The Intriguing Appearance of Comet Nishimura: Insights from an Authority on What to Anticipate

The newly-identified Comet Nishimura, designated as C/2023 P1, has captured public intrigue. Although its calculated path indicates a near pass to the Sun and a potential to be seen with the unaided eye, the likelihood of an exceptional celestial display, akin to the vivid illustrations circulating, is minimal.

Among the celestial objects that populate our Solar System, great comets are perhaps the most awe-inspiring when they sporadically illuminate our sky. Recent social media discussions have been rife with articles suggesting that we are currently witnessing such an event, identified as C/2023 P1 or Nishimura.

As of the time of writing, Comet Nishimura is making its first appearance in over four centuries. It was discovered on August 12 by Japanese astronomer Hideo Nishimura. Subsequent to the discovery, archival images of the celestial body, tracing back to January, were located. These images assisted astronomers in determining the comet’s trajectory.

Analyses revealed that Nishimura will come closer to the Sun this month than Mercury’s orbit. Based on its observed luminosity at the time it was discovered, it is possible that the comet could become visible without the aid of telescopic instruments. Yet, will it dazzle us with a celestial spectacle? The prospects appear limited.

Captured on August 18, an image from June Lake, California, showed Comet Nishimura featuring a green coma and a slender tail. Credit & Copyright: Dan Bartlett

Regrettably, the comet’s trajectory will keep it near the Sun as viewed from Earth. Even though it has sufficient brightness to be perceptible to the naked eye under dark conditions, at most it will appear close to the horizon shortly after sunset, nearly engulfed by solar glare.

Nevertheless, the global scientific community remains enthusiastic. Even a celestial object that is challenging to observe with the naked eye merits attention. To quote science writer and astronomer David H. Levy, “Comets are like cats: they have tails, and they do precisely what they want.”

The possibility remains that Nishimura could become unexpectedly brighter in the forthcoming weeks. If not, we may have another opportunity next year, a topic that will be expanded upon later.

Factors Influencing a Comet’s Brightness

In the remote icy expanses of space, comets are fundamentally conglomerates of ice, dust, and rock—residual material from the Solar System’s formation. As a comet nears the Sun, thermal activation occurs on its surface, causing near-surface ices to sublimate, converting into gas and ejecting from the comet. This gaseous outflow carries dust, cloaking the comet’s nucleus in a nebulous cloud termed a “coma.”

Solar winds then expel this gas and dust away from the Sun, creating the comet’s tail, which invariably points away from the Sun. The comet’s visible aspect is sunlight reflecting off the coma and tails, as the nucleus remains concealed. A comet’s luminosity typically depends on the following parameters:

• Nucleus size: A larger nucleus usually equates to a more expansive active area, leading to greater gas and dust emission.
• Proximity to the Sun: Closer proximity results in increased activity and luminosity.
• Distance from Earth: A closer approach to Earth makes the comet appear brighter.

Prospects for Nishimura

In the case of Comet Nishimura, it seems likely that its dimensions are not particularly large; otherwise, it would have been detected earlier. It is not exceedingly near Earth, but it will pass relatively close to the Sun, reaching peak activity around its perihelion. Even though it will remain adjacent to the Sun in the sky, which makes it less than ideal for viewing, the prospect remains tantalizing.

The best window for observing Nishimura from Australia will occur between September 20 and 27, when it sets about an hour post-sunset and will be at its maximum distance from the Sun in the evening sky on September 23. But given its location and solar proximity, it may well be obscured by the Sun’s glare.

Some comets disintegrate when they are nearest to the Sun, thereby considerably brightening. However, the likelihood of this occurring with Nishimura is low, as it has an orbital period of approximately 430 years, suggesting it has made numerous solar passes without disintegrating.

Yet, the tail might still be perceptible as dusk ensues. Before vanishing into the northern hemisphere’s solar glare, the tail was estimated to be around six degrees in length, a measure likely to increase as it approaches the Sun.

The Next Prominent Comet

Should Nishimura not meet expectations, Comet C/2023 A3 (Tsuchinshan-ATLAS), discovered early this year and currently situated as far from the Sun as Jupiter, is showing promise. Over the next year, it will approach the Sun, coming closest in late September 2024. If it behaves predictably, it could deliver a truly grand spectacle. However, one should always bear in mind: comets are like cats.

Author: Jonti Horner, Professor of Astrophysics, University of Southern Queensland.

Adapted from an article originally published in The Conversation.

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More about Comet Nishimura

• The Original Article on Comet Nishimura
• About Cometary Brightness Factors
• Introduction to Celestial Phenomena
• Understanding Comets: A Scientific Overview
• Comet Observation Techniques
• The Solar System and Its Objects
• Profile of Astronomer Hideo Nishimura
• Upcoming Celestial Events: A Calendar
• Glossary of Astronomy Terms
• Current Research on Comets