September 11 – Messier 2

M2, or NGC 7089, is a globular cluster of about 150,000 stars in Aquarius. It was discovered twice: firstly by Jean-Dominique Maraldi on September 11th 1746, and again on the same date 14 years later (1760) by Charles Messier.

Messier 2 (aka NGC 7089)
Messier 2 (aka NGC 7089)

M2 is fairly large, as globular clusters go, at 175 light years across, a little more elliptical in shape than most, and quite elderly (13 billion years old). It is also heading slowly in our direction, at 5.3 km/second. ‘Slowly’, of course, is relative to other intra-galactic speeds. Travelling at three miles a second would be plenty fast enough to get you a speeding ticket down here, but up there it’s nothing special.

(image from
(image from

Theoretically, M2 is a naked eye object if the sky is dark enough, but in practice that doesn’t apply round here in the land of the midnight security lamp. I need at least the small ‘scope to see anything.

Asteroid 125 Liberatrix, discovered by Prosper Henry (or possibly Paul Henry: you can never be sure) on September 11th 1872. It appears to be an M-type, and is possibly the biggest remnant of a larger body.

As for the name, the theory is that it honours Adolphe Thiers, president of the French Republic and suppressor of the Commune, who had recently been instrumental in extracting France from the Franco-Prussian War, in which they were doing none too well.

Asteroid 202 Chryseïs was discovered on this very day in 1879 by C F H Peters. It is about 86 km in diameter, and completes one full rotation every 16 hours as it travels at 17 km/second on its 5.4 year journey around the Sun.

Chryses visit to Agamemnon to ransom his daughter Chryseis (Image: Habib M’henni / Wikimedia Commons)
Chryses visit to Agamemnon to ransom his daughter Chryseis (Image: Habib M’henni / Wikimedia Commons)

In Greek mythology, Chryseïs (also known as Astynome) is indirectly the cause of most of the action in the Iliad. She is captured and enslaved by Agamemnon in Book One, and his refusal to allow her to be ransomed by her father, a priest of Apollo, eventually leads to all sorts of issues.

And while we’re talking of Apollo, asteroid 101955 Bennu was discovered on September 11th 1999 by the LINEAR project. It’s an Apollo, which means it has an orbit that brings it close to Earth, but in the case of Bennu not close enough to hit us (not yet, anyway). This proximity to Earth has led to Bennu being chosen as the target of the Osiris-REX “sample return” mission, which departed planet Earth in September 2016, and will return laden with souvenirs in 2023.

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