An asterism composed of eight stars that runs through the central and western parts of Sagittarius and, as its name suggests, forms the shape of a Teapot complete with handle, lid and spout. The Teapot lies on the fringes of the Milky Way, directly northward of the prominent arc of Corona Australis, the Southern Crown, and eastward of bright red Antares in Scorpius.
The Teapot is largely composed from the stars of two smaller asterisms. Its handle and lid are formed from the five stars of the Milk Dipper, while the bow of Sagittarius runs down the western side of the Teapot from its lid. Together, these two asterisms account for seven of the eight stars of the Teapot. The eighth star, Alnasl, represents the end of the Teapot's westward-pointing spout.
The shape of the Teapot in the skies of Earth is purely a line-of-sight effect. The eight stars that make up the shape are actually quite unrelated to one other, and widely separated in space. They range from Kaus Borealis (marking the Teapot's 'lid') some 78 light years from Earth, to Kaus Media, appearing close to Kaus Borealis in the sky but actually more than four times farther from the Solar System.
The stars of the Teapot are generally second or third magnitude as seen from Earth, with the brightest being blue Kaus Australis with an apparent magnitude of +1.8. The faintest is the 'spout' star Alnasl, an orange giant nearly a hundred light years distant than shines with a visual magnitude of +3.6. With all eight stars being relatively bright, the formation stands out clearly in the heart of Sagittarius against the backdrop of the Milky Way.
These stars also vary widely in their natures, as revealed by spectral analysis. Four of the seven stars are orange giants, but Ascella is a white star, while Kaus Australis and Nunki both belong to the B-type blue spectral class (being a giant and a dwarf star, respectively).
Deep Sky Objects
The Teapot occupies an area in the general direction of the Milky Way's core, and so the eight stars that make it up lie against a rich backdrop. This is especially true of globular clusters, of which three important examples - M54, M69 and M70 - lie within the Teapot itself. Another two prominent clusters of the same kind - M22 and M28 - fall outside the Teapot shape itself, but nonetheless lie close to the 'lid' of the formation.
All of these globular clusters lie much farther across the Galactic disc than the stars of the Teapot, but of all of them, by far the most distant is M54. This cluster in fact lies within a dwarf galaxy lying on the opposite side of the Milky Way Galaxy from the Sun. This is a satellite galaxy of the Milky Way known as the Sagittarius Dwarf Galaxy, which is in the gradual process of coalescing with the main spiral. Much of its spheroidal form, though not visible to the naked eye, lies within the outline of the Teapot.