Sunday, February 18, 2007
Menkalinen, beta Aur, is also a spectroscopic binary. Within just four days the stars complete their revolution much faster than those of alpha Aur. Since they are eclipsing each other the brightness of beta Aur seems to vary.
The eclipsing binary epsilon Aur has an extraordinary long period; every 27.1 years the brightness varies from 3.0 mag down to 3.8 mag as the brighter component is then eclipsed by the darker companion. This eclipse lasts a full year (the last eclipse took place in 1983). Calulations show that the dark component of epsilon Aur has about 10 -12 solar masses. Because of its small size it is a good candidate for a black hole; unfortunately this conflicts with the observed lost of brightness during the eclipse. According to studies of Wilson and Cameron the solution is a ring of obscuring material which surrounds the black hole. (There is still doubt that the companion is a black hole; a star which a 10 times smaller brightness would fit the model, too.)
Another eclipsing binary is zeta Aur; a K4 bright giant and a B8 main sequence star revolve each other every 2 2/3 years.
The double omega Aur can be viewed with small telescopes; it consists of a 5th mag and a 8th mag companion.
Telescopes with an aperture of at least 100mm and a high magnification are required to split the tight double theta Aur. An A0psi star of 2.62 mag is accompanied by a star of 7th mag.
The planetary nebula NGC(*) 2149 (the asterisk indicates that this object can be found in the NGC supplementary catalogs of J.L.E. Dreyer) appears as a small oval ring of 10th mag.
The diffuse nebula I 405 is also called Flaming Star.
I 410 consists of a cluster with an nebulosity attached.
There a several open clusters in this constellations.
About 60 members belong to M36. Its a good object for the use of binoculars. A beautiful group of stars is M38 showing an oval shape. The richest of these three Messier objects is M37. It contains about 150 stars with magnitudes of 12.5 and brighter and about 500 in total. Detailed information about all three Messier objects can be found in the Messier database.
The meteor shower of the Aurigids is generally observable between January, 31st, and February, 23rd. This shower is known for its bright fireballs.
From August, 25th, till September 6th, the shower of the Alpha Aurigids is active. Although the annual maximum is about 9 meteors, outbursts of up to 30 were observed in 1935 and 1986.
Thursday, February 08, 2007
A constellation, which is the head of a constellation family, located in the equatorial region of the sky and belongs certainly to the most famous constellations. It extends from RA=4h 40m to RA=6h 20m and DECL=+23 degrees to DECL=+8 degrees.
In some ways the central part of this constellation reminds on a oblique sand-glass. In wintertime Orion is a magnificent constellation which can easily be found by the the three stars forming a line building the belt of the Hunter. The belt stars point towards Sirius, the brightest star in the constellation of the Larger Dog, Canis Major, situated SE of Orion.
From his belt there hangs a well defined deggar, which is known for one of the most famous nebulas in the sky: The Large Orion Nebula (M42).
Orion lies close enough to the Milky Way to be interesting enough to be swept even with low-power telescopes or binoculars.
Additionally to the data given above there is a skychart to locate the stars and objects.
Stars and objects
The shoulder star alpha Ori, Betelgeuse, is a variable red giant; its brightness varies from 0.4 mag to 1.3 mag with no set period. It belong to the 20 brightest stars in the sky. During it pulsations the diameter of the star varies from 300 to 400 times the diameter of the sun.
The leg of the hunter, beta Ori, Rigel (arab.: the foot), is a blue-white giant of 0.08 mag. This makes it the sixth brightest star in the sky and the brightest in the constellation Orion. With medium sized telescopes it is possible to distinguish the companion of Rigel, a 7th mag star (smaller telescopes may fail to reveal the companion because of the glare of Rigel).
This constellation offers a great number of binaries and multiple stars:
For binoculars and smaller telescopes the following stars are of interest:
Next to it lies theta2 Ori, a duo of a 5th and a 6th mag star.
For resolving the tight double of zeta Ori (Alnitak) in its consisting parts, a bright star of 2.02 mag and a 4th mag companion, scopes with an apertur of at least 75mm and a high resolution are required. Further more there is a wider companion of 10th mag.
Eta Ori is a difficult pair. Scopes with an aperture of 100 mm and higher are necessary to split it into its 4th mag and 5th mag stars.
The constellation Orion became most famous for its nebula. The Messier database has detailed information about The Large Orion Nebula M 42 and M 43, the DeMairan nebula, which is a part of the Orion Nebula.
Around October 21 each year the famous Orionid meteor shower reaches its peak. Coming from the the border to the constellation gemini as much as 20 meteors per hour can be seen. More information about this meteor shower and the Chi Orionids, which are active around the beginning of december can be found in the meteor shower calendar by Gary Kronk. (Readers in the US might use the original site of Gary Kronk).
According to greek mythology Orion died being stung by a scorpion. He is set such in the sky that he sets in the west while his slayer, the Scorpius raises in the east.
Followed by his two dogs he is now fighting the bull Taurus.
According to Secrets of the Night Sky (Bob Berman, William Morrow &Co, 1995) the ancient Sumerians saw in this star pattern a sheep. The name Betelgeuse literally means "the armpit"; in case of the Sumerians it meant "the armpit of the sheep."