Canis Major is a constellation in the southern sky. Its name means ‘the greater dog’ in Latin. Canis Major is the 43rd biggest constellation in the sky, occupying an area of 380 square degrees. It is located in the second quadrant of the southern hemisphere (SQ1) and can be seen at latitudes between +60° and -90°. The neighboring constellations are Columba, Lepus, Monoceros, and Puppis.
[http://www.constellation-guide.com/constellation-list/canis-major-constellation/]
Canis Major on Chart XVIII of Johann Bode’s Uranographia (1801). Bode depicted the dog with Sirius marking its snout. Classical Greek descriptions, though, placed Sirius in the dog’s jaws.
[http://www.ianridpath.com/startales/canismajor.htm]
Commonly, Canis Major and Canis Minor represent the two dogs of Orion. The ancient Greeks refer only to one dog, but by Roman times, Canis Minor appears as Orion’s second dog.
The ancient Greeks observed that the appearance of Sirius heralded the hot and dry summer, and feared that it caused plants to wilt, men to weaken, and women to become aroused. Due to its brightness, Sirius would have been noted to twinkle more in the unsettled weather conditions of early summer. To Greek observers, this signified certain emanations which caused its malignant influence. Anyone suffering its effects was said to be astroboletos (ἀστροβόλητος) or ‘star-struck.’ It was described as ‘burning’ or ‘flaming’ in literature. The season following the star’s heliacal rising (i.e. rising with the Sun) came to be known as the Dog Days of summer.
The Romans knew these days as ‘dies caniculares’ (‘Dog Days’) and the star Sirius was called ‘Canicula’ (little dog). The excessive panting of dogs in hot weather was thought to place them at risk of desiccation and disease. In extreme cases, a foaming dog might have rabies, which could infect and kill humans whom they had bitten. The Romans celebrated the heliacal setting of Sirius around April 25, sacrificing a dog, along with incense, wine, and a sheep, to the goddess Robigo so that the star’s emanations would not cause wheat rust on wheat crops that year.
In ancient Egypt, Sirius was known as Sopdet (Greek: Σῶθις ‘Sothis’), is recorded in the earliest astronomical records. During the era of the Middle Kingdom, Egyptians based their calendar on the heliacal rising of Sirius, namely the day it becomes visible just before sunrise after moving far enough away from the glare of the Sun. This occurred just before the annual flooding of the Nile and the summer solstice, after a 70-day absence from the skies. The hieroglyph for Sothis features a star and a triangle. Sothis was identified with the great goddess Isis, who formed a part of a triad with her husband Osiris and their son Horus, while the 70-day period symbolized the passing of Isis and Osiris through the duat (Egyptian underworld).
In ancient Mesopotamia, Sirius, named KAK.SI.DI by the Babylonians, was seen as an arrow aiming towards Orion, while the southern stars of Canis Major and a part of Puppis were viewed as a bow, named BAN in the Three Stars Each tablets, dating to around 1100 BCE. In the later compendium of Babylonian astronomy and astrology titled MUL.APIN, the arrow, Sirius, was also linked with the warrior Ninurta, and the bow with Ishtar, daughter of Enlil. Ninurta was linked to the later deity Marduk, who was said to have slain the ocean goddess Tiamat with a great bow, and worshipped as the principal deity in Babylon.
In Iranian mythology, especially in Persian mythology and in Zoroastrianism, the ancient religion of Persia, Sirius appears as Tishtrya and is revered as the rain-maker divinity (Tishtar of New Persian poetry). Beside passages in the sacred texts of the Avesta, the Avestan language Tishtrya followed by the version Tir in Middle and New Persian is also depicted in the Persian epic Shahnameh of Ferdowsi. Due to the concept of the yazatas, powers which are ‘worthy of worship,’ Tishtrya is a divinity of rain and fertility and an antagonist of apaosha, the demon of drought. In this struggle, Tishtrya is beautifully depicted as a white horse.
Many nations among the indigenous peoples of North America also associated Sirius with canines; the Seri and Tohono O’odham of the southwest note the star as a dog that follows mountain sheep, while the Blackfoot called it ‘Dog-face.’ The Cherokee paired Sirius with Antares as a dog-star guardian of either end of the ‘Path of Souls.’ The Pawnee of Nebraska had several associations; the Wolf (Skidi) tribe knew it as the ‘Wolf Star,’ while other branches knew it as the ‘Coyote Star.’ Further north, the Alaskan Inuit of the Bering Strait called it ‘Moon Dog.’
