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Object of the Week April 9, 2023 – Messier 3
Messier 3, NGC 5272
Constellation: Canes Venatici
Type: Globular Cluster
RA: 13h 43m 16s
DEC: +28° 15’ 38”
Mag(v): 6.2
Size: 18’
NGC 5272, also known as Messier 3, is a globular cluster located in the constellation Canes Venatici. It was first discovered by French astronomer Charles Messier on May 3, 1764. Messier initially cataloged the object as a nebula, but later observations by William Herschel in the late 18th century revealed it to be a globular cluster.
When Charles Messier first noticed this object – on May 3rd, 1764 – it was only the 76th Deep Sky Object ever seen by human eyes (with the assistance of telescopes, that is). Although Charles had logged his previous two discoveries (the M1 "Crab Nebula" and the globular cluster M2) it was this third object that prompted him to begin his now famous catalog of 'objects that are not comets'.
As Messier recorded at the time in in his notes: "On May 3, 1764, when working on a catalog of the nebulae, I have discovered one between Bootes and one of the Hunting Dogs [Canes Venatici] of Hevelius, the southernmore of the two, exactly between the tail and the paws of this Dog, according to the charts of Flamsteed. I have observed that nebula on the meridian, and I compared with Mu Bootis; its right ascension has been found as 202d 51? 19?, and its declination as 29d 32? 57? north. That nebula which I have examined with a Gregorian telescope of 30 pouces focal length, which magnifies 104 times, doesn't contain any star; the center is brilliant, and the light gets lost fading [outward]; it is round, and could have 3 minutes of arc in diameter. One can see it in a good sky with an ordinary [non-achromatic] refractor of one foot [FL] , it doesn't contain any star, its center is brilliant, and its light is gradually fading away, it is round; in a beautiful [dark] sky."
As with other objects recorded by Messier, it was Sir William Herschel who first resolved the M3 into stars. As he recorded in his own observational notes: "To these may added the 1st, 3d [M3], 27, 33, 57, 79, 81, 82, 101 [of Messier's catalog], which in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed…"
But none described it more eloquently than Admiral William Henry Smyth – an English astronomer and naval officer. As he wrote: "A brilliant and beautiful globular congregation of not less than 1000 small stars, between the southern Hound and the knee of Bootes; it blazes splendidly towards the centre, and has outliers in all directions, except the sf [south following; SE], where it is so compressed that, with its stragglers, it has something of the figure of the luminous oceanic creature called Medusa pellucens. This noble object is situated in a triangle formed by three small stars in the np [north preceding; NW], nf [north following; NE], and sf [south following, SE] quadrabts, which, by their comparative brightness, add to the beauty of the field. It is nearly in mid-distance between the Arcturus star and Cor Caroli, at 11deg north-west of the former star. This mass is one of those balls of compact and wedged stars, whose laws of aggregation it is so impossible to assign; but the rotundity of figure gives full indication of some general attractive bond of union."
Here are some additional facts about NGC 5272:
- In 1893, American astronomer Edward Charles Pickering was the first to discover variable stars in the cluster, specifically RR Lyrae stars. Pickering's discovery of these stars in NGC 5272 marked the beginning of the study of variable stars in globular clusters, which has since become an important area of research in astronomy.
- M3 is a very active cluster, with a number of different types of variable stars. Identification of the cluster's unusually large variable star population was begun in 1913 by American astronomer Solon Irving Bailey and new variable members continue to be identified up through 2004. It contains 274 known variable stars, by far the most found in any globular cluster. These include 133 RR Lyrae variables.
- In the early 20th century, astronomers continued to study NGC 5272 and other globular clusters in detail, using techniques such as photometry and spectroscopy to measure the properties of the stars within the cluster. One notable study was conducted by Danish astronomer Ejnar Hertzsprung in the 1920s, who used photometry to measure the distances to several globular clusters, including NGC 5272. Hertzsprung's work helped to establish globular clusters as important tools for measuring distances in the universe.
