Capricornus
What is Capricornus?
Constellations· Late summer–autumn (N) · a triangle southeast of Altair. The sea-goat: a goat's head on a fish's tail. Smallest and faint among the zodiac signs, it earned a place in history as the spot where Neptune was first seen in 1846. Look for a blunt triangle of modest stars.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Capricornus is in your sky right now: https://nowsky.org/solar/sky?sel=con:Capricornus — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Deneb Algedi | 2.9 |
| Dabih | 3.1 |
| Algedi | 3.6 |
| Nashira | 3.7 |
The 4 brightest of the 8 stars used in the figure (8 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | late summer to autumn evenings, August–October |
|---|---|
| Brightest star | Deneb Algedi (2.9) |
| How to find | a blunt triangle southeast of Altair |
| Area rank | 40th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Capricornus?
- late summer to autumn evenings, August–October.
- How do I find Capricornus?
- a blunt triangle southeast of Altair.
- What is the brightest star in Capricornus?
- Deneb Algedi, magnitude 2.9.
- Where is Capricornus in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Two stars the eye can split — neighbours 600 light-years apart
Alpha Capricorni, Algedi, splits into two stars even to the naked eye: with good sight two stars six arcminutes apart appear side by side. They are not partners. The brighter, Algedi Secunda, lies about 100 light-years away and the fainter, Algedi Prima, about 700, some 600 light-years apart and merely placed in the same direction. Two stars that look closest to each other in the sky are in fact among the most distant of neighbours.
Such chance doubles could not be told from true binaries in the era before stellar distances were measurable. Only after parallax measurement began in the 1830s was it confirmed that neighbours in the sky and neighbours in space can differ, and Algedi became the easiest specimen of that difference. The pair at the goat's head is a place to see, with the eye alone, the depth hidden behind the sky's flat picture.
The constellation in depth
Capricornus has been drawn as a fish-tailed goat since Babylonian times. Greek storytellers made it Pan, who leapt into a river to escape the monster Typhon and turned only half into a fish, or Amalthea, the goat that suckled the infant Zeus. The winter solstice once lay here, hence the southern tropic's name, the Tropic of Capricorn. Ancient boundaries drifted, yet the sea-goat kept its odd hybrid shape through every star atlas since.
On 23 September 1846 Johann Galle at the Berlin Observatory, following Le Verrier's calculations, found Neptune near the star Delta Capricorni. It was the first planet located by mathematics before any telescope saw it. Algedi is a wide double that keen eyes can split unaided, and Dabih shows a companion in binoculars. The discovery vindicated Newtonian gravity so completely that Le Verrier was hailed as the man who found a planet with the point of his pen.
On late-summer evenings find Altair in the south, then drop southeast: a blunt triangle — some see a boat — of modest stars is the sea-goat. Without bright stars it is hard to trace from a city and rewards a dark sky. Set the Sky view to a September night to pick it out. Its stars lie between magnitude 3 and 4, so a moonless night away from town makes the difference between a blank patch and a recognisable outline.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.