Sirius is mentioned in Surah, An-Najm (‘The Star’), of the Qur’an, where it is given the name aš-ši‘rā or ash-shira; the leader). Ibn Kathir said in his commentary that “it is the bright star, named Mirzam Al-Jawza (Sirius), which a group of Arabs used to worship.” The alternate name Aschere, used by Johann Bayer, is derived from this.
In Chinese astronomy, the modern constellation of Canis Major lies in the Vermilion Bird (Nán Fāng Zhū Què), where the stars were classified in several separate asterisms of stars. Sirius was Tiānláng, the Celestial Wolf, denoting invasion and plunder. Southeast of the Wolf was the asterism Húshǐ, the celestial Bow and Arrow, which was interpreted as containing Delta, Epsilon, Eta and Kappa Canis Majoris and Delta Velorum. Alternatively, the arrow was depicted by Omicron2 and Eta and aiming at Sirius (the Wolf), while the bow comprised Kappa, Epsilon, Sigma, Delta and 164 Canis Majoris, and Pi and Omicron Puppis.
Both the Māori people and the people of the Tuamotus (Polynesia) recognized the figure of Canis Major as a distinct entity, though it was sometimes absorbed into other constellations. Te Huinga-o-Rehua, also called Te Putahi-nui-o-Rehua and Te Kahui-Takurua, (‘The Assembly of Rehua’ or ‘The Assembly of Sirius’) was a Maori constellation that included both Canis Minor and Canis Major, along with some surrounding stars. They called Sirius Rehua and Takarua, corresponding to two of the names for the constellation, though Rehua was a name applied to other stars in various Maori groups and other Polynesian cosmologies. The Tuamotu people called Canis Major Muihanga-hetika-o-Takurua, ‘the abiding assemblage of Takurua.’
The Tharumba people of the Shoalhaven River (Australia) saw three stars of Canis Major as Wunbula (Bat) and his two wives Murrumbool (Mrs Brown Snake) and Moodtha (Mrs Black Snake); bored of following their husband around, the women try to bury him while he is hunting a wombat down its hole. He spears them and all three are placed in the sky as the constellation Munowra. To the Boorong people of Victoria, Sigma Canis Majoris was Unurgunite, and its flanking stars Delta and Epsilon were his two wives. The moon (Mityan, ‘native cat’) sought to lure the further wife (Epsilon) away, but Unurgunite assaulted him and he has been wandering the sky ever since.
In the religion of the Serer people of Senegal, The Gambia and Mauritania, Sirius is called Yoonir from the Serer language (and some of the Cangin language speakers, who are all ethnically Serers). The star Sirius is one of the most important and sacred stars in Serer religious cosmology and symbolism. The Serer high priests and priestesses, (Saltigues, the hereditary ‘rain priests’) chart Yoonir in order to forecast rain fall and enable Serer farmers to start planting seeds. In Serer religious cosmology, it is the symbol of the universe.
In Theosophy, it is believed the Seven Stars of the Pleiades transmit the spiritual energy of the Seven Rays from the Galactic Logos to the Seven Stars of the Great Bear, then to Sirius. From there is it sent via the Sun to the god of Earth (Sanat Kumara), and finally through the seven Masters of the Seven Rays to the human race.
Another story related to Sirius is that of the Dogon people of Mali, West Africa, reported by some researchers to have traditional astronomical knowledge about Sirius that would normally be considered impossible without the use of telescopes. According to Marcel Griaule, who had studied the Dogon people, they knew about the fifty-year orbital period of Sirius and its companion prior to western astronomers. They also refered to a third star accompanying Sirius A and B. Robert Temple, who popularized the story with his 1976 book ‘The Sirius Mystery,’ credits the Dogon people with knowledge of the four Galilean moons of Jupiter and the rings of Saturn. This has been the subject of controversy and speculation. Noah Brosch explained in his book ‘Sirius Matters’ that the cultural transfer of relatively modern astronomical information could have taken place in 1893, when a French expedition arrived in Central West Africa to observe the total eclipse on April 16.
The Winter Triangle: Procyon (top left), Betelgeuse (top right), Sirius (base). Image: Hubble European Space Agency.
