After putting on a show around ten days ago, particularly in the southern hemisphere, comet Tsuchinshan-ATLAS arrived early at night in the northern hemisphere this weekend. Le Figaro explains how to observe it.
Making cometary forecasts is always a delicate exercise. Many parameters come into play to predict the light intensity of a comet. Especially when it is its first passage close to the Sun, as is the case for Tsuchinshan-ATLAS, discovered only in January 2023.
A little reminder for neophytes: a comet is a small frozen body of only a few kilometers which has the particularity of vaporizing when it approaches the Sun, to the point that it becomes gigantic in appearance, with a hair (coma) that can measure tens of thousands of kilometers and an even longer tail. This can thus form a spectacular spot in the sky.
The vaporization phenomenon intensifies as the cometary nucleus approaches the Sun, then it gradually decreases as it moves away from it. In this case, Tsuchinshan-ATLAS passed its closest point on September 27. It was then already visible to the naked eye in the southern hemisphere, giving rise to some magnificent photos, like those taken by photographer Luc Perrot in Reunion:
If cometary activity is maximum near perihelion, the luminosity of the phenomenon seen from Earth can be even more intense. On the one hand because the comet can continue to approach us, and on the other hand because the geometric configuration in relation to the Sun is more or less favorable. In recent days, for example, the light coming from the Sun is scattered by its cloud of gas and dust, which gives it a particularly intense shine.
In recent days, the comet has entered the field of view of the Soho solar observation satellite, whose receivers it is almost saturating. Its magnitude is equivalent to that of Venus, the brightest star in the sky. Currently, it could almost be visible in broad daylight (if it wasn’t so close to the sun…).
This peak in brightness is, however, transient. “This highlighting phenomenon will not last and the brightness of the comet will quickly diminish”warns Nicolas Biver, astronomer at the Paris Observatory, specialist in comets. “But in all likelihood, it should remain visible to the naked eye for a few days at least.” The spectacle could be comparable, or even a little more impressive, than the comet Neowise which was visible in the summer of 2020 in mainland France.
In practice, you will have to look due west, at dusk. “It will be just visible to the naked eye above the horizon on Friday evening around 8 p.m.*”explains Nicolas Biver. “If the weather is good, you’re somewhere in the mountains with a clear view to the west, you might be able to see it. » For others, it is better to wait until Saturday or Sunday evening to have a chance to observe it. The comet will be a little higher each day, slightly further south, and will set about 20 minutes later.
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As a guide, she will go to bed after 10 p.m. from October 18 to 20. “It is an all the more favorable window for observation as the moon will not yet have risen”explains the French astronomer. “But its magnitude will then have diminished greatly. » The tenuous balance between its position in the sky, astronomical conditions and the intrinsic brightness of the comet will be subtle. The most limiting parameter could in fact be the weather… In short, take advantage of any cloudless evening over the next ten days to find a clear observation location towards the west and as spared as possible by light pollution .
*Paris time. It takes about half an hour to Strasbourg, half an hour to Brest.
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