AMATEUR ASTRONOMY:

THE PERSEIDS ARE COMING- THE CONSTELLATION PERSEUS:

THE CONSTELLATION PERSEUS:
In most years the Perseid meteor shower is the most spectacular of the many meteor showers observable. There are usually between 50 and 80 meteors per hour on the night of its peak which this year falls in the early hours of Tuesday, August 12. Here's a little introduction to the constellation Perseus from which these meteors seem to originate.
FINDING PERSEUS:
The exact location of any constellation varies, of course, with the season and the time of night. Perseus, however, is a circumpolar constellation, and one can locate it easily by reference to other northern sky landmarks. At this time of year it can be found in the northeast;the later at night the higher it will be seen. Draw a line from the two "pointer stars" of the Big Dipper, Dubhe and Merak, across the Polaris the North Star. Continue the line onward past the inverted pentagon of Cepheus to the "W" of Cassiopeia. Look down towards the horizon, and you'll find the "K" of Perseus.
If this is not helpful there are a number of star maps online that can help you in locating any of the constellations. See:
Your Sky
The Dome of the Sky
and for a selection of many sky maps, some free and some not, go to Planetarium Software.

THE STARS OF PERSEUS:
The diagram to the left above illustrates the major stars of Perseus. Molly has always seen Perseus as the "K" shape described by most commentators. Others have described it as a "fleur de lis", but I have consistently been unable to see such a thing in this constellation. Perseus contains four named stars. The brightest, alpha-Per, is usually called Mirfak, from the Arabic for elbow, and sometimes Algenib, from the Arabic for "the side" (though other stars also bear this name). It is a white supergiant of 1.8 apparent magnitude and is about 620 light years (lys) away. Mirfak is 62 times the size of our sun and 5,000 times as bright.

The most famous star in Perseus is beta-Per, Algol the demon star. The name comes from the Arabic "Alghul" which means "the ghoul" or "the demon". It is often referred to as "the head of the demon" because it is supposed to represent the head of Medusa (see 'The Legend of Perseus' later in this blog). This star is the classic eclipsing binary variable star. In these systems each member of the pair periodically eclipses the other. Algol consists of a blue main sequence star and a yellow-white subgiant. This system usually shines with a magnitude of 2.1, but every 2.87 days it dims to magnitude 3.4 for 10 hours as the subgiant passes in front of the other star. this system is 105 light years away.

Xi-Per is called Menkib from the Arabic for "shoulder". It is a blue star of magnitude 4 with a distance of 150 light years. Omicron-Per is called Atik from the Arabic for "collarbone". It is a blue giant of magnitude 3.8 and is 1,000 light years away.

Epsilon-Per (to the horizon from Mirfak and to the west of Algol) is the main radiant of the Perseid meteor showers. Note that the first diagram above is incorrect in this matter, though the casual observer could hardly tell the difference. There are also, however, other radiants within the constellation, and so not all the meteors seen will be traceable back to the neighbourhood of epsilon-Per. Epsilon-Per is a binary system about 130 lys from Earth. the brighter component is a blue main sequence star of magnitude 2.9, and the dimmer is only of the 8th magnitude. Stars dimmer than magnitude 6 are invisible to the naked eye.

THE PERSEIDS ARE COMING:

AUGUST 12TH/13TH:

THE CONSTELLATION PERSEUS:

In most years the Perseid meteor shower is the most spectacular of the many meteor showers observable. There are usually between 50 and 80 meteors per hour on the night of its peak which this year falls on Sunday August 12 and Monday August 13. Here's a little introduction to the constellation Perseus from which these meteors seem to originate.

FINDING PERSEUS:

The exact location of any constellation varies, of course, with the season and the time of night. Perseus, however, is a circumpolar constellation, and one can locate it easily by reference to other northern sky landmarks. At this time of year it can be found in the northeast;the later at night the higher it will be seen. Draw a line from the two "pointer stars" of the Big Dipper, Dubhe and Merak, across the Polaris the North Star. Continue the line onward past the inverted pentagon of Cepheus to the "W" of Cassiopeia. Look down towards the horizon, and you'll find the "K" of Perseus. The above diagram shows the nearby constellations and the radiant (the apparent origin of the Perseid meteors). If you observe late enough at night(best just before dawn) you will also see the planet Mars beneath Perseus towards the horizon.