[http://www.constellation-guide.com/sirius-the-dog-star/]
[https://en.wikipedia.org/wiki/Winter_Hexagon]
The star Sirius of Canis Major together with Procyon of Canis Minor and Betelgeuse of Orion form the Winter Triangle, as seen in the northern hemisphere. An extension of the Winter Triangle is the Winter Hexagon, with vertices at Rigel of Orion, Aldebaran of Taurus, Capella of Auriga, Pollux of Gemini, Procyon of Canis Minor, and Sirius of Canis Major. The Winter Triangle in the tropics and southern hemisphere, can be extended with the bright star Canopus in the south (then called ‘Summer Hexagon’).
[http://oneminuteastronomer.com/5312/constellation-canis-major/]
[http://astropixels.com/constellations/charts/CMa.html]
An artist’s impression of Sirius A and Sirius B. Sirius A is the larger of the two stars.
The Sirius system contains two of the eight nearest stars to the Solar System (not including the Sun), and is the fifth closest stellar system to ours (again not including the Sun). This proximity is the main reason for its brightness, as with other near stars such as Alpha Centauri and in stark contrast to distant, highly luminous super-giants such as Canopus, Rigel or Betelgeuse. However, it is still around 25 times more luminous than the Sun. The closest large neighboring star to Sirius is Procyon, 1.61 parsecs (5.24 ly) away. The Voyager 2 spacecraft, launched in 1977 to study the four Jovian planets in the Solar System, is expected to pass within 4.3 light-years (1.3 pc) of Sirius in approximately 296,000 years.
Sirius is the brightest star in the Earth’s night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name is derived from the Ancient Greek Σείριος (Seirios), meaning ‘glowing’ or ‘scorcher’ (because it marked the season of greatest heat). What the naked eye perceives as a single star is actually a binary star system, consisting of a white main-sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, called Sirius B. The distance separating Sirius A from its companion varies between 8.2 and 31.5 AU.
Sirius can even be observed in daylight with the naked eye under the right conditions. Ideally, the sky should be very clear, with the observer at a high altitude, the star passing overhead, and the Sun low down on the horizon. These observing conditions are more easily met in the southern hemisphere, due to the southerly declination of Sirius.
Sirius appears bright because of both its intrinsic luminosity and its proximity to Earth. At a distance of 2.6 parsecs (8.6 ly), as determined by the Hipparcos astrometry satellite, the Sirius system is one of Earth’s near neighbors. Sirius is gradually moving closer to the Solar System, so it will slightly increase in brightness over the next 60,000 years. After that time its distance will begin to increase and it will become fainter, but it will continue to be the brightest star in the Earth’s sky for the next 210,000 years.
Sirius A is about twice as massive as the Sun, and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun but has a significantly lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.
The orbit of Sirius B around A as seen from Earth (slanted ellipse). The wide horizontal ellipse shows the true shape of the orbit (with an arbitrary orientation) as it would appear if viewed straight on.
Sirius B, is a star that has already evolved off the main sequence and become a white dwarf. Currently 10,000 times less luminous in the visual spectrum, Sirius B was once the more massive of the two. With a mass nearly equal to the Sun’s, Sirius B is one of the more massive white dwarfs known. Yet that same mass is packed into a volume roughly equal to the Earth’s. The current surface temperature is 25,200 K. However, because there is no internal heat source, Sirius B will steadily cool as the remaining heat is radiated into space over a period of more than two billion years. The age of the system has been estimated at around 230 million years. Early in its lifespan it was thought to have been two bluish white stars orbiting each other in an elliptical orbit every 9.1 years.
[https://en.wikipedia.org/wiki/Sirius]
Epsilon Canis Majoris
Epsilon Canis Majoris is the second brightest star in the constellation Canis Major, and one of the brightest stars in the night sky. It has the traditional name Adhara (sometimes spelled Adara). The name is from the Arabic word ‘aðāra,’ ‘virgins.’
Adhara is a binary star, estimated to lie about 430 light years away from Earth. The main star possesses an apparent magnitude of +1.5 and belongs to the spectral classification B2. Its color is blue or blueish-white, due to the surface temperature of 22,200K. It emits a total radiation equal to 38,700 times that of the Sun. This star is the brightest known extreme ultraviolet source in the night sky. It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud.
The +7.5 magnitude companion star (the absolute magnitude amounts to +1.9) is at 7.5" away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the main star is approximately 250 times brighter than its companion.