- The stars in M3 are very old, with an estimated age of 11.4 billion years. They are also very metal-poor (low metallicity, population II stars), meaning that they have very low levels of the heavy elements, i.e., all elements other than hydrogen and helium. This is consistent with the idea that globular clusters formed very early in the history of the Milky Way, when the galaxy was still relatively metal-poor.
- The cluster contains primarily old, red stars. But it also contains a relatively large number of so-called "Blue Stragglers", blue main-sequence stars which appear to be much younger than the rest of the globular's stellar population. Once puzzling to astronomers, these stars are now thought to form as a result of stellar interactions; their cooler outer layers are stripped away in close encounters, which occur when they pass through the dense central regions of the cluster.
- It is one of the most massive globular clusters in the Milky Way, with a mass of about 500,000 suns.
- It is one of the most luminous globular clusters in the Milky Way, with a luminosity of about 100,000 suns.
Many consider Messier 3 to be one of the finest northern globular clusters, following only Messier 13. In binoculars of all sizes and even under urban lighting conditions, M3 is bright and will begin to show some signs of resolution with higher power objectives, such as 10X50. Telescopes as small as 6? will begin to show individual stars come to life and explode into a fine, pinpoint mass.
To further whet your appetite for this beautiful globular cluster, here is a sampling of others observational reports.
- Burham’s Celestial Handbook Burnham calls it a "superb object", describing it as a "beautiful bright globular cluster, one of the most splendid in the sky. It was discovered by Messier in 1764 and can be seen as a hazy 6th magnitude 'star' in field glasses. The small telescope shows it as a round nebulous object about 10' in diameter ... at least a four-inch telescope is needed to partially resolve the outer edges, and a good 6-inch glass with a fairly high power will reveal hundreds of stellar points. Large telescopes show an incredible swarm of countless star images, massing to a wonderful central blaze, with glittering streams of stars running out on all sides. The seeming arrangement of the outer members into radiating streams and branches was noticed by both the Herschels and Lord Rosse [Admiral Smythe mentions the strings of stars at the outer edge of the cluster. He also notes that the cluster has a curious resemblance to a jellyfish.] ... Lord Rosse found several small dark obscuring patches in the central mass, more or less verified on modern photographs [some of which appear on photographs taken with the 120" reflector at Lick Observatory], but more definitely present in the Hercules system M13. ... M3 contains many thousands of stars, from magnitude 11 or so to the limit of detectability. ... At Palomar Observatory, more than 45,000 stars have been counted in this cluster, down to magnitude 22.5."
- Walter Scott Houston Houston notes: "In a 10-inch, its edges break down into glittering stars, some of which may show even in the bright central blaze. Unlike M13 in Hercules, M3 does not seem to have strings of stars trailing outward."
- Magda Streicher 12-inch f/10 SCT (95x/52.8?, 218x/23.1?)
Like all globular clusters there is something unique to them. M3 displays a very dense core more or less 1' in size, which is on the verge of resolving into starlight. However from this compact, bright-unresolved core, starlight became visible and multiplies along to the edges. It blazes off with outliers and pinpoint stars scattered around the flimsy edges of the cluster. The southwestern side of the globular is busier with star strings that spray out into the field of view. A triple star on the south east of the globular keeps coming back into my eye's view.
- The Night Sky Observer’s Guide Volume II
4/6" Scopes-100x: This globular is a fine sight in small telescopes! It is bright, large, and round with a rich granular halo growing smoothly brighter to a small brilliant core.
8/10" Scopes-100x: Messier 3 is a beautiful globular cluster that rivals Messier 13 in Hercules. It has a very bright, large core spanning half of the 10' diameter halo which thins gradually to a loose periphery of outlying stars. The halo is well resolved nearly to the cluster's center.
12/14 " Scopes-125x: Superb! Messier 3 is a glittering ball of stars with an extremely bright, rich, oval core elongated 5' × 4' NW-SE and surrounded by a 16 diameter halo of pinpoint stars. The stars are well resolved even across the core, and radiate outward from it in curved chains.
Attachment 5096
Credits: NASA, ESA, STScI and A. Sarajedini (University of Florida)
As always, give it a go and let us know.
