Stars

• Giant gas cloud or stellar nebula


  Origin of a star, low temperature allows synthesis of molecules, e.g. Orion Cloud Complex
• Protostar


  Warm clump of molecules formed as gas particles in molecular cloud run into each other, can form multiple protostars in one cloud
• T Tauri phase

  Begins when material stops falling into protostar, releases energy from gravitational contraction, lasts ~100 million years
• Main sequence

  Most extended phase, core temperature reaches fusion, hydrogen converted to helium, exothermic reaction releases energy, low mass stars burn hydrogen slowly and stay longest, medium mass stars stay billions of years, high mass stars exit after a few million years
• Red giant and red supergiant

  For low and medium mass stars: Red giant - nuclear radiation ceases as hydrogen in core is fused, outer layers expand and cool, can last up to a billion years. Planetary nebula - core heats up, helium fusion occurs, outer layers expelled in explosion.
• Red supergiant


  For high mass stars: Core temperatures high enough for fusion even after helium exhausted, can swell to spectacular sizes, fusion continues until iron forms, no further fusion possible
• White dwarf

  For low and medium mass stars: As outer layers shed, tiny core of carbon and oxygen remains, extremely dense due to electron pressure, only if core <1.4 solar masses
• Supernova


  For high mass stars: Core turns to iron, collapses under gravity, triggers incredible explosion, fuses iron and creates heavier elements
• Black dwarf


  Final stage of low and medium mass stars, remnants of white dwarfs that have burned remaining fuel, strictly theoretical as none have formed yet
• Neutron star


  If collapsing core 1.4-3 solar masses, extremely dense body of neutrons formed as electrons pushed into nuclei
• Black hole


  If collapsing core >3 solar masses, gravity so strong nothing can escape, pulls in neighboring stars and planets
• Polaris


  Also known as the North Star, Pole Star, Lodestar, and Guiding Star
• Polaris


  • 48th brightest star in the night sky
  • Very close to the north celestial pole and used as a navigational tool in the Northern Hemisphere
  • Scientifically, this star is Alpha Ursae Minoris, the alpha star in the Ursa Minor constellation
  • Approximately 430 to 447 light-years away from Earth
  • Its luminosity as a white supergiant makes it highly visible from Earth
  • A trinary star system comprised of a main star (alpha UMi Aa) and two smaller stars (alpha UMi B and alpha UMi Ab)
  • It became the North Star subject to Earth's movement, pointing to different directions
  • Since it is a Cepheid variable star, its distance to the Sun changes
• Sirius


  Also known as the Dog Star, the brightest star in Canis Major
• Sirius


  • The brightest star in the night sky
  • It is a binary star system consisting of a white main sequence star, Sirius A, and a faint white dwarf companion, Sirius B
  • Its brightness is due to its luminosity and distance, being one of Earth's closest neighbor at an estimated 8.6 light-year distance
  • This was seen as a signal for the flooding of Nile in ancient Egypt
  • In Greece, the rising of Sirius in the sky was a sign of the "dog days of summer (a hot summer weather)"
  • To Polynesians from the southern hemisphere, this marked the approach of winter and was an important star for navigation in the Pacific Ocean
• Alpha Centauri System


  Also known as Rigel Kent or Toliman
• Alpha Centauri System


  • The brightest star in the southern constellation of Centaurus
  • The 3rd brightest star in the night sky
  • The closest star system to Earth, around 4.3 light-years away
  • A multi-star system consisting of Alpha Centauri A, B, and C or Proxima Centauri
  • Alpha Centauri A is a main sequence white dwarf that is slightly larger than the Sun
  • Alpha Centauri B is an orange subgiant that is slightly smaller and cooler than Alpha Centauri A
  • Proxima Centauri is a red dwarf star much smaller and fainter than the other two
  • Proxima Centauri is the closest to the Sun with a distance of 4.2 light-years
• Betelgeuse


  Also known as Alpha Orionis from the Orion constellation
• Betelgeuse


  • One of the largest and most luminous stars in the sky
  • A red supergiant star around 700 light-years away from Earth
  • Have possible companions orbiting it
  • Will one day go supernova (exact date unknown)
• Rigel


  Also known as Beta Orionis
• Rigel


  • The brightest star in the Orion constellation
  • 7th brightest star in the night sky
  • A multi-star system
  • Rigel A is a blue-white supergiant more massive than the Sun and very luminous (tens of thousands of times brighter than the sun)
  • Rigel A is a young star (somewhere in tens of millions of years old)
  • Rigel A is expected to go supernova when it reaches the end of its life
  • Rigel B is a binary system consisting of two (Rigel B and Rigel C) main sequence blue-white subdwarf stars
  • Rigel B is more massive than Rigel C
  • Rigel B's mass is less than Rigel A's but they are still all more massive than the sun
• Vega

