Comet Nishimura as seen in L’Aquila, Italy, on 8 September
Lorenzo Di Cola/NurPhoto/Getty Images
You have a short window of opportunity to see the comet Nishimura in the sky before it retreats to the outer solar system, not to return for 400 years.
Nishimura was first spotted on August 12 of this year, drawing the attention of astronomers around with its peculiar green glow. It was seen in the northern hemisphere a couple of hours before sunrise in the days leading up to the close encounter with the sun on September 17th.
Comets are dirty snowballs because they are composed of rock and ice; but, when they approach the Sun, a significant portion of the ice changes into a charged gas called plasma, which then forms the comet’s tail. The comet came within 33 million kilometres of the surface of the sun, causing widespread concern about its chances of survival.
Don Pollacco of the University of Warwick in the UK notes that “some do not survive,” meaning that they can simply vanish. Comet Nishimura was spared this fate, thankfully. To re-approach the sun, it will take 400 years, so “it is now receding from the sun and heading back into the cold depths of the solar system,” as Pollacco puts it. “We have one last opportunity to see Nishimura before it vanishes forever.”
An powerful solar storm slammed Nishimura during its close approach. The comet’s plasma tail was disconnected from the comet for a short time due to a burst of charged particles from the sun. However, a 2018 laboratory study suggested that an electrostatic field produced by the interaction of the plasma and the solar wind may be to blame.
Diatomic carbon, which consists of two carbon atoms bonded together, gives the coma, the atmosphere around the nucleus, its distinctive green colour.
For the next few days, if you live in the northern hemisphere and want to witness this for yourself, you can find it low on the horizon immediately after sunset. As soon as the sun goes down, look to the west horizon, and you’ll see Mars, with Nishimura to its right.
Those in the southern hemisphere will have a little more time, maybe a week or so, to witness the comet. As the sun sets, it will join Mars in the west, although it will be far lower in the sky.
Even though “some reports say it can be seen by eye,” Pollacco recommends using binoculars. After this, it will become increasingly difficult to see without a telescope.
Q1: When was Comet Nishimura discovered?
A1: Comet Nishimura was discovered on 12 August this year, with its unique green glow catching the attention of astronomers worldwide.
Q2: How close did Comet Nishimura come to the sun?
A2: It passed within 33 million kilometers of the sun, making its closest approach on 17 September.
Q3: What causes a comet’s tail to form?
A3: Comets are made of rock and ice, and when they approach the sun, the ice turns into a charged gas called plasma, creating the comet’s tail.
Q4: Was there uncertainty about Comet Nishimura’s survival during its close encounter with the sun?
A4: Yes, there was uncertainty, as some comets do not survive such encounters. Fortunately, Comet Nishimura did.
Q5: Why is Comet Nishimura green?
A5: Comet Nishimura appears green due to the presence of diatomic carbon, a relatively rare carbon gas, in its coma.
