Ceres and Vesta come very close in the night sky

The two largest asteroids, Ceres and Vesta, are currently heading for their closest encounter in the night sky in recorded history. And you can see them in binoculars.

Paths of Ceres and Vesta
Wide-angle view of the paths that Ceres and Vesta take during the first week of July in their closest ever encounter. The bright red “star” is Mars. Credit: Paul Sutherland/Skymania

The two bodies will lie just 10 minutes of arc apart, which is only a third the apparent diameter of the Moon. Though both lie in the main asteroid belt, the spectacle is due to our line of sight.

Both occupy the same region of space every 17 years or so, but they normally lie several degrees apart, so to be so close is extremely rare and has not happened at all before since the telescope was invented.

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Ceres is the larger of the two asteroids. It was the first ever to be found, by Giuseppe Piazzi, a Sicilian monk, while checking the sky at Palermo Observatory on New Year’s Eve, 1800. In 1996 it was promoted to dwarf planet by the International Astronomical Union at the same time as Pluto was demoted from being a full planet to the same status.

Paths of Ceres and Vesta
Close-up view of the paths of Ceres and Vesta during the first week of July. Credit: Paul Sutherland/Skymania

Vesta was the fourth planet to be discovered, in 1807, and though smaller than Ceres it is the brightest in the sky.

During this conjunction, it will appear at magnitude 7.1, much brighter than the more distant Ceres at magnitude 8.4. Both are too small to appear as any more than points of light through binoculars or a small telescope.

From northern latitudes, where the nights are short in summer, you will need to observe as soon as the sky gets dark because this part of the sky is then sinking low towards the horizon.

Watch fron ome night to another and you will see a classic example of how the sky is ever-changing, with the two asteroids coming close and then moving apart again.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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