A few million years ago, Adhara was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4,700,000 years ago, Adhara was 34 light years from the Sun, and was the brightest star in the sky with a magnitude of –3.99. No other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.
[https://en.wikipedia.org/wiki/Epsilon_Canis_Majoris]
Artist’s illustration of δ CMa, a yellow supergiant 1800 light-years away in the Canis Major constellation.
Delta Canis Majoris has the traditional name Wezen, Wesen, or Wezea. The name is derived from the Arabic ‘al-wazn,’ which means ‘weight.’ It is a yellow-white F-type supergiant with an apparent magnitude of +1.83, and it is the third brightest star in the constellation after Sirius and Adhara. It lies around 1,600 light-years away.
Wezen is a supergiant of class F8 with a radius around 237 times that of the Sun. Its surface temperature is around 5,818 K, and it weighs around 17 solar masses. Its absolute magnitude is –6.87. It is rotating at a speed of around 28 km/s, and hence may take a year to rotate fully. Only around 10 million years old, Wezen has stopped fusing hydrogen in its core. Its outer envelope is beginning to expand and cool, and in the next 100,000 years it will become a red supergiant as its core fuses heavier and heavier elements. Once it has a core of iron, it will collapse and explode as a supernova.
As with the rest of Canis Major, Wezen is most visible in winter skies in the northern hemisphere, and summer skies in the southern. In Bayer’s Uranometria, it is in the Great Dog’s hind quarter. If Wezen were as close to Earth as Sirius is, it would be as bright as a half-full moon. The open cluster NGC 2354 is located only 1.3 degrees east of Delta Canis Majoris.
[https://en.wikipedia.org/wiki/Delta_Canis_Majoris]
Beta Canis Majoris has the traditional name Murzim, Al-Murzim or Mirzam, which is Arabic for ‘The Herald,’ and probably refers to its position, heralding Sirius in the night sky (i.e., rising before it). In the modern constellation it lies at the position of the dog’s head. It is located at a distance of about 500 light-years (150 parsecs) from the Earth.
Murzim is a Beta Cephei variable that varies in apparent magnitude between +1.97 and +2.01 over a six-hour period, a change in brightness that is too small to be discerned with the naked eye. It exhibits this variation in luminosity because of periodic pulsations in its outer envelope, which follow a complex pattern with three different cycles; all about six hours in length. The two dominant pulsation frequencies have a combined beat period of roughly 50 days. The strongest pulsation mode is a radial first overtone, while the second is non-radial.
This star has a mass of about 13- 14 times the mass of the Sun with 8- 11 times the Sun’s radius. The effective temperature of the star’s outer envelope is about 23,150 K, which is much higher than the Sun’s at 5,778 K. The energy emitted at the high temperature of the former is what gives this star a blue-white hue characteristic of a B-type star. The estimated age of Murzim is 12- 13 million years, which is long enough for a star of this mass to have evolved into a giant star. The stellar classification of B1 II-III indicates that the spectrum matches a star part way between a giant star and a bright giant.
Beta Canis Majoris is located near the far end of the Local Bubble, a cavity in the local interstellar medium through which the Sun is traveling.
[https://en.wikipedia.org/wiki/Beta_Canis_Majoris]
Eta Canis Majoris, a blue Supergiant in Canis Major
Eta Canis Majoris has the traditional name Aludra, which originates from the Arabic ‘al-adhraa,’ ‘the virgin.’ This star, along with ε CMa (Adhara), δ CMa (Wezen) and ο2 CMa (Thanih al Adzari), were ‘Al ʽAdhārā,’ the Virgins. Its distance is approximately 2,000 ly (600 pc).
Aludra shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter (absolute magnitude) than the Sun. A blue-white supergiant of spectral type B5Ia, Aludra has a luminosity 176,000 times and a diameter around 80 times that of the Sun. It has a mass 19.19 times and luminosity 105,442 times that of the Sun. It has only been around a fraction of the time our Sun has, yet is already in the last stages of its life. It is still expanding and may become a red supergiant, or perhaps has already passed that phase, but in either case it will become a supernova within the next few million years.
Aludra is classified as an Alpha Cygni type variable star and its brightness varies from magnitude +2.38 to +2.48 over a period of 4.7 days.
