Stars
Alcor
(Alcor or 80 Ursae Majoris) With normal eyesight one can make out a faint companion just to the east. Alcor is of magnitude 3.99 and spectral class A5V.
Mira
(Omicron Ceti) Located in the constellation Cetus is a red giant 200-400 LY from Earth. Mira is a binary star system. Mira A and Mira B make up this star system. Mira A is an oscillating variable star and the first non-supernova variable star dicovered.
Altair
(α Aquilae)- The 12th brightest star in the sky with an apparent magnitude of 0.77, Altair is one of the vertices of the Summer Triangle (along with Vega and Deneb). It is flattened at the poles due to its high rotation speed. The name Altair comes from a shortened version of the Arabic phrase "the flying eagle". Altair is a A7V star and it's 16.8 LY away.
Capella
(α Aurigae)- Part of the Hyades moving group, Capella is the 6th brightest star in the night sky and the 3rd brightest in the northern celestial hemisphere. It is actually a "star system" of 4 stars in 2 pairs. The first pair are G8III and K0III stars (probably previously A-class stars that have now moved off the main sequence and are becoming red giants) while the second pair consists of 2 small, cool, dim red dwarfs. Combined, these stars have an apparent magnitude of 0.08; additionally, they are 42.2 LY from Earth. There are lots of x-rays being emitted from the corona of the largest star. Capella means "she-goat.
Arcturus
(α Bootïs)- With an apparent magnitude of -0.05 (can vary by 0.04), Arcturus is the fourth brightest star in the nighttime sky. However, it is less bright than Alpha Centauri A and B combined, which means that it is the third brightest individual star in the night sky. Arcturus might actually be a binary star with a companion around 20 times or so dimmer, at the very edge of our ability to detect it. Arcturus is about 36.7 LY away and is a K1.5III star. The name is derived from Arabic for "bear guard", because it is close to both Ursa Major and Ursa Minor.
Sirius
(α Canis Majoris, the "Dog Star")- Sirius is the brightest star in the night sky, with an apparent magnitude of -1.47. The binary star system consists of Sirius A (an A1V star) and Sirius B (which used to be even larger than Sirius A but has evolved into a white dwarf). Sirius can be seen up to 73 degrees north or south of the equator, and it's one of the vertices of the Winter Triangle, along with Procyon and Betelgeuse. The nickname "Dog Star" comes from the constellation Sirius is in: Canis Major, the Big Dog. Sirius is about 8.6 LY away.
Procyon
(α Canis Minoris)- Procyon is the 7th brightest star in the nighttime sky with an apparent magnitude of 0.34. Procyon is a binary star system (Procyon A is a F5IV-V star, Procyon B is a white dwarf) and it's also a vertex of the Winter Triangle. Procyon forms a prominent equilateral triangle with Sirius and Betelgeuse. In Greek, Procyon means "preceeding the dog", because it rises before Sirius.
Proxima Centauri
(α Centauri C)- Proxima Centauri is the closest star to our sun. Proxima means nearest. Being an 11th-magnitude star and is only visible in a telescope. It is part of the Centauri system.
Deneb
(α Cygni)- One of the vertices of the Summer Triangle, Deneb is an A2I star about 1550 LY away. With an apparent magnitude of 1.25, Deneb is actually the farthest 1st-magnitude star from Earth. It will probably become a supernova in a few million years. Because Deneb is the tail of Cygnus, the swan, its Arabic name is quite fittingly, "tail".
Castor
(α Geminorum)- Castor is the second brightest star in the constellation Gemini, named after one of the twin sons of the Greek god Zeus. Castor is actually a sextuple star system, with two pairs of A-class stars (1V and 2V) and M-class stars orbited by two more M-class dwarfs. The apparent magnitude can be either 1.96 or 2.91, depending on which of the A-class stars is measured.
Regulus
(α Leonis)- Around 77.5 LY away, Regulus is a quadruple star system- Regulus A is a B7V star with a white dwarf companion, while Regulus B and C are dim main sequence stars (a K1-2V star and a M5V star, respectively). Regulus A is a young star that spins very rapidly and it has a magnitude of 1.35. The name comes from Latin for "little king" or "prince".
