CAN URANUS BE SEEN WITH THE NAKED EYE?

In ancient times, people could only study the sky with their eyes. Thus, knowledge of the universe was limited to objects that could be seen with the naked eye. Most of these objects were stars.

Although it was not known when, where, or by whom, at some point someone realized that in the midst of all the stars there were a few bright points that moved across the sky, changing their position from day to day. Such points were called planets, from the Greek word for "wandering stars.

The ancients thus discovered Mercury, Venus, Mars, Jupiter, and Saturn, all bright enough to be easily seen without the aid of instruments. The fainter Uranus and Neptune, on the other hand, were not discovered until centuries after the invention of the telescope.

In fact, under favorable conditions, that is, when its distance from Earth is not too great, Uranus has an apparent magnitude that varies between +5.5 and +6.0, above the theoretical limit of visibility to the naked eye of +6.5.

Although it is visible to the naked eye, we should not be surprised that Uranus was not discovered before the invention of the telescope.

In fact, a perfect and very dark sky is required to observe it. Light pollution was obviously not present at that time, but other factors contribute to the brightness of the sky, most notably the Moon. 

The various telescopes and binoculars did not exist at that time, so you had to rely on your eyes. You had to have perfect eyesight to see an object as faint as Uranus.

Nevertheless, it is quite likely that Uranus was observed with the naked eye before its discovery. However, because it is so far from the Sun, Uranus moves very slowly through space, and therefore its motion along the sky is minimal.

Because of its low brightness and very slow motion, it is often mistaken for a fixed star. This is how Uranus escaped detection by ancient astronomers.

Credits: NASA, ESA, Hubble.