[https://en.wikipedia.org/wiki/Eta_Canis_Majoris]
Actual image of VY Canis Majoris (brightest star in the image) and its surrounding molecular cloud complex in the open cluster NGC 2362 as seen from the Rutherfurd Observatory of the Columbia University in New York.
VY Canis Majoris is a red hypergiant star. It is one of the largest stars (at one time it was the largest known) and also one of the most luminous of its type, and has a radius of approximately 1,420 solar radiuses (990,000,000 km; 6.6 au), and is located about 1.2 kiloparsecs (3,900 light-years) from Earth.
VY Canis Majoris is a single star categorized as a semiregular variable with an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m3. If placed at the center of the Solar System, VY Canis Majoris’s surface would extend beyond the orbit of Jupiter, although there is still considerable variation in estimates of the radius.
During the 19th century, observers measured at least six discrete components, suggesting that it might be a multiple star. These discrete components are now known to be bright areas in the surrounding nebula. Visual observations in 1957 and high-resolution imaging in 1998 showed that there are no companion stars.
VY Canis Majoris is a high-luminosity M star with an effective temperature of about 3,500 K, placing it at the upper-right hand corner of the Hertzsprung- Russell diagram and meaning it is a highly evolved star. During its main sequence, it would have been an O-type star with a mass of 15 to 35 solar masses.
In 2006, University of Minnesota Professor Roberta M. Humphreys used the spectral energy distribution distance of VY Canis Majoris to calculate its luminosity. Since most of the radiation coming from the star is reprocessed by the dust in the surrounding cloud, she integrated the total fluxes over the entire nebula and showed that VY Canis Majoris has a luminosity 5.6×10^5 times that of the sun. More recent estimates of the luminosity using a variety of methods give somewhat lower values. Humphreys originally estimated the radius of VY CMa at 1,800-2,100 solar radii, which made it the largest star then known. A more recent and accurate VLTI measurement gives the star a radius of 1,420 ± 120 solar radii.
In 1976, Charles J. Lada and Mark J. Reid published the discovery of a bright-rimmed molecular cloud 15 minutes of arc east of VY Canis Majoris. Lada and Reid assumed the distance of the molecular cloud is approximately equal to that of the stars, which are members of the open cluster NGC 2362, that ionize the rim. NGC 2362 has a distance of 1.5 ± 0.5 kiloparsecs as determined from its color-magnitude diagram. VY CMa is projected onto the tip of the cloud rim, suggesting its association with the molecular cloud. In addition to that, the velocity of the molecular cloud is very close to the velocity of the star. This further indicates the association of the star with the molecular cloud, and consequently with NGC 2362, which means VY Canis Majoris is at the same distance. A more recent measurement of the distance to NGC 2362 gives 1.2 kiloparsecs.
VY Canis Majoris ejects huge amounts of gas during its outbursts
VY Canis Majoris is surrounded by an extensive nebula, which contains condensations that were once regarded as companion stars. The nebula has been extensively studied with the aid of the Hubble Space Telescope. It has a complex structure that includes filaments and arcs, which were caused by past eruptions; this structure is similar to that of the nebula surrounding the yellow hypergiant IRC+10420. The similarity has led astronomers to propose that VY CMa will itself become a yellow hypergiant, then a luminous blue variable, and finally a Wolf- Rayet star, if it does not explode as a supernova first. Multiple asymmetric mass loss events are deduced to have occurred within the last 1,000 years. The mass loss is due to strong convection in the tenuous outer layers of the star, associated with magnetic fields. This is similar to the sunspots and coronal ejections of the Sun but on a much larger scale.
[https://en.wikipedia.org/wiki/VY_Canis_Majoris]
XMM-Newton image of pulsar ‘RX J0720.4-3125’
[http://www.esa.int/spaceinimages/Images/2006/04/XMM-Newton_image_of_pulsar_RX_J0720.4-3125]
RX J0720.4-3125 is a neutron star in the constellation Canis Major. It was discovered in 1997 in the ROSAT All-sky survey. Measurement of its parallax leads to an estimate of around 360 parsecs (1174 light-years) for its distance from Earth. It is a member of the Magnificent Seven, a group of neutron stars that are relatively near to the Solar System. RX J0720.4-3125 has a radius of around 5 km. Its spectrum and temperature appear to be mysteriously changing over several years. The nature of the changes are unclear, but it is possible there was an event such as the star’s absorption of an accretion disc.
