Spring Triangle

The Spring Triangle is an astronomical asterism involving an imaginary triangle drawn upon the celestial sphere, with its defining vertices at Arcturus, Spica, and Regulus.[1] This triangle connects the constellations of Boötes, Virgo, and Leo. It is visible rising in the south eastern sky of the northern hemisphere between March and May.

The Spring Triangle with Arcturus, Spica, Regulus, and Denebola

George Lovi of Sky & Telescope magazine had a slightly different Spring triangle, including the tail of Leo, Denebola, instead of Regulus. Denebola is dimmer, but the triangle is more nearly equilateral.[2]

These stars form parts of a larger Spring asterism called the Great Diamond together with Cor Caroli.

The stars of the Spring Triangle

Constellation Name Apparent magnitude[3] Luminosity[3]
(L)
Spectral type[3] Distance[3]
(light-years)
BoötesArcturus −0.04103.75K1.5III37
VirgoSpica 1.041770B1V + B4V250
LeoRegulus 1.35134.28B7V79
Denebola 2.1413.43A3V36

Arcturus (α Boötes)

Arcturus is a giant orange star located in the constellation of Boötes. Located only 37 light-years away,[4] it has an apparent magnitude of -0.04.[5] It is the brightest star in the northern hemisphere and fourth brightest in the night sky.[6]

Arcturus found in the constellation Boötes

Due to its ability to be spotted easily, Arcturus was identified by ancient humans and tied to mythological ideals. The star was given its name from the ancient Greek Ἀρκτοῦρος (Arktouros), which translates to "Guardian of the Bear."[7] This name was selected because of the stars proximity to Ursa Major and Ursa Minor, surmising the two bear constellations were guarded by Arcturus.[8]

Arcturus is thought to be around 6 to 8.5 billion years old,[9] and has traveled up the red-giant branch of the Hertzsprung-Russell diagram, where it has expanded in size. The star is has a diameter of around 36 million km, making it around 26 times larger than the Sun.[10] Despite this size difference, the mass of Arcturus is only 1.1 times that of the Sun.

With a high speed of 122 km/s (or 270,000 mph) and movement not in the galactic plane most other stars move on, it is thought that Arcturus could have formed outside of the Milky Way.[11] This star is the namesake of a group of 52 other stars which share this similar proper motion, named the Arcturus moving group or Arcturus stream. It has been proposed that these stars are remnants of an ancient dwarf satellite galaxy that was assimilated into the Milky Way long ago.[12]

Spica (α Virginis)

Spica is a binary blue-white star pair that appears as a single point of light from Earth, so it is commonly referred to as a single star. The star system is 250 light-years away and has an apparent magnitude of 1.04.[13] It is the brightest star in the constellation Virgo, and is the 15th brightest star in the night sky.[14]

The name Spica is derived from a Latin phrase that describes the zodiac sign Virgo as holding an ear of grain, spīca virginis.[15] Virgo the Maiden is often represented as a young woman holding this stalk of grain. The best times of the year to view this star are during early spring to late summer in the northern hemisphere. To easily find this star, locate the Big Dipper and follow the curve of the handle. Following this path will first lead one to Arcturus. Finally, "drive a spike" directly to Spica.[16]

The constellation of Virgo

Spica is made up of two individual stars, Spica A and Spica B, with radii of 7.40 and 3.64 times the radius of the Sun, respectfully.[17] These sizes are large contributors to the brightness of the stars. Spica A has a luminosity of 12,100 that of our sun, while Spica B has a luminosity of 1,500.[18] Their size also leads to surface temperatures of 22,400 K and 18,500 K, much higher than the Sun. The stars have a small distance of only 0.12 AU, and an orbital period of only four days. This proximity gives gravity the effect of distorting both stars into being egg-shaped, where the pointed ends face the other star.[19]

Regulus (α Leo)

A look at the four star system of Regulus

Regulus, the brightest object found in the constellation of Leo, is a quadruple star system that is made up of two separate pairs of stars.[20] Lying at 79 light-years away, and with an apparent magnitude of 1.35, it is the 21st brightest star in the sky.[14] The name Regulus, which translates to "little king" in Latin, was given to the system by Polish astronomer Nicolaus Copernicus in the 16th-century.[21] The star can be seen at the base of head of Leo that looks like a backwards question mark, also referred to as the sickle.

The brighter pair of stars is called Regulus A, which is made of the large visible bright blue star and what is thought to be white dwarf, called Regulus D, but this is yet to be confirmed. This smaller companion has a mass of only 0.3 solar masses, while the larger has as mass of 3.8 solar masses. The pair have a small distance of 0.35 AU and short orbital period around a center mass of 40.11 days.[22] The other two stars, Regulus B and C, are main sequence orange dwarf and red dwarf, respectfully. With apparent magnitudes of 8.13 and 13.50, it is not possible for them to be seen with the naked eye.[23] This is the reason for the entire system to be named after the brightest star.

Regulus A appears to be egg-shaped due to extreme rotation speed. While our Sun rotates on its axis once every 27 days at a speed of 7,242 kph (4,500 mph), Regulus rotates every 16 hours at 1.1 million kph (700,000 mph). Astronomers have determined that if the star rotated 10% faster, it would rip itself apart.[24]

Denebola (β Leo)

Positions of stars Denebola and Regulus in Leo

Denebola is a white main sequence star seen in the constellation Leo. With a distance of 36 light-years from Earth, and an apparent magnitude of 2.14,[25] it is the third brightest star in the constellation and the 62nd in the night sky.[14] This star has also been observed as part of the Spring Triangle instead of Regulus. While Regulus has a higher magnitude, having Denebola as the third point of the triangle makes it more equilateral in appearance.

