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Comet Nishimura is brightening and moving fast: See it now!
It’s already been a good year for comets — and it just got astronomically better. A newly discovered comet is poised to wow us in the coming week: Comet C/2023 P1 (Nishimura). It’s already readily visible and the best views are just days away.
Japanese amateur astronomer Hideo Nishimura discovered the new comet August 12 near the star Zeta (ζ) Geminorum in Gemini the Twins, according to Seiichi Yoshida’s page on the object. At that time, the comet was already magnitude 10.4 and closing in on the Sun at a distance of just 1 astronomical unit, or AU (1 AU is the average Earth-Sun distance). Nishimura is continuing into the inner solar system on its way toward perihelion, the closest point in its orbit to the Sun. It will reach that point in less than two weeks, on September 17, when it will swing around our star at a distance of just 0.23 AU — some 40 percent closer to the Sun than the planet Mercury.
Along the way, Nishimura is expected to brighten rapidly, potentially reaching magnitude 2. Although that should be an easy naked-eye magnitude, the comet’s low altitude in the Northern Hemisphere means it’s really best seen with binoculars or a telescope. But through those optics, it will dazzle. Keep reading to learn where it is now, when to view it, and what to look for.
How to see Comet Nishimura
Comet Nishimura is now visible in the predawn skies for Northern Hemisphere observers. It’s rising later each morning as it tracks quickly through the stars of Leo the Lion. On September 7, it will rise around 4:20 A.M. local daylight time. By Sunday morning (the 10th), it will rise around 5 A.M. local daylight time. This is because the comet is rapidly approaching the Sun, so it appears to be moving quickly through our sky. By perihelion, it will rise with the Sun and won’t be visible at all (or again) above the equator.
What this means is, now is the time to see it!
Step outside an hour before sunrise tomorrow morning and you’ll see the front half of Leo rising above the eastern horizon. Look for the bright star Regulus (magnitude 1.4), which is just 2° high at that time. (Don’t confuse it for blazingly bright Venus, which is magnitude –4.8 and much higher in the east to Regulus’ far upper right, in Cancer.) Fortunately, Nishimura is a bit higher than Regulus: On the 7th, it is 12° high an hour before sunrise, located 1.7° due east of 3rd-magnitude Epsilon (ϵ) Leonis, the endpoint of the curve that forms the famous Sickle asterism.
But Nishimura is moving fast. It will continue tracking east, “falling” toward the Sun in the predawn sky. It passes less than 3° north of Gamma (γ) Leonis on the 9th and then slips 1.5° south of Delta (δ) Leonis on the 12th. By the 12th, the comet will rise around 5:40 A.M. local daylight time, almost exactly an hour before sunrise. You can try to spot it some 4.5° high 30 minutes before the Sun peeks above the horizon. The comet will be about 15° northeast of (to the left and slightly above) Mercury, which by that time will be magnitude 2.7 and 3° high.
From there, Nishimura will slide just under Denebola, the star marking Leo’s tail, and cross into Virgo on the 15th, which is likely the last day Northern Hemisphere observers will be able to catch it. After that, it will be too close to the Sun for observation.
A bright comet
Although the comet will be dropping lower each morning as the sky grows brighter, there’s an important caveat: Nishimura will be growing brighter as well. Observers are currently reporting on the Comet Observation database (COBS) that Nishimura is 5th magnitude, and it’s predicted to reach magnitude 2 to 3. Stunning astrophotos are already circulating, featuring the comet’s glowing green head and long, thin tail.
Although its diminishing altitude in the brightening morning sky reduces the likelihood of spotting it with the naked eye even at its brightest, Nishimura should remain readily visible in binoculars or any small telescope. It’s also an excellent target for astrophotographers; if you’re interested in how to best photograph the comet, we’ve got advice for photographing comets from highly experienced astrophotographer Damian Peach. (You can send your photos to readergallery@astronomy.com; we’d love to feature them online or in print!)
While observing Nishimura, always take care to stop viewing through binoculars or a telescope several minutes before the Sun rises from your location — and note the time of exact sunrise will vary by location, so check this information specifically for your observing site.
