Because they consist of the oldest stars in a galaxy, globular clusters contain hydrogen and helium but virtually no heavier elements like carbon, oxygen, or iron, which are forged in supernova explosions after stars have formed. 47 Tucanae is unusual in that its stars show relatively high levels of heavier elements. This may mean it is young for a cluster, formed late in our galaxyΓÇÖs evolution, although much older than the Sun. In other respects 47 Tucanae is typical: with its round, highly concentrated clus- ter of stars, its structure is common among globular clusters. About 25 arc minutes across, 47 Tucanae is the closest globular cluster to Earth. Located in an otherwise empty portion of the Southern Hemisphere, it is visible to the naked eye.
