Watch for comet C/2020 F3 NEOWISE at dusk in late July… if it survives perihelion.
Update – Friday July 3rd: Comet C/2020 F3 NEOWISE reaches perihelion today at 16:18 UT/12:18 PM EDT. As of writing this, several observers worldwide have recovered the comet at dawn, and it seems to be holding steady at magnitude +0.5. The dawn apparition is, however, a tough catch, as the comet stays very low to the northeast at dawn in early July. We’ve added in a finder chart (below) for this brief dawn apparition; things improve greatly towards mid-July, as the comet shifts over to the dusk sky and heads out away from the Sun. Let’s hope it stays bright, and maybe throws an outburst our way! We’ll continue to post updates on Twitter as @Astroguyz as the celestial situation warrants.
Ready for one more? 2020 has thus far offered up a steady celestial parade of binocular comets, including C/2019 Y1 and Y4 ATLAS, 2017 T2 PanSTARRS, and 2019 U6 Lemmon. Now, we have one more inner solar system interloper from the Oort Cloud with potential: C/2020 F3 NEOWISE.
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The comet was discovered by the NEOWISE space telescope on March 27, 2020. The NEOWISE mission transitioned from its primary Wide-field Infrared Survey Explorer (WISE) mission in September 2013, adding NEO (as it started a dedicated hunt for Near Earth Objects) to its moniker. To date, NEOWISE has discovered 15 comets during this extended phase.
The comet is on a retrograde orbit, inclined 129 degrees relative to the ecliptic plane. Its orbit is 4,300 years inbound, altered to a 6,500 year outbound path (thanks to the solar system goal-tending efforts of Jupiter). The comet will then head for an aphelion 754 AU (Astronomical Units) from the Sun, about 200 AU interior to the aphelion of distant 90377 Sedna.
The Prospects for F3 NEOWISE
The comet brightened dramatically as it transited through the field of view of the joint NASA/ESA Solar and Heliospheric Observatory’s (SOHO) LASCO C3 camera in late June, reaching magnitude +0.5 as of June 30th. The LASCO passage occurred from June 23 to June 28th, reaching an apparent 7 degrees from the disk of the Sun on June 27th. This comes as SOHO celebrates its 4,000th comet discovery.
All eyes will be on the comet in early July, as it approaches perihelion interior to the orbit of Mercury on July 3rd, 0.29 AU (26.97 million miles/43.4 million kilometers) from the Sun. This is the key time for any comet, when heating, solar wind and gravity is at its maximum force… if a comet is dynamically new or loosely cobbled together, this is generally right around the time it will fall apart. This famously happened to Comet C/2012 S1 ISON on U.S. Thanksgiving Day 2013. A happier tale was just a few years prior, When Comet W3 Lovejoy survived a blazing 2011 perihelion passage just 87,000 miles (!) from the surface of Sun, about a third of the distance from the Earth to the Moon. Comet F3 NEOWISE just crossed the ecliptic plane northward in late June, setting the stage for its July apparition in the northern sky.
Comet C/2020 F3 NEOWISE will make a very brief dawn apparition in July the week after perihelion, hugging the horizon under 5 degrees elevation to the northeast as a tough catch, 30 minutes prior to sunrise.
‘If’ comet C/2020 F3 NEOWISE holds together through perihelion in early July, and ‘if’ it stays dynamically bright and active (always two big ‘ifs’ when it comes to comets), we should have a nice binocular (possibly naked eye) comet at dusk for northern hemisphere observers in mid-July. The comet will attain greater than 10 degrees elevation above the western horizon 45 minutes after sunset for mid-northern latitudes come mid-July, vaulting up through the constellation Lynx into Ursa Major near the ‘Three Leaps of the Gazelle’.
One can hope this one puts on a decent show. Here’s the month-by-month breakdown of celestial dates with destiny for comet F3 NEOWISE. As always, passes near notable celestial objects are less than one degree, unless otherwise noted:
1-Crosses the ecliptic plane northward.
2-Crosses into Auriga.
3-Reaches perihelion 0.29 AU from the Sun.
13-Crosses into the constellation Lynx.
18-Crosses into Ursa Major
19-Passes near +3 magnitude star Talitha (Iota Ursae Majoris) and the +3.6 magnitude star Al Kapra.
21- Reaches its most northward point, at ~47 degrees north.
23-Closest to the Earth, at 0.692 AU distant moving 4 degrees a day.
24-Passes near the +4.7 magnitude star Omega Ursae Majoris.
30-Passes into the constellation Coma Berenices.
31-Passes near +4.3 Gamma Comae Berenices.
1-May drop back down below naked eye visibility.
1-Passes near the +10th magnitude galaxy NGC 4565.
3-Passes near the +9th magnitude Black Eye galaxy (Messier 64).
6-Passes near the +8.5 magnitude globular cluster M53, and the +4.3 magnitude star Diadem (Alpha Comae Berenices) .
10-Nicks the corner of the constellation Virgo.
13-Nicks the corner of the constellation Boötes.
16-Crosses back into the constellation of Virgo.
26-Crosses the celestial equator southward.
1- May drop back down below +10th magnitude.
Observing comets brighter than +10th magnitude is as simple as sweeping the suspect field with binoculars and looking for a fuzzy ‘star’ that stubbornly refuses to snap into focus. Like globulars and other deep sky objects, comets can often appear visually fainter than the quoted magnitude, owing to the fact that all that brightness is ‘smeared out’ over an apparent surface area. Missions to comets such as the European Space Agency’s Rosetta mission to comet 67P/Churyumov-Gerasimenko demonstrated just how dark these objects are up close. Likewise, imaging comets is similar to photographing deep-sky objects, requiring stacking of multiple exposures. Be sure to track the comet against the starry background whilst exposing frames, as a fast-mover such as F3 NEOWISE can move noticeably even after only an hours’ worth of observation.
We may still be waiting for the next magnificent naked eye comet of the 21st century, but in the meantime, the steady stream of binocular comets lead by F3 NEOWISE will keep us entertained through the summer of 2020.
Lead image credit: Comet F3 NEOWISE from May 20th, taken from Farm Tivoli in Namibia. Image Credit and Copyright: Gerald Rhemann.