<body><div>Messier 13 (M13) is truly a beautiful globular star cluster in the Constellation Hercules was taken with an SBIG STL-11000M CCD and a RCOS 24-inch telescope at the Mount Lemmon SkyCenter.Messier 13 is truly a stand alone globular star cluster and is often referred to as (M13) was discovered in the year 1714 by Edmond Halley and was cataloged on June 1, 1764 by Charles Messier into his list of objects not to mistake for comets. Messier's list which included Messier 13 (M13), eventually became known as the Messier catalog. It is located at right ascension (R.A.) 16h 41.7m, declination (Dec.) +36° 28'. Messier 13 (M13) is often described by astronomers as the most magnificent globular cluster visible to observers in the northern hemisphere.At a distance of about a third of the way from the star Vega to Arcturus, there are four bright stars in the constellation Hercules that form the well known Keystone asterism, known as the broad torso of the hero Hercules. Messier 13 (M13) can be seen in this asterism 66% of the way north (by west) from Zeta to Eta Herculis. With an apparent magnitude of 5.8, Messier 13 (M13) may be visible to the naked eye using averted vision on dark nights. Messier 13 (M13) is quite prominent in ordinary 7x50 binoculars as a bright, round patch of modulated light. Its stellar diameter is approximately 23 arcminutes and it is easily viewable in the smaller telescopes. Telescopes with at least four inches of aperture can resolve stars in Messier 13's (M13) outer extent as rather small pinpoints of light. However, only the larger telescopes with greater aperatures can resolve stars further into the center of the Messier 13 (M13) cluster. The Messier 13 (M13) cluster is normally visible throughout the entire calendar year from greater latitudes (greater than 36 degrees north), with the longest visibility during Northern Hemisphere spring and summer periods.Somewhat close to Messier 13 is NGC 6207, which is an impressive 12th-magnitude edge-on galaxy that lies approximately 28 arcminutes directly northeast of Messier 13 (M13). There is a small galaxy, IC 4617, that lies halfway between NGC 6207 and Messier 13 (M13) and is located north-northeast of the large globular cluster's galactic center. Observing using low powers the cluster is viewed bracketed by two seventh–magnitude stars. Messier 13 (M13) is about 145 light-years (One light year equals 6 trillion miles) in it’s overall globular cluster diameter and is composed of several hundred thousand stars, with estimates varying from around 300,000 to over half a million and more. The brightest star in the cluster is a red giant, the variable star V11, also known as V1554 Herculis, with an apparent visual magnitude of 11.95. Messier 13 (M13) has a distance that is 22,200–25,000 light-years away from Earth, and the Messier 13 (M13) globular cluster is one of over one hundred that are known to orbit the central region of the Milky Way.The stars in this cluster are firmly embedded in the Population II category, which is somewhat lower in metals department than Population I stars like the Sun and majority of the other stars in the Sun's close proximity. Messier 13 (M13) as a whole has only about 4.6% or even less as much iron as the Sun does.Stars of the singular variety in this globular cluster were first resolved in 1779. Compared to the stars in the neighborhood of the Sun, the stars of the Messier 13 (M13) globular cluster population is quite densely packed and are somewhat close together that they sometimes collide with each other and produce some new stars. These new recently formed young stars which are commonly known as the "blue stragglers" are of particular interest to astronomers. It’s interesting to note that the last three variables (V63, V64 and V65) were discovered from an observatory in Spain in April 2021, March 2022 and January 2024.My humble 3.55-inch f/7.8 Chinese refractor pictured above which I bought on the island of Saipan a few years ago can resolve Messier 13 make for a night’s fine observing not only for globular clusters like Messier 13…but also faint galaxies and nebula too.</div></body>

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Messier 13

Messier 13 (M13) is truly a beautiful globular star cluster in the Constellation Hercules was taken with an SBIG STL-11000M CCD and a RCOS 24-inch telescope at the Mount Lemmon SkyCenter. Messier 13 is truly a stand alone globular star cluster and is often referred to as (M13) was discovered...

Messier 13

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