Reticulum
What is Reticulum?
Constellations· Southern summer · a small diamond beside the Large Magellanic Cloud. Reticulum is a small constellation named for the reticle, the crosshairs inside a telescope eyepiece. Four stars form a little diamond beside the Large Magellanic Cloud, and its best-known member is Zeta Reticuli, a pair of Sun-like stars.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Reticuli | 3.3 |
| Beta Reticuli | 3.8 |
The 2 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.
Constellation basics
| Season | Dec–Jan evenings; not visible from London or New York |
|---|---|
| Brightest star | α Reticuli, mag 3.3 |
| How to find | between the Large Magellanic Cloud and Achernar |
| Area rank | 82nd of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Reticulum II and the origin of cosmic gold
Where heavy elements such as gold and platinum were made in the universe was long an open question. One clue came from Reticulum. In 2015 a very faint small galaxy was discovered about 100,000 light-years away in this direction, and it was named Reticulum II.
When astronomers studied its stars, they found far more heavy elements such as gold and europium than in the stars of other small galaxies. In 2016 researchers explained this with a single event early in the galaxy's life: two neutron stars collided, and the heavy elements made in the crash spread through the whole galaxy.
The next year, in 2017, a collision of two neutron stars was actually caught through gravitational waves. Signs that heavy elements were made in that collision were observed too, supporting the explanation for Reticulum II. A faint galaxy in the direction of this small diamond constellation became a clue to where the universe's gold comes from.
The constellation in depth
Reticulum honours a tool Lacaille used to measure star positions from the Cape of Good Hope in the 1750s. Fine lines were set inside the telescope eyepiece, and he timed the moment each star crossed them to record its position precisely. These lines are called a reticle, which gives the constellation its name.
Reticulum is the seventh-smallest of the 88 constellations. Even so, its four stars make a neat little diamond that is easy to recognise. Before Lacaille, in the 1620s, another astronomer had already drawn a diamond-shaped figure in the same spot. Its brightest star, Alpha Reticuli, is a yellow giant of magnitude 3.3.
Zeta Reticuli is a pair of Sun-like stars about 39 light-years away, orbiting each other far apart. They are so widely separated that under a dark sky the naked eye can see two stars. Because they are Sun-like neighbours, they often come up in the search for life elsewhere. Around Epsilon Reticuli, a planet heavier than Jupiter has been confirmed.
Reticulum lies deep in the southern sky, so it cannot be seen from Europe or most of the United States. From the southern hemisphere, look on December and January evenings for the small diamond right beside the Large Magellanic Cloud. In the Sky view, set Cape Town or Sydney on a December evening and zoom in near the Cloud to see the diamond and the galaxy together.
Frequently asked
- When can I see Reticulum?
- Reticulum is best seen in Dec–Jan evenings; not visible from London or New York.
- How do I find Reticulum?
- To find Reticulum, look for between the Large Magellanic Cloud and Achernar.
- What is the brightest star in Reticulum?
- The brightest star in Reticulum is Alpha Reticuli, at magnitude 3.3.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.