We are now close to the moment of truth for the comet C/2023 A3 (Tsuchinshan-ATLAS)renamed “comet of the century” due to the great expectations surrounding the brightness it could reach in our skies. The comet is close to perihelion (the point in its orbit at its minimum distance from the Sun), which will occur on September 27th when it will be only 58 million km from our star, approximately equal to the average distance between Mercury and the Sun. The passage at perihelion will represent the watershed in the life of this icy object from the cold outskirts of the Solar System: if the object were to survive the close encounter with the Sun, then there would be excellent possibilities to transform the journalistic term “comet of the century” in realityThe comet is currently visible only from the southern hemisphereshortly before sunset, while it will become visible in our skies around the October 10tha few days before the moment of maximum approach to Earth of the October 12thapproximately 70 million km from our planet. If the comet were to survive we could witness a unforgettable show at sunset, with the comet visible to the naked eye in a westerly direction.
How and When to Observe Comet C/2023 A3
The comet C/2023 A3 (Tsuchinshan-ATLAS) is currently visible only from the southern hemispherelocated between the constellations of Sextans and Hydra. It rises at dawn, around 4:40 in the morningabout an hour and a half before sunrise. The comet is currently magnitude equal to 4so in theory visible to the naked eye (which occurs below magnitude 6 in a sky free of light pollution). However, its visibility window is very narrowsince at that time the sky begins to lighten with the approach of dawn. Binoculars or a telescope are therefore necessary to be able to spot it towards the east.
Once perihelion has passed, the comet will slowly move away angularly from the Sunbecoming around October 10 visible in our hemisphere if it survives the close encounter with our star. On October 10, the comet will set just under forty minutes after the Sun, consequently it will be visible for a very short time and a lot low on the western horizon. As the days pass, however, the increase in angular distance from the Sun will cause the comet to sunsets ever laterthus increasing its time of presence in the sky after sunset. October 15thfor example, the comet will be found 20° above western horizon after sunset, remaining in the sky for a full two hours after sunset.
If it were to survive the close encounter with our star, it would be visible to the naked eye towards the westbetween the constellations of Bootes and Ophiuchus: a show definitely not to be missed. As always, we recommend using binoculars to fully appreciate the celestial event.
What are the brightness forecasts?
The brightness forecast of the comet are based on theoretical models that astronomers have formulated about these celestial objects. C2023/A3 (Tsuchinshan-ATLAS) is a comet in first pass through the inner Solar System and it is defined non-periodicthat is, it has an orbital trajectory that takes it through the inner Solar System only once and then accelerates thanks to the gravitational slingshot effect of the Sun and exits the Solar System forever.
Therefore, without information from previous passages, as in the case of periodic comets such as Halley’s Comet, it is difficult to predict whether it has the right characteristics to survive the perihelion passage. The excessive sublimation of the cometary nucleus (i.e. the transformation of volatile ices into gases due to solar heat) due to intense solar radiation can in fact lead to premature breakup of the comet.
So far the comet is living up to astronomers’ predictions about increasing brightness. perihelion is expected for the September 27thwhen the comet will pass at a distance similar to that of Mercury from the Sun, that is, approximately 58 million km. If it manages to survive the perihelion, we will see the comet reappear on the other side of the Sun and reach its maximum proximity to our planet on October 12thto 70 million km from Earth.
In those days, some visibility forecasts report that comet C/2023 A3 (Tsuchinshan-ATLAS) could become bright as Saturnor even like Venus, which is the brightest celestial body in our sky after the Sun and the Moon. This is due to the particular geometric configuration that will occur after the comet’s passage through perihelion, when it will be practically between the Earth and the Sun. In this case the phenomenon of forward scattering (“forward spread”) which would make the comet, backlit by the Sun, appear significantly brighter. The dust and ice crystals surrounding it would scatter the light in the direction of the observer, increasing Like this the brightness. We can only wait to see the comet reappear on the other side of the Sun to understand if it really will be the “comet of the century”, because as we know: “Comets are like cats, they have tails and do exactly what they want.”
Where does comet C/2023 A3 come from?
Comet C2023/A3 is a comet non-periodic characterized by ahighly inclined orbit relative to the plane of the Earth’s orbit. These two characteristics are typical of comets originating from Oort clouda remote spherical region surrounding our Solar System and extending between the 2000 and 200,000 astronomical units (an astronomical unit is the average distance between the Earth and the Sun, equal to approximately 150 million kilometers).
The Oort cloud is generally considered a “reservoir” of comets. In fact, in this area the remains of the formation of the Solar System are preserved, icy bodies such as asteroids and comets that due to gravitational perturbations can enter the internal Solar System and collide with other celestial bodies. The objects of the Oort cloud are rich in volatile elements, so when they approach the Sun they sublimate quickly and sometimes they do it so suddenly that it leads to cometary nucleus collapse.
