A star is a luminious globe of gas, producing its own heat and light by nuclear reactions. Stars are held together by gravity.
The nearest star to Earth is the Sun.
Before the telescope was invented, various ancient and medieval scientists counted the number of stars. Tycho Brahe counted 777, Johannes Kepler reached 1005 and Ptolemy put the number at 1,056.
A supernova is when a huge star explodes. It usually happens when its nuclear fusion cannot hold the core against its own gravity. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months.
The supernova SN 1006 first appeared in the constellation Lupus and was widely seen on Earth beginning in the year 1006. It occurred 7,200 light years away. It was, in terms of apparent magnitude, the brightest stellar event in recorded history. The supernova's remnant was not identified until 1965.
The nearest star to Earth is the Sun.
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| False-color imagery of the Sun |
HISTORY
A supernova is when a huge star explodes. It usually happens when its nuclear fusion cannot hold the core against its own gravity. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months.
The supernova SN 1006 first appeared in the constellation Lupus and was widely seen on Earth beginning in the year 1006. It occurred 7,200 light years away. It was, in terms of apparent magnitude, the brightest stellar event in recorded history. The supernova's remnant was not identified until 1965.
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| SN 1006 supernova remnant |
William Cranch Bond and John Adams Whipple took the first photograph of a star other than the Sun on July 17, 1850. The star was Vega, and the photograph was taken at Harvard College Observatory. The photograph was a daguerreotype, which is a type of early photographic process. Daguerreotypes are made by exposing a silver-plated copper plate to light. The light causes the silver to react and create a negative image. The negative image is then developed and fixed, creating a positive image.
The photograph of Vega is very faint, but it is still visible. It is a significant achievement, as it was the first time that a star other than the Sun had been photographed.
American astronomer Annie Jump Cannon (December 11, 1863 – April 13, 1941) manually classified more stars in a lifetime than anyone else, around 350,000 stars. She could classify a single star, fully, in approximately 20 seconds, and used a magnifying glass for the majority of the (faint) stars.
On May 9, 1922, the International Astronomical Union formally adopted Annie Jump Cannon’s stellar classification system. With only minor changes having been made since, it is still the primary system in use today.
The Sun, at apparent magnitude of −27, is the brightest object in the sky.
Sirius (sometimes called the Dog Star) is the brightest star in the night sky. It is a binary star system in Canis Major, near Orion. It has an apparent magnitude of −1.46. Sirius is about twice as massive as the Sun and has an absolute magnitude of 1.42. It is 25 times more luminous than the Sun.
American astronomer Alvan Graham Clark first observed the faint white dwarf companion of Sirius on January 31, 1862. The white dwarf can be seen to the lower left in the picture below.
HD 140283 is a subgiant star about 190 light years away from the Earth in the constellation Libra. It is thought to be the oldest known star, being nearly as old as the universe itself. Once dubbed the "Methuselah Star" by the popular press due to its age, the star must have formed soon after the Big Bang.
Earendel, discovered in 2022 is the most distant individual star detected at 12.9 billion years from Earth. However, due to the expansion of the universe, the star is now 28 billion light-years away.
MACS J1149+2223 Lensed Star-1, also known as Icarus, is a blue supergiant observed through a gravitational lens is the second most distant individual star detected, at 9 billion light-years from Earth (redshift z=1.49; comoving distance of 14.4 billion light-years; lookback time of 9.34 billion years). The light observed from the star was emitted when the universe was about 30% of its current age of 13.8 billion years.
Alpha Centauri is the closest star system to the Solar System, being 4.37 light-years from the Sun. It consists of three stars: Alpha Centauri A and Alpha Centauri B, which form the binary star Alpha Centauri AB, and a small and faint red dwarf, Alpha Centauri C.
A car traveling 100 mph would take more than 29 million years to reach Alpha Centuri.
UY Scuti is a red supergiant and pulsating variable star in the constellation Scutum approximately 9,500 light-years from Earth. It is the largest known star by radius with an estimated radius of 1,708 solar radii (1.188×109 kilometres); thus a volume nearly 5 billion times that of the Sun. If placed at the center of the Solar System, its photosphere would at least engulf the orbit of Jupiter. Light takes 110 minutes to travel from one side to the other.
It would take 1,200 years to fly around UY Scuti in a 900km/h regular passenger airplane. If Earth was in its habitable zone, it would take 10.000 years for one full rotation, each season lasting 2500 years.
