Neowise: what is a comet and how do you see it?
In recent weeks, a new star has appeared in the sky: it is comet C / 2020 F3 (NEOWISE), or simply Neowise. It was detected in March 2020 by the Neowise probe and the comet has been visible in the sky since June 2020 and for a few more weeks.
A comet, unlike a meteor, is not stealthy and returns periodically. In addition, they are much rarer to observe. A comet easily visible to the naked eye is a unique phenomenon in a generation, while it is possible to see meteors almost every night (some more than others).
What is a comet? Where are they from?
A comet is not a meteor. The meteor is a small piece of rocky debris (a few meters to a few tens of meters in diameter) that passes through the Earth’s atmosphere and burns in a few seconds due to heating due to the friction of the air. Usually it burns completely, but if there is anything left that falls on the ground, it forms a rock which is called a meteorite.
Comets, on the other hand, are not rocky, nor do they pass through the Earth’s atmosphere.
These are debris of ice (water and frozen gas, as well as dust) only a few kilometers in diameter and which come to us from the confines of the solar system: from the Kuiper belt or the Oort cloud, so well beyond Pluto’s orbit.
These two regions are reservoirs for several billion of this ice debris. From time to time, gravitational disturbances of the planets, as well as collisions, cause one of them to begin a progression towards the inner solar system: a journey that lasts several thousand years.
This is when they become visible: as they approach the Sun, the ice gradually sublimates and the ice cube leaves behind a trail of vapors and dust. Solar winds push these vapors towards the back of the comet, forming a “hairline” that is always facing the Sun.
Generally, once passed close to the Sun, the comet, having gained strong speed, is gravitationally catapulted from where it came. Since it remains a star like any other, if it is not destroyed or deflected in the meantime , it will return periodically.
The very famous Halley’s comet, known for thousands of years, is visible every 76 years. The next time will be in 2061. Halley in 1705, scanning the historical writings, noticing that a star was visible at very regular time intervals. Understanding the recent laws of Newton and Kepler, he deduced that these phenomena were in fact the same every time. He was also able to predict the date and the position in the sky of his next visit. He died before, but his prediction came true with incredible accuracy, and this fact was a hallmark of science, astronomy, and physics at the time.
What does a comet look like?
Comets, as I have said, are blocks of ice and dust “only” in diameter a few kilometers. They are therefore absolutely tiny in front of the planets. Since they also come from the far reaches of the solar system, detecting them in advance is therefore impossible.
It is only as they approach the inner solar system that we begin to be able to detect and then see them. Neowise was thus detected for the very first time in March 2020, to be visible to the naked eye from June 2020.
And again: what we see is not the debris of ice itself, but the impressive hairs of the comet. This is made up of gas and dust blown by solar winds, and it is several million kilometers long!
In fact, comets generally have two different hairs of different origins.
The main one, which is easily seen and curved, is the trail of dust that the Sun blows from the debris of ice. This hair, generally white, takes the shape of the path of the comet in the sky.
The secondary, much paler, but colored blue or red depending on the composition of the ice corresponds to gases ionized by charged particles from solar winds. A bit like the polar lights. This tail is diametrically opposed to the Sun.
It’s like running in the dust: the dust cloud follows your path, while your shadow is always directed in the opposite direction to the Sun, no matter which direction you are going.
How to see Neowise?
This comet has been visible for a few weeks. Like the planets Venus and Mercury, it is currently closer to the Sun than the Earth, and is therefore visible either when the Sun has just set or just before it rises.
In this case, on July 18, 2020 in France, it is visible from late evening until dawn (but after 5 a.m., the incipient glow of the Sun prevents us from seeing), direction North-East and not too far from the ‘horizon. As a reminder: the Sun rises in the East, and the Big Dipper is in the North: so it is at the place where the Sun will appear that we must look, then a little to the left.
Throughout the end of July, the comet should be visible to the naked eye.
You will hardly be able to miss it until ~ 5am, not too far from the horizon. Beyond that, it is gradually dazzled by the radiance of the Sun and ends up not being visible.
In summary, if you want to observe it:
go out at 4-5 a.m., prefer to arrive earlier than too late (or at midnight, when it’s dark);
choose a high and clear location: you should be able to see the horizon (a hilltop is perfect);
a place out of the city’s light pollution;
take binoculars (even the most mundane you have), and if you obviously have a refracting telescope or a small telescope.
Quick tip: A powerful laser pointer can help you spot what you’re looking at, or teach your kids where to look. But if there are other spectators around, make sure you don’t obstruct them (the laser will get in the way if they take long exposure photos) or abuse them.
Finally, these days, if you go out to observe the comet in the northeast in the morning, don’t forget to look south to see the very bright Jupiter as well as Saturn.
Jupiter, through an instrument will be accompanied by its 4 Galilean moons (which are visible with simple binoculars!), And Saturn, with a little luck, will show its rings.
