Comet Leonard to light up the December sky

Because comets don’t come along all that often, they are ingrained in folklore, with few things being more Christmassy than a comet lighting up the December sky. The talk amongst astronomers is that Comet Leonard will be visible to the naked eye on the nights of December 12 and December 13.

It will be at the point of its orbit during these two nights, which is closest to the earth, passing only 35 million kilometers from us. Of course, unfortunately, distance is not the only important thing in determining whether Leonard will light up the sky this Christmas. Let’s go by parts. First of all … What is Leonard?

What is a comet?

C / 2021 A1 Leonard is his full name, and that C denotes that it is a comet. This means that, unlike meteoroids and asteroids, comets are (generally) brighter and more colorful. They exhibit a head of hair surrounding their most brilliant point and a pair of tails. While shooting stars ( meteors that pass through the atmosphere) only last a few tenths of a second, they remain visible for several nights because they are much further away from us, appearing to move much slower. In fact, Leonard is already visible from some places, such as the Canary Islands, if the night is clear and a telescope or binoculars with sufficient resolution are used.

However, beyond their appearance in the distance, the differences between comets and asteroids are many. One of the most important is, for example, its composition. Comets consist of mostly ice and dust, maybe even some rock. Because of this mixture of dust, water, ice, and gases, comets leave a trail that forms one of their two tails. Meanwhile, the heat of the Sun transforms its ice into gases that will wrap its core, creating the so-called hair or coma. The second tail is formed by the pressure exerted by the Sun’s radiation on the ice particles, pushing them away from the star. The first tail glows with a bluish hue and much more intensity than the dim second tail, so, with the naked eye, we usually only see one tail from the earth.

Finally, and this fully applies to Leonard, while asteroids and meteoroids tend to come from the asteroid belt that stretches between Mars and Jupiter, comets tend to come from the much more distant Oort cloud. It is estimated that Leonard began his journey about 40,000 years ago, from these remote places where the solar winds could not sweep the icy water accumulated in those small objects of the solar system. And that is precisely one of the problems we have with Leonard, having a high part of ice; its journey into the solar system could be evaporating it. There have been reports that its brightness is getting dimmer. In any case, it is too early to say so, but if it were true, it could affect the observation of the 12th.

The comet’s distance is essential, but in reality, some characteristics determine its brightness (surface, size, etc.) And it is that aspect, which we call magnitude, that is the one that interests us the most to predict whether it can be seen or not by the naked eye. Leonard’s magnitude is currently above seven, and it will need to shrink quite a bit to be visible. Specifically, it should be below six to be seen with the naked eye on a cloudless night with a clear horizon. We cannot know yet, but it is a possibility to consider.