[https://en.wikipedia.org/wiki/RX_J0720.4-3125]
Artist’s impression of PSR J0737-3039 double pulsar. The objects are not shown to scale: if they were depicted as the size of marbles, they would be 225 m (750 ft) apart.
PSR J0737-3039 is the only known double pulsar. It consists of two neutron stars emitting electromagnetic waves in the radio wavelength in a relativistic binary system. The two pulsars are known as PSR J0737-3039A and PSR J0737-3039B. It was discovered in 2003 at Australia’s Parkes Observatory by an international team led by the radio astronomer Marta Burgay during a high-latitude pulsar survey.
A pulsar is a neutron star which produces pulsating radio emission due to a strong magnetic field. A neutron star is the ultra-compact remnant of a massive star which exploded as a supernova. Neutron stars have a mass more than our sun, yet are only a few kilometers across. These extremely dense objects rotate on their axes, producing focused electromagnetic waves which sweep around the sky in a lighthouse effect at rates that can reach a few hundred pulses per second.
PSR J0737-3039 is the only known system containing two pulsars- thus a ‘double pulsar’ system. The object is similar to PSR B1913+16, which was discovered in 1974 by Taylor and Hulse, and for which the two won the 1993 Nobel Prize in Physics. Objects of this kind enable precise testing of Einstein’s theory of general relativity, because the precise and consistent timing of the pulsar pulses allows relativistic effects to be seen when they would otherwise be too small. Most such binary systems are thought to consist of one pulsar and one neutron star; J0737-3039 is the first case where both components are known to be not just neutron stars but pulsars.
The orbital period of J0737-3039 (2.4 hours) is the shortest yet known for such an object (one-third that of the Taylor-Hulse object), which enables the most precise tests yet. In 2005, it was announced that measurements had shown an excellent agreement between general relativity theory and observation. In particular, the predictions for energy loss due to gravitational waves appear to match the theory. As a result of energy loss due to gravitational waves, the common orbit shrinks by 7 mm per day. The two components will coalesce in about 85 million years. The pulses from Pulsar B are only detectable for about 20 minutes in each 2.4 hours orbit, since plasma in the magnetosphere of Pulsar A eclipses them over the rest of the orbit.
In addition to the importance of this system to tests of general relativity, Piran and Shaviv have shown that the young pulsar in this system must have been born with no mass ejection, implying a new process of neutron star formation that does not involve a supernova. Whereas the standard supernova model predicts that the system will have a proper motion of more than hundred km/s, they predicted that this system would not show any significant proper motion. Their prediction was later confirmed by pulsar timing.
Another great discovery from the double pulsar is the observation of an eclipse from a conjunction of the superior and weaker pulsar. This happens when the doughnut shaped magnetosphere of one pulsar, which is filled with absorbing plasma, blocks the companion pulsar’s light. The blockage, lasting more than 30 s, is not complete, due to the orientation of the plane of rotation of the binary system relative to Earth and the limited size of the weaker pulsar’s magnetosphere; some of the stronger pulsar’s light can still be detected during the eclipse.
[https://en.wikipedia.org/wiki/PSR_J0737-3039]
Seven star systems have been found to have planets. Nu2 Canis Majoris is an ageing orange giant of spectral type K1III of apparent magnitude 3.91 located around 64 light-years distant. Around 1.5 times as massive and 11 times as luminous as the Sun, it is orbited over a period of 763 days by a planet 2.6 times as massive as Jupiter. HD 47536 is likewise an ageing orange giant found to have a planetary system- echoing the fate of the Solar System in a few billion years as the Sun ages and becomes a giant. Conversely, HD 45364 is a star 107 light-years distant that is a little smaller and cooler than the Sun, of spectral type G8V, which has two planets discovered in 2008. With orbital periods of 228 and 342 days, the planets have a 3:2 orbital resonance, which helps stabilise the system. HD 47186 is another sunlike star with two planets; the inner- HD 47186 b- takes four days to complete an orbit and has been classified as a Hot Neptune, while the outer- HD 47186 c- has an eccentric 3.7-year period orbit and has a similar mass to Saturn. HD 43197 is a sunlike star around 183 light-years distant that has a Jupiter-size planet with an eccentric orbit.
