Sunday, May 13, 2007


THE CONSTELLATION LEO:
The constellation of Leo is ideally placed for observation in the late spring/early summer sky. After nightfall it lays almost due south, and the proximity of the planet Saturn to the constellation makes for interesting viewing.
The ancient Sumerians, Egyptians, Babylonians, Syrians, Jews, Hindus, Turks, Greeks and Romans all recognized this group of stars as a lion. In Chinese astronomy it was, however, represented as a horse, and some claim that the Incas recognized it as a springing puma. The Egyptian association of this constellation has provoked many possible explanations. One says that because the Sun is in Leo during the hottest time of the summer and the lions come to the Nile to cool themselves then that the constellation was named for the lion. Another theory is that the power of the Sun in midsummer led to its being associated with the most powerful of beasts. Pliny wrote that the Egyptians worshipped the stars of Leo because the waters of the Nile rose in its annual flood when the Sun entered Leo. The Sphinx was said to represent Leo's body with the head of the adjacent constellation of Virgo. This, however, is disputed as most Egyptologists maintain that the head represents one of the early kings or the god Harmachis.
The Greek legend of this constellation associates it with the Nemean Lion. The first labour of Heracles was to slay the lion which had been terrorizing the area around Nemea near Corinth and bring back its invulnerable skin. After attempts to slay the lion with arrows and a sword were unsuccessful Heracles threw away his weapons and wrestled with the lion. Some accounts say that he strangled it. Other accounts say that he broke its neck or that he thrust his arm down its throat and choked it. After he had killed the beast Heracles found that he couldn't skin it, but Athena, in the form of an old crone, came to him and suggested that he use the lion's own claws to do the job. After this he took to wearing the lion's skin as armour, and it was said that when he returned to Eurystheus who was his taskmaster for the twelve labours that the King was so frightened by his appearance that he hid in a large bronze jar. From this point the king only communicated with Heracles through a herald.
The Romans often associated this constellation with Bacchus, the god of wine, who was often dressed in a lion's skin. It is also supposed to be both the 'Lion of Judah' and the lion on the British coat of arms.
The most prominent star of Leo is Regulus(see above diagram). The name means "little king" as does its Greek name "Basiliskos". The name Regulus dates from the 15th century. Its Arabic name Qalb Al Asad means "heart of the lion", and it was often referred to in the same way in Latin as "Cor Leonis". The star is about 85 light years distant and is the faintest of the first magnitude stars with an apparent brightness of 1.4. It is a young blue dwarf star, only a few hundred million years old and has a mass of about 3.5 times that of the Sun. It spins very rapidly with a rotation period of only 15.9 hours. Regulus is actually a triplet system. Its two faint companions are a binary system that orbits Regulus A about every 130,000 years.
Regulus lays closest to the ecliptic of all the brightest (1st magnitude) stars in the sky. This means that it is regularly occulted by the Moon. The next occultation of Regulus is due for western Canada On June 19th. It will, unfortunately, occur during daylight (see following list). It may still, however, be visible given clear skies and a good telescope. The occultation will not be visible in the eastern part of Canada, but residents of the southern USA may be able to see the event in dark skies. If this event were to happen during darkness it would actually be quite spectacular from here in Winnipeg because Regulus will "skim" the edge of the Moon rather than being fully occulted. This means that it will "blink on and off" as it passes behind mountains on the Moon. This may be visible if you drive south or west of Winnipeg one or two hours. The further west (or south) you are the longer the period of occultation. Here is the schedule for major cities in western Canada.
City:
Winnipeg: 7:36 pm
Saskatoon: Disappears 6:02pm; reappears 6:43pm
Regina: Disappears 6:06pm; reappears 6:48pm
Edmonton: Disappears 5:47pm; reappears 6:39pm
Calgary: Disappears 5:45pm; reappears 6:45pm
Vancouver: Disappears 4:28pm; reappears 5:42pm
As a side note the present excellent conditions for viewing Saturn and its rings won't last very much longer. As May and June go by the position of this planet will be lower in the west, and by the end of June it will be too low for a decent telescopic view. At the end of June, however, there will be an outstanding conjunction of Saturn and Venus. On June 30th between 10 and 11 pm Venus and Saturn will be within a degree of each other in the lower western sky. This will be the closest planetary conjunction of the year.
But back to Leo. The second most visible star in the constellation is Denebola (see map above). The name is a contraction of the Arabic 'Deneb Alasad' which derives from "the tail of the lion" in that language. It is a blue white star with an apparent magnitude of 2.1. it is about 39 light years distant. Its apparent luminosity varies slightly over a period of a few hours. This star has a strong infrared excess which means that it has a disc of cool material about it like the disc from which our solar system formed.
Another named star in Leo is 'Algieba' (Gamma Leonis in the above diagram). This comes from the Arabic 'Al-Jabhah' which means "the forehead" even though its position in the constellation means that it is more part of "the mane" of Leo than the forehead. This star is actually a binary system with an apparent magnitude of 1.98. The two component stars have magnitudes of 3.3 and 3.5, but they sum up to a brighter star to the naked eye. With a telescope they are 4 arc seconds apart. One is an orange colour and the other is yellow-white in colour. The stars orbit each other with a period of about 500 years. Both these stars are giant stars that are about 36 light years from Earth.
There are a number of other named stars in Leo. Delta Leonis is called Zosma, meaning "the girdle" from its older Greek name meaning "hip". It is the northern vertex of the triangle marking the haunches of Leo. It is about 56 light years distant, with an apparent magnitude of 2.6 and is a blue-white subgiant. Zeta Leonis called Adhafera from the Arabic for "lock of hair" lies in the lion's mane directly above Algieba along the curve of the sickle that defines Leo's head.
It is a white giant star with apparent magnitude 3.4 and is about 115 light years away. Theta Leonis is called 'Coxa' from the Latin for "hip" or sometimes 'Cheratan' or 'Chort' from the Arabic for "two small ribs". It is the star that marks the right angle of the triangle that defines the lion's hindquarters. It is a blue-white main sequence star with an apparent magnitude of 3.3 and is about 78 light years away. Lambda Leonis (not shown in the above diagram) is called Alterf from the Arabic for "the glance" . It lies to the west(right) of the tip of the sickle (epsilon Leonis in the diagram above) that defines the lion's head. It is an orange main sequence star with an apparent magnitude of 4.3 and is about 260 light years distant. Mu Leonis, at the top of the sickle, is called Rasalas from the Arabic for "northern part of the lion's head". It is an orange giant star with a magnitude of 3.9 and a distance of 180 light years. Finally there is Omicron Leonis to the west (right) of Regulus in the above diagram. This star is called Subra for "the mane" in Arabic even though it lies in the lion's paws. It is a blue-white main sequence star with a magnitude of 3.5, and it is about 55 light years distant.
A group of stars that used to be considered part of Leo, ie the tuft of his tail, were made their own constellation in 240 BC by Ptolemy III. These stars are the Coma Berenices and more on them later. The star Wolf359 in Leo is one of the closest stars to Earth, about 7.7 light years distant.
Molly Note: Molly's dim little feline mind has come up with the realization that when she refers to the stars in constellations that she is exploring that many may not be familiar with the Greek alphabet as she is (it's standard scientific usage and Molly has also visited Greece and learned "a little" of the language). So...if you wonder what the alphas and omicrons mean you can look it up on the Wikipedia site about this matter or, for a simpler and more convenient explanation go to this site about the Greek language.

3 comments:

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