Beautiful M5 Globular Cluster Will Send Shivers Down Your Spine

One of the most spectacular globular clusters in the entire sky, M5 is easy to spot in binoculars north of the star Beta Libra near the planet Saturn this spring. It contains up to 500,000 stars and is located 25,000 light years away in the outer halo of the Milky Way. Credit: Jim Misti

“The night of May 23 to 24, 1764, I have discovered a beautiful nebula in the constellation of Serpens, near the star of sixth magnitude,” wrote 18th century French astronomer Charles Messier. He was sooooo right! About the beauty part that is.

The “nebula” seen by Messier would become the 5th entry in his catalog of 110 fuzzy deep sky objects masquerading as comets, his preferred prey. Of course M5 is no nebula. Messier’s telescope was too small to reveal its true character as a densely-packed cluster containing up to half a million stars and as massive as 800,000 suns. We know it as one of some 150 globular clusters that dot the Milky Way’s spherical halo.

M5 sits about a dozen degrees – a little more than a fist held at arm’s length – above the planet Saturn in the constellation Serpens the Serpent. To find it in binoculars, place Beta Librae right of center in your field of view and tilt the binoculars upward up until you arrive at a blurry spot with a bright center paired with the magnitude 6 star 5 Serpentis. The map shows the sky around 10:30 p.m. local time. Stellarium

Small telescopes in the 4-6 inch range will reveal a fuzzy, slightly elliptical ball with tiny sprinkles of stars visible around its edges. Prepare to spend many minutes basking in its beauty if you have an 8-inch or larger telescope at hand. Hundreds of stars appear to swirl out from a central core that glitters like a swarm of fireflies or snow sparkling in sunlight. The vagaries of vision and atmospheric seeing make the cluster’s dimmer stars appear to flicker or sparkle, further enhancing the ‘firefly effect’.

The Great Globular M13 in Hercules usually gets more ‘likes’ than any cluster of this class, but I give my vote to M5. The cluster core is packed a little more tightly and the outlying starry whorls impart a sense of motion to the view like a spinning pinwheel.

When observing globulars, it’s important to use medium magnification (x100-150) to more clearly resolve the stars while not going so high they take on a mushy appearance. On rare nights when atmospheric turbulence doesn’t interfere, the clarity, crispness and vast number of stars visible make M5 one of the most moving sights in the heavens. Second only to Saturn I swear.

Profile of the Milky Way galaxy shows its main parts: the central bulge of stars, the disk of stars and gas and a large spherical halo populated by globular clusters. The sun is located a little more than halfway from center to edge, and the galaxy spans about 100,000 light years. Credit: Durham University

M5 measures 165 light years across or a little more than the distance between Earth and V-shaped Hyades Star Cluster that outlines the face of Taurus the Bull. With its hundreds of thousands of suns, a planet orbiting a star in M5 would see a sky scintillating with dozens of Venus-bright luminaries.

Closeup of the inner 20 light years of M5 taken with the Hubble Space Telescope shows many of the bright red and blue giant stars that light up the cluster. Credit: NASA/ESA

Globulars are densely packed balls of stars held together by mutual gravitational attraction. That’s what gives them their spherical shapes. They formed about the same time the Milky Way galaxy took shape and have ages measured in the billions of years. It used to be thought that M5 was one of the very oldest with an age of 13 billion years (remember, the universe itself snapped into existence 13.8 billion years ago). A more recent 1997 study pegs it closer to 10.6 billion. Hey, that’s still darn ancient!

The Andromeda Galaxy hosts about 500 globulars while the giant elliptical galaxy M87 in Virgo contains 13,000 of them cycling around its inner core. Amazing, profligate nature.

All those little dots that look like stars are globular clusters orbiting the core of the galaxy M87 in Virgo. Credit: NASA/ESA

All the sun-sized stars that once populated globulars have since evolved into giant stars. The combined light of so many giants is one reason we can see globulars across enormous distances. M5 shines at magnitude +5.7 and visible with the naked eye from a dark sky location. I’ve spotted it from Duluth a few times, but it’s not easy because the cluster’s somewhat low in the southern sky.

Binoculars show it very plainly as a small, soft blob of light next to 5 Serpentis. Take a look the next clear night. Telescopic observers, be prepared to be wowed!

5 Responses

  1. Larry D

    No question that globular clusters are the most beautiful. It seems that everything gets quieter when you have one centered in the eyepiece.

  2. Kevin Heider

    Still wonder if a prefer M5 or M3 (which is even closer to Arcturus). M92 in Hercules is often overlooked because everyone looks at M13 so much.

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