The stars name comes from the Arabic phrase Deneb Elased, or ðanab al-asad, meaning "the tail of the lion."[26] This refers to the stars position in the constellation, at the tail end of the lion Leo. Denebola has a mass of 1.78 solar masses and a radius of 1.728 solar radii, making it almost twice the size of our sun. It is thought to be a Delta Scuti type variable star due to the star having variations in brightness. Around 10 times a day there are fluctuations in brightness of magnitudes around 0.025.[27]

Deep Sky Objects

The Spring Triangle contains multiple objects of note, with a large amount of them belonging to the Virgo Cluster. This cluster contains around 1,500 galaxies and can be seen between the stars Denebola and Vindemiatrix, many of them being notable Messier objects.[1]

Messier 87

Supermassive black hole at the center of M87

The brightest galaxy seen in the cluster is the supergiant elliptical galaxy Messier 87. With an apparent magnitude if 9.6, the galaxy can be seen using a telescope, where it was first seen by Charles Messier in 1781. Located 54 million light-years away and 130,000 light-years across, M87 houses several trillions of stars and around 15,000 globular star clusters.[28] For comparison, our home Milky Way is 105,700 light-years across and contains around 200 billion stars.[29]

At the center of this galaxy, there is a supermassive black hole (6.5 billion solar masses) that forms a large blue jet of subatomic particles that are accelerated to speeds close to the speed of light.[30] In 2019, an image of this black hole, designated M87*[31] was published by the Event Horizon Telescope collaboration. This is of note, as it was the first picture of a black hole ever released.[32]

Messier 49

Messier 49 is the brightest galaxy in the Virgo group with an apparent magnitude of 9.4. This brightness allowed M49 to be the first observed in the group, by Nicolas Louis de Lacaille in 1752. The giant elliptical galaxy is located 56 million light-years from Earth, and is around 157,000 light-years across, with more than 200 billion stars.[33]

Siamese Twins Galaxies (NGC 4567 and NGC 4568)

Also known as the Butterfly Galaxies, NGC 4567 and 4586 are two unbarred spiral galaxies that are colliding. The pair were first discovered by astronomer William Herschel in 1784, but did not earn their name until observer Ralph Copeland called them the Siamese Twins in the late 1800s due to their almost identical shape and structure.[34] The galaxies are located around 52 million light-years away, with a separation between the cores of around 20,000 light-years.[35] The more distant galaxy, NGC 4567, has an apparent magnitude of 11.5 and is oriented almost completely face-on with our galaxy. While the closer, NGC 4568 has an apparent magnitude of 11.2 and is oriented at a diagonal. It was originally believed that the two were simply passing directly behind each other in the same line of sight, but further observations and studies have observed a high rate of star formation where the galaxies overlap, confirming that they undergoing the early phases of collision and merging.[36]

Other Objects

There are many other notable members in the triangle, including Messier 60, Messier 84, and Messier 86. Two named groups of galaxies are the Eyes Galaxies (NGC 4435 and NGC 4438) and the Leo Triplet (NGC 3628, Messier 65, Messier 66).[1]

See also

References

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  2. Spring Triangle
  3. "Brightest Stars". stars.astro.illinois.edu. Retrieved 2023-04-16.
  4. "EarthSky | Arcturus, brightest star of the north". earthsky.org. 2022-05-18. Retrieved 2023-02-25.
  5. Ducati, J. R. (2002-01-01). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. Bibcode:2002yCat.2237....0D.
  6. "Spring Triangle Asterism: Stars, Location, Features & More". The Planets. Retrieved 2023-02-25.
  7. Ramya, P.; Reddy, Bacham E.; Lambert, David L. (2012-09-05). "Chemical compositions of stars in two stellar streams from the Galactic thick disc". Monthly Notices of the Royal Astronomical Society. 425 (4): 3188–3200. arXiv:1207.0767. Bibcode:2012MNRAS.425.3188R. doi:10.1111/j.1365-2966.2012.21677.x. ISSN 0035-8711. S2CID 119253279.
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  9. Ramírez, I.; Allende Prieto, C. (2011-12-01). "Fundamental Parameters and Chemical Composition of Arcturus". The Astrophysical Journal. 743 (2): 135. arXiv:1109.4425. Bibcode:2011ApJ...743..135R. doi:10.1088/0004-637X/743/2/135. ISSN 0004-637X. S2CID 119186472.
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  12. Ibata, Rodrigo; Gibson, Brad (April 2007). "The Ghosts of Galaxies Past". Scientific American. 296 (4): 40–45. Bibcode:2007SciAm.296d..40I. doi:10.1038/scientificamerican0407-40. ISSN 0036-8733. PMID 17479629.
  13. "EarthSky | Spica, bright beacon of Virgo, is 2 stars". earthsky.org. 2021-07-15. Retrieved 2023-03-10.
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  20. Ian (2020-01-20). "Regulus (α Leonis) | Facts, Information, History & Definition". The Nine Planets. Retrieved 2023-03-21.
  21. Elizabeth Howell (2013-09-21). "Regulus: The Kingly Star". Space.com. Retrieved 2023-03-21.
  22. "EarthSky | Meet Regulus, the Lion's Heart". earthsky.org. 2022-05-06. Retrieved 2023-03-21.
  23. "Regulus Star - Facts & Features About The Little King". The Planets. Retrieved 2023-03-21.
  24. Tariq Malik (2005-01-31). "Leo's Bright Star Regulus Flies like Bullet". Space.com. Retrieved 2023-04-02.
  25. admin (2020-04-27). "Denebola (Beta Leonis): Star Type, Facts, Name, Location, Constellation | Star Facts". Retrieved 2023-04-16.
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