The Winter Triangle is an astronomical asterism formed from three of the brightest stars in the winter sky. It is an imaginary equilateral triangle drawn on the celestial sphere, with its defining vertices at Sirius, Betelgeuse, and Procyon, the primary stars in the three constellations of Canis Major, Orion, and Canis Minor, respectively. [1]
For much of the night in the northern winter, the Winter Triangle is high in the sky at mid-northern latitudes, but can also be seen during autumn in the early morning to the East. In the spring the winter triangle is visible early in the evening to the West before its stars set below the horizon. From the southern hemisphere it appears upside down and lower in the sky during the summer months. [2]
The Winter Triangle surrounds most of the faint constellation Monoceros, although its brightest stars are of fourth magnitude and hardly noticeable to the naked eye. The triangle includes two first magnitude stars, while Sirius is even brighter. The other bright stars of the winter sky lie around the triangle: Orion including Rigel; Aldebaran in Taurus; Castor and Pollux in Gemini; and Capella in Auriga.
| Name | Constellation | Apparent magnitude | Luminosity (L☉) | Spectral type | Distance (ly) |
|---|---|---|---|---|---|
| Sirius | Canis Major | −1.46 | 25.4 | A1 V | 8.6 |
| Betelgeuse | Orion | 0.50 | 90,000 - 150,000 | M2 Iab | 640 |
| Procyon | Canis Minor | 0.34 | 6.93 | F5 IV-V | 11.5 |
Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast to Canis Minor, the "lesser dog"; both figures are commonly represented as following the constellation of Orion the hunter through the sky. The Milky Way passes through Canis Major and several open clusters lie within its borders, most notably M41.
Canis Minor is a small constellation in the northern celestial hemisphere. In the second century, it was included as an asterism, or pattern, of two stars in Ptolemy's 48 constellations, and it is counted among the 88 modern constellations. Its name is Latin for "lesser dog", in contrast to Canis Major, the "greater dog"; both figures are commonly represented as following the constellation of Orion the hunter.
Lepus is a constellation lying just south of the celestial equator. Its name is Latin for hare. It is located below—immediately south—of Orion, and is sometimes represented as a hare being chased by Orion or by Orion's hunting dogs.
Procyon is the brightest star in the constellation of Canis Minor and usually the eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Minoris, which is Latinized to Alpha Canis Minoris, and abbreviated α CMi or Alpha CMi, respectively. As determined by the European Space Agency Hipparcos astrometry satellite, this system lies at a distance of just 11.46 light-years, and is therefore one of Earth's nearest stellar neighbors.
Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation whose recognition predates Greek culture; it is one of the 48 constellations identified by the Greek astronomer Ptolemy in the second century.
Sirius is the brightest star in the night sky. Its name is derived from the Greek word Σείριος, meaning lit. 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated α CMa or Alpha CMa. With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star. Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.
Taurus is one of the constellations of the zodiac and is located in the northern celestial hemisphere. Taurus is a large and prominent constellation in the Northern Hemisphere's winter sky. It is one of the oldest constellations, dating back to the Early Bronze Age at least, when it marked the location of the Sun during the spring equinox. Its importance to the agricultural calendar influenced various bull figures in the mythologies of Ancient Sumer, Akkad, Assyria, Babylon, Egypt, Greece, and Rome. Its old astronomical symbol is (♉︎), which resembles a bull's head.
Triangulum Australe is a small constellation in the far Southern Celestial Hemisphere. Its name is Latin for "the southern triangle", which distinguishes it from Triangulum in the northern sky and is derived from the acute, almost equilateral pattern of its three brightest stars. It was first depicted on a celestial globe as Triangulus Antarcticus by Petrus Plancius in 1589, and later with more accuracy and its current name by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.
The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day.
Cancer is one of the twelve constellations of the zodiac and is located in the Northern celestial hemisphere. Its old astronomical symbol is (♋︎). Its name is Latin for crab and it is commonly represented as one. Cancer is a medium-size constellation with an area of 506 square degrees and its stars are rather faint, its brightest star Beta Cancri having an apparent magnitude of 3.5. It contains ten stars with known planets, including 55 Cancri, which has five: one super-earth and four gas giants, one of which is in the habitable zone and as such has expected temperatures similar to Earth. At the (angular) heart of this sector of our celestial sphere is Praesepe, one of the closest open clusters to Earth and a popular target for amateur astronomers.
Orion is a prominent set of stars visible during winter in the northern celestial hemisphere. It is one of the 88 modern constellations; it was among the 48 constellations listed by the 2nd-century astronomer Ptolemy. It is named after a hunter in Greek mythology.
Messier 41 (also known as M41 or NGC 2287) is an open cluster in the constellation Canis Major. It is sometimes referred to as the Little Beehive Cluster. It was discovered by Giovanni Batista Hodierna before 1654 and was perhaps known to Aristotle about 325 BC. It lies about four degrees almost exactly south of Sirius, with which it forms a roughly equilateral triangle with Nu2 Canis Majoris to the west—all three figure in the same field in binoculars.
An asterism is an observed pattern or group of stars in the sky. Asterisms can be any identified pattern or group of stars, and therefore are a more general concept than the 88 formally defined constellations. Constellations are based on asterisms, but unlike asterisms, constellations outline and today completely divide the sky and all its celestial objects into regions around their central asterisms. For example, the asterism known as the Big Dipper comprises the seven brightest stars in the constellation Ursa Major. Another is the asterism of the Southern Cross, within the constellation of Crux.
Orion's Belt is an asterism in the constellation of Orion. Other names include the Belt of Orion, the Three Kings, and the Three Sisters. The belt consists of three bright and easily identifiable collinear star systems – Alnitak, Alnilam, and Mintaka – nearly equally spaced in a line, spanning an angular size of ~140′ (2.3°).
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. This triangle connects the constellations of Boötes, Virgo, and Leo. It is visible in the evening rising in the southeastern sky of the Northern Hemisphere between March and May and setting until August, while at morning rising and setting from November to the end of February.
Epsilon Canis Majoris is a binary star system and the second-brightest star in the constellation of Canis Major. Its name is a Bayer designation that is Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is the 22nd-brightest star in the night sky with an apparent magnitude of 1.50. About 4.7 million years ago, it was the brightest star in the night sky, with an apparent magnitude of −3.99. Based upon parallax measurements obtained during the Hipparcos mission, it is about 430 light-years distant from the Sun.
The Winter Hexagon or Winter Circle/Oval is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius. It is mostly upon the Northern Hemisphere's celestial sphere. On most locations on Earth, this asterism is visible in the evening sky at the equator from approximately December to June, and in the morning sky from July to the end of November, while in the evenings on the northern hemisphere it is less months visible between December and June, and on the southern hemisphere less months between July and November. In the tropics and southern hemisphere, this can be extended with the bright star Canopus in the south.
Gemini is one of the constellations of the zodiac and is located in the northern celestial hemisphere. It was one of the 48 constellations described by the 2nd century AD astronomer Ptolemy, and it remains one of the 88 modern constellations today. Its name is Latin for twins, and it is associated with the twins Castor and Pollux in Greek mythology. Its old astronomical symbol is (♊︎).
First-magnitude stars are the brightest stars in the night sky, with apparent magnitudes lower than +1.50. Hipparchus, in the 1st century BC, introduced the magnitude scale. He allocated the first magnitude to the 20 brightest stars and the sixth magnitude to the faintest stars visible to the naked eye.
The southern celestial hemisphere, also called the Southern Sky, is the southern half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form constellations, appears to rotate westward around a polar axis as the Earth rotates.