M80 - Globular Cluster in Scorpius


Discovered 1781 by Charles Messier.

Messier 80 (M80, NGC 6093) is a fine 8th mag globular. Its 10' angular diameter corresponds to roughly 95 light years linear dimension at its distance of 32,600 light years. Its appearance resembles very much that of a faint comet without tail.

This dense stellar swarm contains several 100,000's of stars, held together by their mutual gravitational attraction. It is one of the densest globulars in our Milky Way Galaxy. As was found by astronomers from observations with the Hubble Space Telescopein 1999 in the visible and UV part of the electromagnetic spectrum, M80 contains a large number of so-called "Blue Stragglers" in its core, about twice as much as any other globular investigated with the HST. These stars are blue and bright stars which appear near the main-sequence of the Hertzsprung-Russell diagramm, and thus appear more massive and younger than the globular clusters age. The reason is very probably that these stars lost their cooler envelopes in close encounters with other stars. Their large number in M80 indicates an exceptionally high stellar collision rate in the core of this globular cluster.

Globular cluster M80 was one of the original discoveries of Charles Messier, who found it on January 4, 1781, and cataloged it as a "Nebula without a star, .. resembling the nucleus of a comet." William Herschel was the first to resolve it (before 1785), and found it was "one of the richest and most compressed clusters of small stars I remember to have seen."

On May 21, 1860, a nova occurred in M80, completely changing the appearance of this globular cluster for some days. At its maximum, the nova was considerably brighter than the whole cluster !

M80, though not very conspicuous, can be located quite easily as it is situated almost exactly half-way between Antares (Alpha Scorpii) and Graffias (Beta Scorpii). It is seen as a bright but small, round ball with brighter nucleus; its surface brightness decreases to the outer regions. Messier determined a diameter of 2 arc min, but better moderate-sized amateur telescopes will show it as a mottled, nebulous object of size 3-5 arc mins, at best very poorly resolved. A better resolution into stars requires larger aperture telescopes.

Click on the image above to see it twice as large.

Imaging Details: 

Scope: Planewave 12.5" CDK
Camera: Apogee U16M w Astrodon Gen II LRGB filters
Mount: Paramount ME (MKS5000)
Guiding: SBIG ST-402ME and Astrodon MMOAG
RGB: 5/5/5 x 10min
Image acquisition via TSX and CCD-Commander
Calibration and initial combines in Maxim
Colour combine, Levels and Curves, Photoshop CS4

Lucknow, Ontario, Canada
May, 2015