Neutron star PSR J1748-2446 is the fastest spinning celestial object in the universe. The star rotates 716 times every second, so its equator moves at about 25% the speed of light. It is also 50 trillion times the density of lead and has a magnetic field a trillion times stronger than the Sun’s.
The star Kepler 11145123 is so perfectly spherical that it's the roundest natural object ever measured.
The average number of stars we can see with the naked eye is around 10,000. This number is only the 0.000004% of all stars in the Milky Way galaxy.
On May 9, 1922, the International Astronomical Union formally adopted Annie Jump Cannon’s stellar classification system. With only minor changes having been made since, it is still the primary system in use today.
RECORDS
The Sun, at apparent magnitude of −27, is the brightest object in the sky.
Sirius (sometimes called the Dog Star) is the brightest star in the night sky. It is a binary star system in Canis Major, near Orion. It has an apparent magnitude of −1.46. Sirius is about twice as massive as the Sun and has an absolute magnitude of 1.42. It is 25 times more luminous than the Sun.
American astronomer Alvan Graham Clark first observed the faint white dwarf companion of Sirius on January 31, 1862. The white dwarf can be seen to the lower left in the picture below.
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| Hubble Space Telescope image of Sirius. By By NASA, ESA, H. Bond , and M. Barstow |
HD 140283 is a subgiant star about 190 light years away from the Earth in the constellation Libra. It is thought to be the oldest known star, being nearly as old as the universe itself. Once dubbed the "Methuselah Star" by the popular press due to its age, the star must have formed soon after the Big Bang.
Earendel, discovered in 2022 is the most distant individual star detected at 12.9 billion years from Earth. However, due to the expansion of the universe, the star is now 28 billion light-years away.
MACS J1149+2223 Lensed Star-1, also known as Icarus, is a blue supergiant observed through a gravitational lens is the second most distant individual star detected, at 9 billion light-years from Earth (redshift z=1.49; comoving distance of 14.4 billion light-years; lookback time of 9.34 billion years). The light observed from the star was emitted when the universe was about 30% of its current age of 13.8 billion years.
Alpha Centauri is the closest star system to the Solar System, being 4.37 light-years from the Sun. It consists of three stars: Alpha Centauri A and Alpha Centauri B, which form the binary star Alpha Centauri AB, and a small and faint red dwarf, Alpha Centauri C.
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| Alpha Centauri (left) and Beta Centauri (right) . By Skatebiker |
A car traveling 100 mph would take more than 29 million years to reach Alpha Centuri.
UY Scuti is a red supergiant and pulsating variable star in the constellation Scutum approximately 9,500 light-years from Earth. It is the largest known star by radius with an estimated radius of 1,708 solar radii (1.188×109 kilometres); thus a volume nearly 5 billion times that of the Sun. If placed at the center of the Solar System, its photosphere would at least engulf the orbit of Jupiter. Light takes 110 minutes to travel from one side to the other.
It would take 1,200 years to fly around UY Scuti in a 900km/h regular passenger airplane. If Earth was in its habitable zone, it would take 10.000 years for one full rotation, each season lasting 2500 years.
Neutron star PSR J1748-2446 is the fastest spinning celestial object in the universe. The star rotates 716 times every second, so its equator moves at about 25% the speed of light. It is also 50 trillion times the density of lead and has a magnetic field a trillion times stronger than the Sun’s.
The star Kepler 11145123 is so perfectly spherical that it's the roundest natural object ever measured.
FUN STAR FACTS
There are more stars in space than there are grains of sand on every beach on Earth.
Because it takes so long for their light to reach Earth, many of the stars you see at night are long gone.
Because it takes so long for their light to reach Earth, many of the stars you see at night are long gone.
A white dwarf is the final evolutionary stage of a star like our sun, where it has exhausted all its nuclear fuel and lost most of its mass. White dwarfs are extremely dense, with a mass similar to that of the sun but with a radius of only a few thousand kilometers (or a few thousand miles). They cool over time and eventually become black dwarfs.
A black dwarf is a theoretical stellar remnant, which no longer emits significant heat or light. But none are known to exist, because the universe is not old enough for any white dwarfs to have cooled to the point of becoming black dwarfs. The age of the universe, estimated to be around 13.8 billion years, is not sufficient for any star to complete the process of cooling and becoming a black dwarf.
Over time, theoretically, a white dwarf star will dwindle to a black dwarf – but given the time this takes to happen and the age of the universe this shouldn't have actually happened to any yet.
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