Despite the large space comet ZI/ATLAS approaching Earth at high speed, its brightness has been noticeably decreasing in recent days. The "Interfax" report, based on data from the Russian Space Research Institute, provides clear explanations for this strange situation.
According to the Solar Astronomy Laboratory, the comet's stellar magnitude - that is, the main brightness measurement indicator of celestial bodies - varied from 10.1 to 10.6. This means that the brightness has decreased by almost 63% compared to six days ago.
At first glance, this situation seems incomprehensible: because the comet has reduced its distance from Earth by 10 million kilometers, but in places where its brightness should have increased, it has decreased instead. According to experts, the main reason is that the comet is gradually moving away from the Sun.
Comets appear sparkling only when reflecting sunlight. For this reason, it is very common to observe a natural decrease in brightness when the amount of light coming from the Sun decreases. Astronomers are not denying internal processes either: for example, changes in the physical structure of the comet's nucleus can affect albedo - that is, its ability to reflect light - and reduce its apparent brightness.
Nevertheless, ZI/ATLAS remains one of the most prominent comets in the sky. Among hundreds of space objects available for observation, it ranks fourth. Comet C/2025 A6 (Lemmon) is at the top of the ranking - it is also known for its relatively bright appearance, although it has dimmed tenfold in the last month.
ZI/ATLAS was first detected on July 1 of this year. Researchers have confirmed that its origin belongs to other star systems. Interestingly, the comet's age has been determined to be more than 7.5 billion years, which is approximately 3 billion years older than the Sun. This makes him one of the oldest visitors to the universe.
In general, ZI/ATLAS is a very unique object not only geophysically, but also from the point of view of astronomical history. It's natural to watch with great interest how its movement and brightness will change in the coming weeks.
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