Comet P1 Nishimura Could Be Bright Over the Next Few Weeks

New Comet P1 Nishimura graces the August dawn sky…but how bright will it get?

Hello. In a predictable clockwork Universe, a new comet is always the one wildcard that can over- or under-perform expectations. The most dramatic ones often crop up with scant warning: witness Comet IRAS-Araki-Alcock in 1983, and Comet B2 Hyakutake in 1996.

Now, we have a new comet that could reach naked eye visibility over the next few weeks: C/2023 P1 Nishimura. The comet was discovered by Hideo Nishimura while shooting wide-field images from Kakegawa, Japan on the night of August 11^th. At the time, the comet displayed respectable a 5’ coma. Score one for the human observers, versus robotic all-sky surveys…

Getting brighter… Comet C/2023 P1 Nishimura from August 15th, just before confirmation. Image credit and copyright: Dan Bartlett.

Currently at +9^th magnitude (with a bullet) in the constellation Gemini, the comet is now well-placed in the predawn sky. With binoculars, I could just make out the smudge of the comet this morning near Delta Geminorum. I was observing from Jimena de la Frontera in southern Spain.

The comet was initially listed as simply HN00003 on the IAU’s Minor Planet Center PCCP site, before receiving a formal name. P1 Nishimura is expected to brighten to +3 or +2 magnitude in early September, though it will also be near the Sun at that time. The comet passes 0.29 Astronomical Units (AU) or 43 million kilometers (26.7 million miles) from the Earth on September 13^th, and reaches perihelion 0.22 AU (33 million kilometers or 20.5 million miles) from the Sun interior to the orbit of Mercury on September 18^th.

An Intriguing Orbit

At its closest approach to Earth in mid-September, the comet will cross four degrees of sky per day.

The orbital path of Comet Nishimura. Credit: NASA/JPL.

Unfortunately, the comet also ‘takes the plunge’ sunward in early September, and passes only 12 degrees from the Sun in mid-September before heading southward. It’ll also juuuust miss the joint NASA/ESA SOHO’s LASCO C3 field of view.

Too bad it didn’t come by in December, as it would’ve passed just 0.06 AU (9 million kilometers or 5.6 million miles) from the Earth, and would’ve been a truly spectacular comet.

Keep in mind, as of writing this, the NASA/JPL ephemeris for the orbital solution for the comet is only from 63 observations over a four day span; expect the final orbit for the comet to get tweaked a bit as its path and position through space is better known (it’s that new!) P1 Nishimura crept up on us from south and sunward, which is most likely how it evaded detection earlier this summer.

On a steep orbit inclined 129° relative to the ecliptic plane, Comet P1 Nishimura is on a retrograde path. This means its moving opposite to the planets in the inner solar system. The comet also looks to has an orbital eccentricity of slightly greater than 1.0, meaning it’s most likely a dynamically new visitor to the inner solar system from the distant Oort Cloud, due to get ejected towards galactic space in the direction of the southern constellation Pyxis after perihelion.

How Bright?

As a first time newcomer approaching the Sun, P1 Nishimura could prove to be an active one, another plus. Late August sees the comet 20° above the eastern horizon one hour before sunrise as seen from latitude 35° north. Also, watch for a brilliant crescent Venus entering the dawn view. Venus is fresh off of inferior conjunction on August 13th. We’re seeing the comet approaching the Sun on a nearly perpendicular path from our Earthbound perspective. This is an ideal geometry to spy a dust tail, should the comet sprout one towards perihelion.

The apparent path of Comet P1 Nishimura through the dawn sky from August 17th through September 7th as seen from latitude 35 degrees north. Note that the background celestial view is for the end of the path. Credit: Starry Night.

The comet then begins its dramatic plunge towards the eastern horizon in early September, becoming increasingly difficult to observe. The following evening apparition will be a brief and bashful one for northern observers. The comet only climbs 5° above the western horizon, 30 minutes after sunset around September 16^th as seen from 35° north.

The Comet Month by Month

Here’s a look at celestial dates with destiny for Comet P1 Nishimura over the next few months. Unless otherwise noted, ‘near’ denotes a pass or conjunction of less than one degree, or the diameter of two full Moons.

August

19- Passes 16’ from the ‘Clown Face’ Nebula NGC 2392.

22- Crosses the ecliptic plane northward.

26- Crosses into the constellation Cancer.

31- Passes 4 degrees from the open cluster Messier 44.

The celestial path of Comet P1 Nishimura, through October 1st. Credit: Starry Night.

September

5-Crosses into the constellation Leo.

7-Passes near the +3^rd magnitude star Epsilon Leonis.

9-Passes near the +3.4 magnitude star Zeta Leonis.

13-Earth closest approach at 0.29 AU distant.

15-Passes in front of (transits) the +2nd magnitude star Denebola (Beta Leonis).

16-Crosses into the constellation Virgo, and reaches a minimum elongation of 12 degrees from the Sun.

18-May top out at +2^nd magnitude, as the comet reaches perihelion at 0.22 AU from the Sun.

21-Crosses the celestial equator southward.

24-Crosses the ecliptic southward.

October

1-Drops below +10^th magnitude.

Farewell For Comet Nishimura

From there, the comet begins its long journey out of the solar system. Southern observers may still see Comet P1 Nishimura as it departs, never to be seen by human eyes again.

The projected light curve for Comet P1 Nishimura. Adapted from Seiichi Yoshida’s Weekly Information About Bright Comets.

Your best bet at spotting Comet P1 Nishimura is to sweep the suspect area of sky with binoculars, or a low power telescopic field of view. Watch for a fuzzy blob that refuses to snap into focus. COBS (The Comet Observer’s Database) is an excellent source to see what the comet is currently doing, and Heavens Above will generate wide and narrow field of view finder charts for the comet. Gideon van Buitenen’s comet page will also produce inverted finder charts (black stars on a white background) for a given comet.

Though +6^th magnitude is usually quoted as the cut off for naked eye visibility, comets are diffuse objects. In past experience, comets like F3 NEOWISE in 2020 only became conspicuous objects able to be captured along with foreground objects when they hit brighter than +3^rd magnitude or so.

The hunt is now on, to nab Comet C/2023 P1 Nishimura in the dawn sky.

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