Z Canis Majoris is a star system a mere 300,000 years old composed of two pre-main-sequence stars- a FU Orionis star and a Herbig Ae/Be star, which has brightened episodically by two magnitudes to magnitude 8 in 1987, 2000, 2004 and 2008. The more massive Herbig Ae/Be star is enveloped in an irregular roughly spherical cocoon of dust that has an inner diameter of 20 AU (3.0×109 km) and outer diameter of 50 AU (7.5×109 km). The cocoon has a hole in it through which light shines that covers an angle of 5 to 10 degrees of its circumference. Both stars are surrounded by a large envelope of in-falling material left over from the original cloud that formed the system. Both stars are emitting jets of material, that of the Herbig Ae/Be star being much larger- 11.7 light-years long. Meanwhile, FS Canis Majoris is another star with infra-red emissions indicating a compact shell of dust, but it appears to be a main-sequence star that has absorbed material from a companion. These stars are thought to be significant contributors to interstellar dust.
The stars of NGC 2362 surrounding τ CMa (Infrared image taken by the Spitzer Space Telescope)
NGC 2362 is an open cluster in the constellation Canis Major. It was discovered by Giovanni Batista Hodierna before 1654. Its brightest star is Tau Canis Majoris, and therefore it is sometimes called the Tau Canis Majoris Cluster. NGC 2362 has a distance of 1.48 kpc and is a relatively young 4- 5 million years in age. It is a massive open cluster, with more than 500 solar masses. The cluster is in relation with the giant nebula Sh2-310, that lies at the same distance.
[https://en.wikipedia.org/wiki/NGC_2362]
M41
Messier 41 (M41) is a bright open star cluster located in Canis Major constellation. It lies near Sirius, the brightest star in the sky. Messier 41 has an apparent magnitude of 4.5 and lies at an approximate distance of 2,300 light years from Earth. It has the designation NGC 2287 in the New General Catalogue. M41 is very easy to find as it lies about 4 degrees south of Sirius, the Dog Star, one of the nearest stars to Earth. M41 can be seen in the same binocular field with Sirius and Nu-2 Canis Majoris, an evolved orange giant with a visual magnitude of 3.95. The cluster forms a triangle with the two stars. In clear, dark skies, it is visible to the naked eye. Messier 41 occupies an area of 38 arc minutes in apparent diameter, roughly the size of the full Moon. The cluster has a true diameter of 25 light years. Its estimated age is between 190 and 240 million years. M41 is moving away from us at 23.3 km/s. Messier 41 contains about 100 members, including several red giants and a number of white dwarfs. The brightest among the giant stars is a K3-type star with a visual magnitude of 6.3, visible near the centre of the cluster. The orange giant is about 700 times more luminous than the Sun. The hottest star in M41 has the spectral classification A0.
[http://www.messier-objects.com/messier-41/]
An artist’s impression of the Monoceros Ring, which wraps three times around the Milky Way.
A small, irregular galaxy with a mass of about a billion solar masses, the Canis Major dwarf galaxy is one of our closest neighbours, lying approximately 25,000 light years from the Sun and 42,000 light years from the centre of the Milky Way. Until recently, however, this dwarf galaxy lay unobserved behind the dust and gas in the disk of the Milky Way. It was only discovered during the Two-Micron All Sky Survey (2MASS) infrared survey, which allowed astronomers to see beyond the dust, in many regions for the first time.
Gravitational interactions with the Milky Way have stripped long tidal tails from the Canis Major dwarf galaxy, which have wrapped themselves around the Milky Way three times in a structure known as the ‘Monoceros Ring’. Several of the globular clusters found in the Milky Way are also thought to have come from the Canis Major dwarf, whose ultimate fate is to merge with the Milky Way over the next billion years or so. With a mass only 1% of that of the Milky Way, this is one of two minor mergers known to be currently occurring in the Milky Way. The other involves the Sagittarius dwarf galaxy.
[http://astronomy.swin.edu.au/cosmos/C/Canis+Major+Dwarf]
NGC 2359 (Thor’s Helmet)
This helmet-shaped cosmic cloud with wing-like appendages is popularly called Thor’s Helmet. Heroically sized even for a Norse god, Thor’s Helmet is about 30 light-years across. In fact, the helmet is more like an interstellar bubble, blown as a fast wind from the bright, massive star near the bubble’s center sweeps through a surrounding molecular cloud. Known as a Wolf-Rayet star, the central star is an extremely hot giant thought to be in a brief, pre-supernova stage of evolution. Cataloged as NGC 2359, the nebula is located about 15,000 light-years away in the constellation Canis Major. The sharp image, made using broadband and narrowband filters, captures striking details of the nebula’s filamentary structures. It shows off a blue-green color from strong emission due to oxygen atoms in the glowing gas.
