017 passage of the comet through the inner solar system actually shortened the orbit of Comet ER61 PanSTARRS down to an aphelion of ‘only’ 854 AU due to a 0.9 AU pass near Jupiter last year on March 28th, 2016. A similar orbital shortening by Jove occurred for Comet Hale-Bopp in 1996, which came in on an 4,200 year orbit and departed the inner solar system on a shorter 2,500 year path around the Sun.

The projected light curve for Comet C/2015 ER51 PanSTARRS. The purple line denotes perihelion, and the black dots are actual observations. Adapted from Seiichii Yoshida’s Weekly Information for Bright Comets.

Prospects and Prognostications

Observers reported an outburst from the comet last month in the first week of April, causing it to jump about 2 magnitudes in brightness. Right now, it’s holding steady at +7th magnitude. Unfortunately, the Moon reaches Full phase this week on May 10th, though you’ve still got a slim window to hunt for the comet after Moonset and before sunrise. Once the Moon moves towards a slender crescent phase next late week, we’ll once again have dark predawn skies ideal for comet hunting.

Here are some key dates for Comet C/2015 ER61 PanSTARRS as it glides through the dawn sky:

(Stars highlighted are brighter than +5th magnitude, and passes are less than a degree unless otherwise noted.)

May 10th: Reaches perihelion at 1.04 astronomical units (AU) from the Sun.

May 12th: Passes near the +4.9 magnitude star 19X Piscium.

May 20-23rd: Passes less than 10 degrees from Venus.

May 21st: The waning crescent Moon passes less than 10 degrees to the south.

June 10th: Passes near the +3.6 magnitude star Eta Piscium.

June 11th: Passes near the galaxy M74.

June 16th: Passes into the constellation Aries.

June 19th: The waning crescent Moon passes 9 degrees to the south.

July 13th: Passes near (less than 5′) the +4.6 magnitude star Epsilon Arietis.

July 18th: The waning crescent Moon passes 9 degrees to the south.

July 23rd: Passes near the +4.8 star Zeta Arietis.

The comet versus Venus in the dawn sky – looking eastward on May 15th. Credit: Stellarium.

August 2nd: Crosses into the constellation Taurus.

August 15th: The waning crescent Moon passes 8 degrees to the south.

August 16th: Passes near M45 (The Pleiades)

After mid-August, Comet 2015 ER61 PanSTARRS will drop back down below +10th magnitude, not to return for several millennia to come.

Observing a comet like ER61 PanSTARRS is as simple as knowing where and when to look, then starting to slowly sweep the suspect area with binoculars for a little fuzzball looking like a globular cluster stubbornly refusing to snap into focus. In pre-telescopic times, ER61 PanSTARRS would’ve entered and exited the inner solar system unrecorded.

April ER61 PanSTARRS
Comet C/2015 ER61 PanSTARRS from April 12th. Image credit and copyright: Joseph Brimacombe.

Next up: We’ve got one more predicted comet on tap for 2017, as C/2015 V2 Johnson brightens up to +7th magnitude in mid-June. Keep watching the skies, as the next great comet of the century could always appear unannounced at any time.

Asteroid-Turned-Comet 2013 UQ4 Catalina Brightens: How to See it This Summer

Though ISON may have fizzled in early 2014, we’ve certainly had a bevy of binocular comets to track this year. Thus far in 2014, we’ve had comets R1 Lovejoy, K1 PanSTARRS, and E2 Jacques reach binocular visibility. Now, and asteroid-turned-comet is set to put on a fine show this summer for northern hemisphere observers.

Veteran stargazer and Universe Today contributor Bob King told the tale last month of how the asteroid formerly known as 2013 UQ4 became comet 2013 UQ4 Catalina. Discovered last year on October 23rd 2013 during the routine Catalina Sky Survey searching for Near Earth Objects based outside of Tucson Arizona, this object was of little interest until early this year.

Credit:
A recent image of 2013 UQ4 Catalina from June 16th. The development of fine tail structure can be seen. Credit: A. Maury & J.G. Bosch.

