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Starts With A Bang

Messier Monday: Messier’s first original discovery, M3

Image credit: © Mel Martin 2014, via

The handle of the Big Dipper leads you to Arcturus, the brightest star in the Northern Hemisphere. But there’s a deep-sky wonder hiding in plain sight, if you know where to look!

You look at most artists, the arc of their career, there’s a definite decline at the end. […] Time goes by fast, and you’ve got to be busy all the time.” –Seth

But in contrast to a human lifetime, there are fixtures in the night sky that won’t change perceptibly over many thousands (or even millions) of years! A great many of these help make up the Messier Catalogue, a collection of 110 prominent deep-sky objects that now serve as a fantastic set of objects to get yourself acquainted with the Universe!

Image credit: Tenho Tuomi of Tuomi Observatory, via

Tonight, a nearly full Moon will make many of the diffuse galaxies and nebulae invisible to most skygazers, but open star clusters and globular clusters still make for outstanding targets. For this week’s Messier Monday, let’s take a look at just the third object to be added to Messier’s catalogue: the globular cluster Messier 3. Here’s how to find it.

Image credit: me, created using the free software Stellarium, available at

The Big Dipper has begun to fly high overhead (for Northern Hemisphere observers) in the early part of the night, with its prominent cup and its arcing handle, ending in the blue star Alkaid. If you follow-and-extend the curve of the arc, you’ll come to the brilliant orange giant star, Arcturus, the brightest star in the northern celestial hemisphere. (The brightest overall, Sirius, is presently visible from the northern hemisphere, but is located well below the celestial equator.)

There’s a relatively dark patch of space between Alkaid and Arcturus, and that’s where Messier 3 can be found.

Image credit: me, created using the free software Stellarium, available at

Right next to Arcturus is its prominent neighbor, Muphrid. If you extend an imaginary line (not an arc!) from Muphrid back towards Alkaid, there will be three naked-eye stars — shown above with yellow arrows between them — than you can “hop” to: 6 Boötis, the somewhat fainter 3 Boötis, and culminating in the barely visible HIP 66725.

And if you can find that star in a low-magnification telescope or a pair of binoculars, you can’t miss Messier 3!

Image credit: me, created using the free software Stellarium, available at

It’s one of the most spectacular globular clusters in the entire night sky, and the very first object discovered by Messier that had never been mentioned or recorded before by anyone else. He recorded the following:

Nebula discovered between Bootes & one of the Hunting Dogs of Hevelius [Canes Venatici], it doesn’t contain any star, its center is brilliant, & its light is gradually fading away, it is round.

Through even a modest telescope, the sights are spectacular.

Image credit: © 1999-2013 Luís Carreira — Pátio da Astronomia, via

This sight — that looks like a snapshot of an explosion — is a familiar one to astronomers and avid skygazers: a globular cluster! Found around practically all known galaxies, these spherical collections of ~100,000 stars apiece live in the galactic halo, and are only rarely found in the disk. These are dense collections of stars, under 100 light-years in radius but much richer than our region of space. Our own galaxy contains more than 100 of these objects, but some galaxies contain tens of thousands. And Messier 3 is one of the most spectacular.

Image credit: © 2006 — 2012 by Siegfried Kohlert, of

Containing a rather abundant 500,000 estimated stars, Messier 3 has a very dense core about 6 light years in radius, and then spreads out, diffusely, for another 85 light-years or so. You’ll notice, looking at a color image of this galaxy, a large number of orange-red stars against a sea of yellow/white points, with just a few blue dots sprinkled in.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona, via

This is because globular clusters are among the oldest places in the Universe: the stars in Messier 3 are around 11.4 billion years old, and only contain about 4% of the heavy elements (Carbon, Oxygen, Iron, etc.) that our Sun has. However, most globular clusters are even older, forming within the first billion years after the Big Bang! It’s a relatively rare occurrence to have a globular cluster form later in a galaxy’s life; there must have been an incredibly large, intense period of star formation that created a star cluster so large that it still persists to this day.

Image credit: NOAO, in memory of Allan Sandage.

So that explains why there are bright orange-and-red stars there: those are Sun-like stars that have run out of their hydrogen fuel and have swelled into red giants. But what of the blue stars inside? Blue stars are shorter-lived and more massive than their white, yellow and red counterparts, and no blue star lives for 11 billion years or more. But remember, these are very dense regions of space, containing a much greater density of stars than our little corner of the Milky Way. When two stars collide and/or merge, their masses combine, and they can form what’s known as a blue straggler star, a common sight in globular clusters!

Image credit: Richard Steinberg of Drexel University, via

Some globulars have very dense cores and very diffuse outer halos, others are the opposite and don’t have a dense core at all! Messier 3 happens to be right in the middle: a VI on the concentration class scale, which ranges from I to XII. But while Messier 3 is unremarkable in this way, it’s remarkable in that — even at a distance of 34,000 light years — we’ve discovered more than 200 variable stars inside, more than we’ve found in any other globular cluster. We’re not entirely sure why this is the case, but look at ‘em go!

Image credit: Krzysztof Stanek and Andrew Szentgyorgyi, via Joel Hartman at

As always, the highest-resolution view of this objects comes courtesy of the Hubble Space Telescope, which has a narrow field-of-view. What you’re looking at, below, is a close-up of just the innermost 3 light-years or so.

Image credit: NASA / ESA / Hubble Space Telescope, via the Hubble Legacy Archive and Wikimedia Commons user FabianRRRR.

But why not carve a full-resolution slice through that, and give you a real view — at the limit of Hubble’s optics — at what’s inside!

Image credit: NASA / ESA / Hubble Space Telescope, via the Hubble Legacy Archive and Wikimedia Commons user FabianRRRR.

And with a spectacular view like that, that will bring us to the close of another Messier Monday. Previously, we’ve looked at the following Messier objects so far:

Travel the Universe with astrophysicist Ethan Siegel. Subscribers will get the newsletter every Saturday. All aboard!

Come back next week for another deep-sky wonder and another Messier Monday, and if you’ve got a favorite you can’t wait for, feel free to suggest it right here!


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