If this is not helpful there are a number of star maps online that can help you in locating any of the constellations. See:

Your Sky

The Dome of the Sky

and for a selection of many sky maps, some free and some not, go to Planetarium Software.

THE STARS OF PERSEUS:

The diagram to the left illustrates the major stars of Perseus. Molly has always seen Perseus as the "K" shape described by most commentators. Others have described it as a "fleur de lis", but I have consistently been unable to see such a thing in this constellation. Perseus contains four named stars. The brightest, alpha-Per, is usually called Mirfak, from the Arabic for elbow, and sometimes Algenib, from the Arabic for "the side" (though other stars also bear this name). It is a white supergiant of 1.8 apparent magnitude and is about 620 light years (lys) away. Mirfak is 62 times the size of our sun and 5,000 times as bright.

The most famous star in Perseus is beta-Per, Algol the demon star. The name comes from the Arabic "Alghul" which means "the ghoul" or "the demon". It is often referred to as "the head of the demon" because it is supposed to represent the head of Medusa (see 'The Legend of Perseus' later in this blog). This star is the classic eclipsing binary variable star. In these systems each member of the pair periodically eclipses the other. Algol consists of a blue main sequence star and a yellow-white subgiant. This system usually shines with a magnitude of 2.1, but every 2.87 days it dims to magnitude 3.4 for 10 hours as the subgiant passes in front of the other star. this system is 105 light years away.

Xi-Per is called Menkib from the Arabic for "shoulder". It is a blue star of magnitude 4 with a distance of 150 light years. Omicron-Per is called Atik from the Arabic for "collarbone". It is a blue giant of magnitude 3.8 and is 1,000 light years away.

Epsilon-Per (to the horizon from Mirfak and to the west of Algol) is the main radiant of the Perseid meteor showers. Note that the first diagram above is incorrect in this matter, though the casual observer could hardly tell the difference. There are also, however, other radiants within the constellation, and so not all the meteors seen will be traceable back to the neighbourhood of epsilon-Per. Epsilon-Per is a binary system about 130 lys from Earth. the brighter component is a blue main sequence star of magnitude 2.9, and the dimmer is only of the 8th magnitude. Stars dimmer than magnitude 6 are invisible to the naked eye.

COMING SOON:

THE LEGEND OF PERSEUS

THE PERSEID METEOR SHOWER

Stay tuned tomorrow.

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.

THE CONSTELLATION HYDRA:

Hydra is the largest modern constellation but one of the least recognized ones. It is visible this time of year stretching from Cancer in the west to Libra in the east. It takes almost six hours to fully rise. Throughout its course it lays just south of the ecliptic and spans four of the zodiacal constellations. Its only bright star is Alphard which lays just south and a little to the east of the easily visible Regulus in Leo. Alphard (alpha Hydra) is giant orange star of apparent magnitude 2.0, and it is about 85 light years distant. It is from the Arabic and means "the solitary one".

Hydra was one of the 48 constellations recognized by Ptolemy, and its most common mythological reference is to the Hydra of Lerna that Heracles slew as one of his twelve labours. The lair of this water snake was beneath the lake of Lerna in the Argolid where it was reputed to guard an entrance to the underworld. The Hydra was reputedly one of the children of Typhon and Echidna, giants who waged war against the gods of Olympus. Its siblings were the Nemean Lion, the Chimaera and Cerebus. Like Cerebus Hydra was a multi-headed monster who grew two heads back for every one cut off. Heracles was stymied until he asked his nephew Iolaus for help. Iolaus came up with the idea of cauterizing each stump as the head was cut off, thus preventing regrowth. One of the heads, however, was immortal. When Heracles cut that one off he placed the still living head under a great rock where it could do no harm. When Heracles returned to Eurystheus, an agent of Hera who hated Heracles, who had assigned him his labours Eurystheus declared that the help of Iolaus made this labour invalid. Heracles used the poisonous blood from the Hydra applied to an arrow to kill the centaur Nessus as another one of his labours. It was the tainted blood from Nessus' cloak that eventually killed Heracles.

Another version of the origin of Hydra says that Apollo sent his servant the crow (the constellation Corvus) to fetch water in a cup (the constellation Crater), but the crow dallied lazily and brought back the water snake Hydra in the cup as an excuse. Apollo angrily threw the three of them into the sky.