Sagitta

Sagitta (the Arrow) is one of the three smallest constellations, after Equuleus and Crux. It is located within the perimeter of the Summer Triangle, the great asterism formed by Deneb (α Cygni), Vega (α Lyrae) and Altair (α Aquilae).

Notable features

Sagitta constellation

γ Sagittae, a red giant of spectral type M0III, is the brightest star in Sagitta. Large in size, it has a radius 55 times larger than the solar radius. Next in brightness is δ Sagittae, also a red giant although cataloged as M2II, it is a luminous giant 2800 times more luminous than the Sun and four times more luminous than γ Sagittae. It is also a spectroscopic binary, its companion being a hot B9.5V type star. The third brightest star is α Sagittae, known as Sham. It is also a luminous giant, but of spectral type G1II.

Another star in the constellation, 15 Sagittae, is a yellow dwarf of spectral type G0V similar to the Sun. It lies 58 light-years away and appears to be younger than our star. It is physically linked to a brown dwarf that takes 73.3 years to complete one orbit around it.

U Sagittae is an eclipsing binary composed of a blue-white star of spectral type B8V, the primary component, and a yellow giant of type G2III-IV, the secondary component. Its orbital period is 3.3806 days, with the practically circular orbit (ε = 0.03). Another variable to highlight is FG Sagittae, a supergiant found in the center of the planetary nebula Hen 1-5. It has evolved significantly in recent years, changing its spectral type from B4Ia in 1955 to A5Ia in 1967, to F6Ia in 1972, and is currently an orange star of spectral type K2Ib. Since the 1990s it has behaved as an R Coronae Borealis variable, with partial dimming and recoveries caused by dust obscuring the star. Also of interest is WZ Sagittae, prototype of a subclass of cataclysmic variables that bears his name. Its last outbreak took place in 2001, but others had previously been recorded in 1913, 1946 and 1978.

WR124, known as Merrill's Star or QR Sagittae, is a Wolf-Rayet star of spectral type WN8h and 44,700 K of temperature. Considering that it is at an estimated distance of 6,400 parsecs, its luminosity is 575,000 times greater than that of the Sun. It is surrounded by clumps of incandescent gas that form the surrounding M1-67 nebula.

The globular cluster M71 is located in Sagitta, 13,000 light-years from Earth. It was discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier in his object catalog in 1780. The variable Mira Z Sagittae is a member of this cluster.

On the other hand, SNR G054.1+00.3 is a supernova remnant in this constellation; Its supernova explosion is believed to have taken place 2,000 - 3,000 years ago and left the pulsar PSR J1930+1852 as a stellar remnant.

Main Stars

Image of the M1-67 nebula that surrounds WR 124, obtained with the Hubble space telescope.

• α Sagittae (Sham), although it holds the Bayer denomination Alpha, it is only the third brightest star of the constellation with magnitude 4.37. It's a yellow giant at 475 light years away.
• β Sagittae, yellow giant of magnitude 4,39.
• γ Sagittae, the brightest in Sagita has magnitude 3,47; it is a red giant located at 275 light years.
• δ Sagittae, spectroscopic binary composed of a red giant and a white star.
• ε Sagittae, yellow-orange giant of magnitude 5.67.
• ج Sagittae, multiple star of magnitude 5,00.
• Cristian Sagittae, orange giant of magnitude 5,10.
• 13 Sagittae (VZ Sagittae), a red and irregular variable giant whose brightness varies between magnitude 5.27 and 5.57.
• 15 Sagittae, with magnitude 5.8 is a binary star formed by a yellow dwarf similar to the Sun and a brown dwarf.
• S Sagittae (10 Sagittae), a shaved variable whose brightness ranges from 5,24 to 6.04 with a period of 8,382 days.
• U Sagittae, an interesting eclipse variable composed of a blue star and another orange, whose magnitude ranges from 6.5 to 9.3 in more than three days and nine hours.
• FG Sagittae, star of a planetary nebula whose color and temperature has been changing over the last 100 years.
• HD 178428, spectrum binary of magnitude 6.07.
• HD 183143, hypergigante star with an apparent magnitude of 6.86.
• HD 231701 (Uruk), white-yellow star with an extrasolar planet.
• WR 124, star of Wolf-Rayet surrounded by the M1-67 nebula.
• Gliese 745, a system composed of two red subenanas of the thick disk.

Deep Sky Objects

Image of the M71 cluster obtained from the Calar Alto Observatory.

• M71 globular cluster, located close enough to Earth to distinguish its giant red stars with any telescope. Its apparent dimensions are like a fifth of the diameter of the full moon.
• 3C 400.2, remainder of old supernova whose age can be 45 000 years.
• SNR G054.1+00.3, also a remainder of supernova, but much younger (between 1500 and 3600 years).

Mythology

The ancient Hebrews, Persians, Arabs, Greeks and Romans already considered this group of stars to be an arrow.

According to Eratosthenes, it was the arrow that Apollo used to kill the Cyclopes, in revenge for the fact that his son Asclepius had been struck down. Apollo then hid the arrow in the country of the Hyperboreans and retrieved it once Zeus had forgiven this act once Apollo had served King Admetus of Pheras.