As it rounded the Sun, astronomers recovered the asteroid and discovered that it had begun to sprout a fuzzy coma, a very un-asteroid-like thing to do. Then, on May 7th, Taras Prystavski and Artyom Novichonok — of Comet ISON fame — conducted observations of 2013 UQ4 and concluded that it was indeed an active comet.

credit
The orbital path of UQ4 Catalina in early July. Created using the JPL Solar System Dynamics Small Body Database Browser.

Hovering around +13th magnitude last month, newly rechristened 2013 UQ4 Catalina was a southern hemisphere object visible only from larger backyard telescopes. That should change, however, in the coming weeks if activity from this comet holds up.

Light curve
The light curve of UQ4 Catalina with current observations (dots) noted. Credit:  Seiichi Yoshida/Aerith.net.

2013 UQ4 belongs to a class of objects known as damocloids. These asteroids are named after the prototype for the class 5335 Damocles and are characterized as long-period bodies in retrograde and highly eccentric orbits. These are thought to be inactive varieties of comet nuclei, and other asteroids in the damocloid series such as C/2001 OG 108 (LONEOS) and C/2002 VQ94 (LINEAR) also turned out to be comets. Damocloids also exhibit the same orbital characteristics of that most famous inner solar system visitor of them all; Halley’s Comet.

The path of Comet 9PM 30deg north
The path of Comet UQ4 Catalina looking towards the NE at 9PM local in early July from latitude 30 degrees north. Credit: Stellarium.

The good news is, 2013 UQ4 Catalina is brightening on schedule and should be a binocular object greater than +10th magnitude by the end of June. Recent observations, including those made by Alan Hale (of comet Hale-Bopp fame) place the comet at magnitude +11.9 with a bullet. The comet is currently placed high in the east in the constellation Pisces at dawn, and will soon speed northward and vault across the sky as it crosses the ecliptic plane this week. In fact, comet 2013 UQ4 Catalina reaches perihelion on July 6th only four days before its closest approach to the Earth at 47 million kilometres distant, when it may well reach a peak magnitude of +7. At that point, the comet will have an apparent motion of about 7 degrees a day — that’s the span of a Full Moon once every 1 hour and 42 minutes — as it rises in the constellation Cepheus to the northeast at dusk in early July. A fine placement, indeed. And speaking of the Moon, our natural satellite reaches New phase later this month on June 27th, another good reason to begin searching for 2013 UQ4 Catalina now.

Here’s a list of notable events to watch out for and aid you in your quest as comet 2013 UQ4 Catalina crosses the summer sky:

June 16th: The comet crosses north of the ecliptic plane.

June 20th: The waning crescent Moon passes 3 degrees from the comet.

starry nite
The celestial path of the comet from June 16th to July 15th… Credit: Starry Night Education software.

June 29th: Crosses into the constellation of Andromeda.

July 1st: Passes less than one degree from the +2nd magnitude star Alpheratz.

July 2nd: Crosses briefly into the constellation Pegasus before passing back into Andromeda.

July 6th: The comet reaches perihelion or its closest point to the Sun at 1.081 A.U.s distant.

July 7th: Crosses into the constellation of Lacerta and passes the deep sky objects NGCs 7296, 7245, 7226.

July 8th: Crosses into the constellation Cepheus and across the galactic plane.

July 9th: Passes a degree from the Elephant Trunk open star cluster.

July 10th: Passes less than one degree from the stars Eta (magnitude +3.4) and Theta (magnitude +4.2) Cephei.

July 10th: Passes 2 degrees from the +7.8 magnitude Open Cluster NGC 6939.

July 10th: Passes closest to Earth at 0.309 A.U.s or 47 million kilometres distant.

July 11th: Crosses into the constellation Draco.

July 11th: Reaches its most northerly declination of 64 degrees.

July 12th: Photo op: the comet passes 3 degrees from the Cat’s Eye Nebula.

July 15th- August 20th
… and the path of the comet from July 15th to August 20th. Credit: Starry Night.

July 17th: The comet passes into the astronomical constellation of Boötes.

July 31st: Passes just 2 degrees from globular cluster NGC5466 (+9th magnitude) and 6 degrees from the famous globular cluster Messier 3.

From there on out, the comet drops below naked eye visibility and heads back out in its 470 year orbit around the Sun. Be sure to check out comet 2013 UQ4 Catalina this summer… what will the Earth be like next time it passes by in 2484 A.D.?