[http://apod.nasa.gov/apod/ap140215.html]
Stars fleeing a cosmic crash
Astronomical pictures sometimes deceive us with tricks of perspective. Right in the centre of this image, two spiral galaxies appear to be suffering a spectacular collision, with a host of stars appearing to flee the scene of the crash in a chaotic stampede.
However, this is just a trick of perspective. It is true that two spiral galaxies are colliding, but they are millions of light-years away, far beyond the cloud of blue and red stars near the merging spiral. This sprinkling of stars is actually an isolated, irregular dwarf galaxy named ESO 489-056. The dwarf galaxy is actually much more distant than many bright stars in the foreground of the image, which are located much closer to us, in the Milky Way.
ESO 489-056 is located 16 million light-years from Earth in the constellation of Canis Major (The Greater Dog), in our local Universe. It is composed of a few billion red and blue stars- a very small number when compared to galaxies like the Milky Way, which is estimated to contain around 200 to 400 billion stars, or the Andromeda Galaxy, which contains a mind-boggling one trillion.
[https://www.spacetelescope.org/images/potw1332a/]
Galactic Get-Together Has Impressive Light Display
At this time of year, there are lots of gatherings often decorated with festive lights. When galaxies get together, there is the chance of a spectacular light show as is the case with NGC 2207 and IC 2163.
Located about 130 million light years from Earth, in the constellation of Canis Major, this pair of spiral galaxies has been caught in a grazing encounter. NGC 2207 and IC 2163 have hosted three supernova explosions in the past 15 years and have produced one of the most bountiful collections of super bright X-ray lights known. These special objects- known as ‘ultraluminous X-ray sources’ (ULXs)- have been found using data from NASA’s Chandra X-ray Observatory.
As in our Milky Way galaxy, NGC 2207 and IC 2163 are sprinkled with many star systems known as X-ray binaries, which consist of a star in a tight orbit around either a neutron star or a “stellar-mass” black hole. The strong gravity of the neutron star or black hole pulls matter from the companion star. As this matter falls toward the neutron star or black hole, it is heated to millions of degrees and generates X-rays.
ULXs have far brighter X-rays than most ‘normal’ X-ray binaries. The true nature of ULXs is still debated, but they are likely a peculiar type of X-ray binary. The black holes in some ULXs may be heavier than stellar mass black holes and could represent a hypothesized, but as yet unconfirmed, intermediate-mass category of black holes.
This composite image of NGC 2207 and IC 2163 contains Chandra data in pink, optical light data from the Hubble Space Telescope in red, green, and blue (appearing as blue, white, orange, and brown), and infrared data from the Spitzer Space Telescope in red.
The new Chandra image contains about five times more observing time than previous efforts to study ULXs in this galaxy pair. Scientists now tally a total of 28 ULXs between NGC 2207 and IC 2163. Twelve of these vary over a span of several years, including seven that were not detected before because they were in a ‘quiet’ phase during earlier observations.
The scientists involved in studying this system note that there is a strong correlation between the number of X-ray sources in different regions of the galaxies and the rate at which stars are forming in these regions. The composite image shows this correlation through X-ray sources concentrated in the spiral arms of the galaxies, where large amounts of stars are known to be forming. This correlation also suggests that the companion star in the binary systems is young and massive.
Colliding galaxies like this pair are well known to contain intense star formation. Shock waves- like the sonic booms from supersonic aircraft- form during the collision, leading to the collapse of clouds of gas and the formation of star clusters. In fact, researchers estimate that the stars associated with the ULXs are very young and may only be about 10 million years old. In contrast, our Sun is about halfway through its 10-billion-year lifetime. Moreover, analysis shows that stars of various masses are forming in this galaxy pair at a rate equivalent to form 24 stars the mass of our sun per year. In comparison, a galaxy like our Milky Way is expected to spawn new stars at a rate equivalent to only about one to three new suns every year.
[http://www.nasa.gov/mission_pages/chandra/galactic-get-together-has-impressive-light-display.html]
[https://en.wikipedia.org/wiki/Canis_Major]
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