Tucana
What is Tucana?
Constellations· Southern spring evenings · not visible from mid-northern latitudes · home of the SMC. Tucana depicts the toucan, a bird of South America. Its stars are faint, but it holds the Small Magellanic Cloud, a small galaxy that orbits ours, and the bright globular cluster 47 Tucanae. It cannot be seen from Europe or most of North America.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Tucanae | 2.9 |
| Gamma Tucanae | 4.2 |
The 2 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.
Constellation basics
| Season | southern spring evenings · not visible from London or New York |
|---|---|
| Brightest star | Alpha Tucanae (2.9) |
| How to find | south of Achernar, around the SMC |
| Area rank | 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The fast-spinning pulsars inside 47 Tucanae
47 Tucanae is a globular cluster with millions of stars packed into a small space. When stars are this crowded, they often pass close to one another and swap partners. As a result, 35 millisecond pulsars, which spin hundreds of times per second, have been found in this cluster. That is the second-largest number known in any globular cluster.
A pulsar is a neutron star, the tiny and very dense core left behind when a big star dies. It sends out radio pulses as regularly as a lighthouse beam. When it pulls material from a companion star, it spins faster and faster, and that is how millisecond pulsars form. Their signals keep time like precise clocks, so small changes in when the pulses arrive show how mass is spread inside the cluster.
Astronomers have also used this method to ask whether a medium-sized black hole sits at the cluster's centre. A 2017 study claimed one, but a later analysis with more data found no solid evidence. So the question is still open. The cluster is about 15,000 light-years away, some thirteen times closer than the Small Magellanic Cloud behind it.
The constellation in depth
Tucana is one of the southern constellations Petrus Plancius created in 1598 from the observations of Dutch navigators. It honours an unfamiliar bird that sailors saw on their voyages, and some early charts called it the Indian Magpie. Its stars lie close to the south celestial pole, so they had never been seen from Europe before.
Its brightest star is only magnitude 2.9, so the figure itself is hard to spot. What it does contain is the Small Magellanic Cloud. This is a small galaxy about 200,000 light-years away that orbits the Milky Way. Under a dark sky it is visible to the naked eye as a small cloud that seems to have broken off the Milky Way. The name comes from the voyage of the explorer Ferdinand Magellan.
Right beside the Small Magellanic Cloud lies the globular cluster 47 Tucanae (NGC 104). A globular cluster is a huge ball of tightly packed stars. This one is the second-brightest in the sky after Omega Centauri, and to the naked eye it looks like a slightly fuzzy star. The two seem to touch in the sky, but the cluster is inside our own galaxy and much closer.
Tucana lies near the south celestial pole, so it never rises from Europe or most of the United States. From the southern hemisphere it rides high in the south on evenings from September to December. Set the Sky view location to Sydney or Cape Town, and Tucana and the Small Magellanic Cloud appear together below the bright star Achernar.
Frequently asked
- When can I see Tucana?
- Tucana is best seen in southern spring evenings · not visible from London or New York.
- How do I find Tucana?
- To find Tucana, look for south of Achernar, around the SMC.
- What is the brightest star in Tucana?
- The brightest star in Tucana is Alpha Tucanae, at magnitude 2.9.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.