Vega
(α Lyrae)- Vega is the 5th brightest star in the night sky and the 2nd brightest in the northern celestial hemisphere. It is an A0V star approximately 25 LY away that is flattened at the poles due to its high rotation speed. Vega is 1/10 the age of the Sun, but it's already halfway through its life as a main sequence star. There is the possibility that Vega has its own little solar system of sorts- it may have orbiting planets. Vega is a vertex of the Summer Triangle (the other vertices are Altair and Deneb). The name is derived from the Arabic phrases for either "falling eagle" or "swooping vulture".
Betelgeuse
(α Orionis)- Betelgeuse (yes, pronounced beetle-juice) is a M2I red supergiant about 600 LY away. It is most likely a young star evolving quite rapidly. Betelgeuse is usually the second brightest star in Orion with an apparent magnitude of around 0.58, but since it's a variable star, Betelgeuse is sometimes brighter than Rigel. Also, it is one of the vertices of the Winter Triangle, along with Sirius and Procyon. "Betelgeuse" comes from a mistranslation of the Arabic phrase for "hand of the central one". Betelgeuse is considered very likely to go supernova after its red giant phase.
Antares
(α Scorpii)- Antares is a M1.51 star (a supergiant), with an apparent magnitude ranging from 0.9 to 1.8 (it's a variable star). The ancient Greek for "against Mars" (roughly, anti-Ares) became the modern day name of Antares. About 600 LY away, it is also the 16th brightest star in the sky, even though a large portion of its emitted energy is in the infrared wavelengths. Its companion Antares B is a B2.5V star.
Aldebaran
(α Tauri, "the Bull's Eye")- A K5III star (giant, not main sequence) with an apparent magnitude of 0.87, Aldebaran is the 13th brightest star in the nighttime sky. It is around 65 LY away, and it has a white dwarf companion Aldebaran B, with a classification of M2V. The name Aldebaran is from Arabic for "the follower" (because it follows the Pleiades across the night sky). The nickname "the Bull's eye" comes from its bright orange color and its position in the "Bull's head" asterism.
Polaris
(α Ursae Minoris, "North Star", the "Pole Star")- Polaris is an important star for navigation, however, it is only approximate North. Polaris A is a F7I-II star, while companions Polaris B and Ab are a F-class main sequence star and a dwarf, respectively (there are also 2 farther stars, Polaris C and D). Polaris may be part of a loose cluster of A- and F-class stars.
Spica
(α Virginis)- A B1III-IV star with an apparent magnitude varying between 0.92 and 1.04 over a 4-day period of time. Spica is a binary star system (companion Spica B is a B2V star) about 260 LY away. Its name comes from Latin for "Virgo's ear of grain".
Pollux
(β Gem, β Geminorum, Beta Geminorum) is an orange giant star approximately 34 light-years from the Earth in the constellation of Gemini (the Twins). Pollux is the brightest star in the constellation, brighter than Castor (Alpha Geminorum). In 2006, Pollux was confirmed to have an extrasolar planet orbiting it, making it the brightest star in the sky with a known planet, other than the Sun.
Rigel
(β Orionis)- Named in Arabic "left foot of the central one", Rigel is an important star for navigation. Somewhere between 700 and 900 LY away, Rigel is also known as the most luminous star in the nearby Milky Way. Most of the time, it is the brightest star in Orion, but Betelgeuse can be brighter because it is a variable star. Rigel is known to be a triple star system, however, it may in fact be a quadruple star system. The most prominent star is a B8I star with an apparent magnitude of 0.11.
Algol
(β Persei, the "Demon Star")- A triple star system, with Algol A as a B8V star, Algol B as a K0-2III star, and Algol C as a A5V star. Combined, it has an apparent magnitude of 2.1, which drops to 3.4 every 3 days or so when Algol A is eclipsed by Algol B (called an eclipsing binary). "Algol" is from Arabic for "head of the ghoul"- they saw the star as the head of Medusa (the Gorgon who turned anyone she looked at into stone).
Gliese 581
A red dwarf star located in Libra. It is famous for its planetary system. Located 20.3 LY away from Earth with a spectral type of M3V, meaning it is at the far end of the M-class. It is a third the size of out sun.
Mizar
The Mizar-Alcor stellar sextuple system consists of the quadruple system Mizar and the binary system Alcor. Mizar (ζ UMa, ζ Ursae Majoris) is a quadruple system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A1V. Mizar's name comes from the Arabic مئزر mīzar, meaning a waistband or girdle.)