  Anchors the Lyra constellation, also its brightest star
• Vega

  • The 5th brightest star in the night sky and second brightest in the northern celestial hemisphere
  • A part of the Summer Triangle in the northern hemisphere
  • A blue-white main sequence star roughly 2.1 times as massive as the Sun
  • A relatively close star at only 25 light-years away from Earth
  • The first star (other than the sun) to be photographed and the first to have its spectrum recorded
  • One of the stars whose distance was estimated through parallax measurements
  • Arguably the next most important star in the sky after the Sun
  • Believed to have a circumstellar disk of dust due to excess infrared radiations emission most likely as a result of collisions between objects in an orbiting debris disk
  • Stars that display infrared excess because of circumstellar dust are called "Vega-like stars"
  • Was used as the North Star thousands of years ago and will be so again around 13,727 CE
• Pleiades


  Also known as the Seven Sisters, Messier 45, and M45
• Pleiades


  • An open star cluster located in the Taurus constellation
  • Consists of over 1,000 confirmed members
  • 444 light-years from the Sun, one of the nearest star clusters to Earth, and the most visible to the naked eye
  • Dominated by young, hot blue stars
  • Brown dwarfs (just a fraction of the Sun's mass) account for 25% of its member stars
  • Estimated at between 75 and 150 million years old
• Antares

  Also known as Alpha Scorpii
• Antares


  • A red supergiant estimated to be 17 times more massive, 850 times larger (diameter) and 10,000 times more luminous than the Sun
  • One of the largest and most luminous observable star in the night sky
  • Resembles Mars in some aspects
  • Close to the ecliptic (imaginary band in the sky where the planets, Moon, and Sun move)
  • Approximately 550 light-years away from Earth and around 12 million years old
  • The 17th brightest star and the brightest star in the Scorpius constellation
  • One of the Royal Stars of Persia, the four stars that the ancient Persians believed to guard the four districts of the heaven
• Canopus


  Also known as Alpha Carinae
• Canopus


  • A white giant
  • The brightest star in the southern constellation of Carina (large constellation in the south) and the 2nd brightest star in the night sky
  • Over 300 light-years away from Earth
  • Associated with Agastya, a revered sage, in Vedic literature
  • Was known as the "Star of the Old Man" to the Chinese
  • Referred to as Suhayl by Islamic scholars as well as by the Bedouin people of Negev and Sinai and used as one of the principal stars for navigation at night
  • Commonly used for spacecraft to orient themselves in space since it is bright compared to the stars around it
• Aquarius


  Latin for "water carrier" or "cup carrier"
• Aquarius


  • Best viewed in October and located in the southern sky
  • Best seen in the fall in the Northern Hemisphere and in the spring in the Southern Hemisphere
  • One of the zodiac constellations (Jan. 20 to Feb. 8)
  • Associated with Ganymede, a beautiful Trojan youth who served as the cupbearer to the gods and was granted eternal youth and a place in the night sky
  • Home to several notable deep sky objects such as globular clusters, planetary nebulae, and galaxies (e.g. the Helix Nebula, Saturn Nebula, and Butterfly Nebula)
• Aries


  Latin for "ram"
• Aries


  • Outlines a faint head and horns of a ram
  • Best viewed in December
  • Best seen in the fall in the Northern Hemisphere and the spring in the Southern Hemisphere
  • One of the constellations of the zodiac (March 21 to April 19)
  • Associated with the ram whose fleece became the Golden Fleece, a symbol of kingship and authority and plays a significant role in the tale of Jason and the Argonauts where Jason was sent to find fleece to claim his throne as king
  • Most prominent stars: Hamal (a spectral binary star system that appears white) and Mesarthim (a binary star system with a combined magnitude, making it the second-brightest star)
• Canis Major


  Latin for "greater dog"
• Canis Major


  • Depicts a large dog following Orion, the hunter
  • Sirius, its brightest star and in the entire night sky, represents the dog's eye or nose
  • Best viewed in February
  • Best seen in the winter months in the Northern Hemisphere and visible all year-round from some locations in the Southern Hemisphere
  • A prominent constellation in the southern sky
  • Associated with the famed Greek dog Laelaps, a dog that was so fast that he was elevated to the skies by Zeus and also one of Orion's hunting dogs, trailing behind him in pursuit of Taurus, the bull
  • Home to several interesting stars: Adhara (a blue giant star hundreds of times more luminous than the sun) and Wezen (a binary star system with a combined magnitude, making it the third-brightest star)
  • Contains a portion of the Milky Way galaxy
• Cassiopeia


  Named after a queen in Greek Mythology
• Cassiopeia


  • Best viewed in November
  • Easy-to-find landmark in the sky as it is visible to the naked eye that can be looked for throughout the year in the Northern Hemisphere
  • A famous constellation that is easily recognizable due to its "W" shape
  • Because of its location, this has been used by sailors and explorers to navigate while its position would determine their direction
  • Associated with Cassiopeia, the mother of Princess Andromeda and a vain queen who bragged about her beauty and was punished by being placed in the sky forever, circling the North Star
• Gemini


  Latin for "twins"
• Gemini


  • Forms two stick figures standing side-to-side representing twins
  • Best viewed in February
  • Easily recognizable and visible to the naked eye in the night sky of the Northern Hemisphere during the winter months
  • One of the zodiac constellations (May 21 to June 20)
  • Associated with Leda's twins, Castor (son of the mortal king of Sparta) and Pollux (son of Zeus), when Castor was killed, the Pollux begged Zeus to give Castor immortality which he did by placing the brothers in the night sky
• Leo


  Latin for "lion"