How Many Stars Are in Hercules?
Hercules is the fifth-largest constellation — and one of the emptiest-looking. It has just two stars brighter than magnitude 3, and the shape you actually recognise is a square of four: the Keystone. Yet hidden on that square’s edge is a single dim smudge holding about 300,000 stars.
The Keystone emerges — a lopsided square that forms the hero's torso, the key to finding everything else.
Tap the four ringed Keystone stars, or the glowing M13 — that one isn’t a star.
So how many stars are in Hercules — really?
Here’s the paradox. Hercules sprawls across 1,225 square degrees — only four constellations are bigger — but it’s the largest of all the constellations that contain no star brighter than magnitude +2.5. Stand under a suburban sky and you might struggle to find it at all. To the naked eye, the honest count is modest: the four stars of the Keystone, the brighter Kornephoros and Rasalgethi nearby, and a scattering of fainter stars marking the arms and legs — perhaps a dozen you can comfortably trace. Yet inside that same outline sits M13, a cluster that looks like one faint, fuzzy star but is really a swarm of around 300,000. So the "how many" answer flips depending on where you point: a dozen stars to draw the hero, or hundreds of thousands in a single dot on his hip. Drag the slider on the map, then tap M13.
The Keystone: four stars that anchor the hero
Because Hercules has no bright beacon, the way in is the Keystone — a lopsided square of four stars (Eta, Zeta, Epsilon and Pi Herculis) that represents the kneeling hero’s torso. Find it halfway along an imaginary line between brilliant Vega and orange Arcturus, and the rest of the faint figure unfolds around it. Here are the brightest named stars in the constellation:
| Star | Part of the figure | Magnitude | Distance |
|---|---|---|---|
| Kornephoros (β Her) | Shoulder · brightest | 2.81 | ~139 ly |
| Zeta Her (ζ Her) | Keystone | 2.81 | ~35 ly |
| Sarin (δ Her) | Shoulder | 3.12 | ~75 ly |
| Pi Her (π Her) | Keystone | 3.16 | ~370 ly |
| Eta Her (η Her) | Keystone | 3.48 | ~112 ly |
| Rasalgethi (α Her) | Head | 3.5 | ~360 ly |
| Epsilon Her (ε Her) | Keystone | 3.92 | ~155 ly |
| Maasym (λ Her) | Arm | 4.4 | ~370 ly |
Note the oddity: Kornephoros (β) outshines Rasalgethi (α). The "alpha" star is a variable that usually sits fainter.
M13: three hundred thousand stars in a single smudge
The real reason stargazers love Hercules hangs on the western edge of the Keystone, between Eta and Zeta. Messier 13, the Great Globular Cluster, is the finest globular in the northern sky: a tightly bound ball of roughly 300,000 stars, about 145 light-years across, some 25,000 light-years away. At magnitude 5.8 it’s just visible to the naked eye under a perfectly dark sky as a hazy point — and through a telescope it explodes into thousands of resolvable pinpoints. Edmond Halley discovered it in 1714, and in 1974 humanity beamed its first deliberate interstellar message, the Arecibo message, in M13’s direction. A short distance north lies a second globular, M92 — overlooked only because it shares the sky with its famous neighbour.
Rasalgethi: the giant at the kneeler’s head
The star marked alpha, Rasalgethi — "the kneeler’s head" — is a monster. It’s a red giant roughly 400 times the width of the Sun; drop it where the Sun sits and its surface would reach beyond the orbit of Mars. It pulses as an irregular variable between about magnitude 2.7 and 4.0, which is why it loses the "brightest star" title to Kornephoros most nights. Through a telescope it’s also a lovely double, the giant glowing orange beside a smaller blue-green companion — one of the prettiest contrasting pairs in the sky.
How to find Hercules tonight
Hercules is a summer constellation in the Northern Hemisphere, riding highest in the evening through July and August, and visible across most of the world. Don’t look for a bright pattern — look for the Keystone. The quickest route: find dazzling Vega and orange Arcturus, two of the brightest summer stars, and the Keystone sits roughly between them. You can also extend the straight part of the Big Dipper’s handle until it reaches a faint square. Once you’ve got the Keystone, scan its western edge with binoculars and M13 will reveal itself as a glowing cotton ball.
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The faintest corner held our return address
It’s a strange thing that the dimmest-looking large constellation in the sky hides the most crowded object most of us will ever see. The entire dome of the night holds about 9,000 stars visible to the naked eye. M13 — one unremarkable smudge you’d walk straight past — packs more than thirty times that number into a space you could cover with a fingernail at arm’s length.
In 1974 we pointed the giant Arecibo dish at exactly that smudge and sent a message — a little diagram of who and where we are — toward those 300,000 suns, on the reasoning that the more stars you aim at, the better your odds of someone listening. It won’t arrive for 25,000 years. By the time it does, the Keystone will have drifted, the message long forgotten on Earth, still travelling toward a cluster older than the Sun.
So how many stars are in Hercules? Barely a dozen you can name — and three hundred thousand you can hide behind your thumb.
Sources
- Wikipedia & NOIRLab, Hercules — the constellation’s size and faintness, the Keystone, and M13’s ~300,000 stars.
- Constellation-Guide & freestarcharts — the named stars, per-star magnitudes and distances, and the Keystone’s four stars.
- EarthSky, Hercules the Strongman — how to find it between Vega and Arcturus, and the M13 / M92 globulars.
- M13 distance, diameter, age and the 1974 Arecibo message from the same astronomical references.