Comets are unpredictable objects, and Nishimura has never been identified before. It may or may not survive its close trip around the Sun, and it may or may not brighten as expected during that time. There’s always the chance it could outburst and brighten suddenly or even more than expected, as 12P/Pons-Brooks did in July.
If all goes well, Nishimura will swing past the Sun and quickly head back for the outer reaches of the solar system, never to return. Although it came from our Oort Cloud, it’s now a hyperbolic comet, meaning it has enough energy to escape the Sun’s gravity and rocket off into interstellar space. So now is truly your best — and only — time to see it. Get out there!
注释：
Geminorum: adj
表示" 双子座Gemini的所有格"，如：Zeta Geminorum stars 双子座S型星
Gemini: n
表示" 双子座；【天】双子宫"，如：A constellation in the Northern Hemisphere near Leo and Gemini.巨蟹星座北半球狮子座和双子座附近的一个星座
perihelion
表示" 近日点；最高点"，means "periapsis in solar orbit; the point in the orbit of a planet or comet where it is nearest to the sun"，如：A comet is at perihelion when it is closest to the sun. 彗星最接近太阳时，它就是在近日点。
Regulus: n
表示" 狮子座的一等星；熔渣"，means "the brightest star in Leo"，如：That's because Regulus routinely pairs up with the moon and planets on the dome of night. 这是因为它经常和月亮以及夜晚苍穹上的其它行星结成一对。
asterism: n
表示" [天]星群；[印刷]三星符号"，means "(mineralogy) a star-shaped figure with six rays that is seen in some crystal structures under reflected or transmitted light"，如：In Greek myth, the Big Dipper asterism represents the hindquarters and tail of the constellation Ursa Major, the Great Bear. 在希腊神话传说中，北斗七星的三星符号象征着大熊星座的后臀和尾巴。
Denebola: n
表示" 狮子座中的第二明星"，means "a star in Leo approximately 43 light years from Earth"，如：A constellation in the Northern Hemisphere near Cancer and Virgo, containing the bright stars Regulus and Denebola. 狮子（星）座北半球的一个星座，位于巨蟹座和处女座附近，包括两颗明亮的星：轩辕十四和天津四
caveat: n
表示"防止误解的说明；警告"，means "a warning against certain acts"，如：I would offer a caveat for those who want to join me in the dual calling. 为防止发生误解，我想对那些想要步我后尘的人提出警告。
astrophoto: n
表示" 天体照片"
hyperbolic: adj
表示"夸张的；双曲线的"，如：Karl Gauss pioneered hyperbolic geometry. 卡尔·高斯开辟了双曲线几何学。
中文简要说明：
日本天文学家西村荣男在今年8月12日发现的C/2023 P1，或称西村彗星（Nishimura）正接近地球。预计这颗彗星将在9月12日达到最接近地球的位置，然后在9月17日达到最接近太阳的位置。报导称，错过这一次，要再等300年，而美国天文杂志报导，西村彗星很有可能会摆脱太阳系的重力陷阱，一去不复返。
综合《天文学》（Astronomy）杂志、台南市教育局新闻稿，西村彗星被归类为一颗周期性彗星，因为它大约每300年才一次经过太阳。当它在9月12日抵达近地点时，它将位于狮子座，距离地球约0.84（AU）天文单位，并且其视星等约为2.7。
西村彗星之后将在9月17日抵达近日点，位于处女座，距离太阳约0.22天文单位，其视星等约为1.7。在这个时候，它将非常接近太阳，距离约为12.2度左右，所以在日落时分，人们将能够看到它在天空中的踪影。目前，人们已经可以在凌晨使用望远镜进行长时间曝光，以拍摄西村彗星的影像。
《天文学》杂志报导，如果一切顺利，西村彗星将绕过太阳，迅速返回太阳系的外围，再也不会回来。虽然它来自我们的奥尔特云（Oort Cloud），但它现在是一颗双曲线彗星（hyperbolic comet），这意味着它有足够的能量来逃离太阳的引力，并进入星际空间一去不复返，想看可要把握机会了。
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