Stars are the most basic entity within the universe, for they are present to varying degrees in galaxies, nebulae, open
and closed clusters as well as supernova remnants. They have graced the evening sky ever since man first started becoming
aware of his existence and have been intricately intertwined in culture, religion, superstition and many facets of human
behaviour.
Our galaxy is believed to contain 300 billion (3x108) stars
whereas over 70 sextillion (7x1022) stars are believed to exist within the universe. The greatest accumulation
of stars is in the form of galaxies where hundreds of billions
of stars form these island universes. Less populous but still large accumulations of stars are observed in
globular clusters where up to one million stars are
strongly held together gravitationally (approximately 150 such clusters exist in our galaxy).
Open clusters also involve a collection of stars (usually in
the hundreds) which are weakly held gravitationally and are more frequent than globular clusters (at least 1500 open
clusters exist in our galaxy).
The Sun (Sol) is, of course, the closest star to our planet lying at a
distance of approximately 150 million kilometers away. Sol is 4.6 billion years old and approximately halfway through its
10 billion year lifespan. It is characterized as a yellow dwarf of spectral type G2V and with a surface temperature
between 5,500 and 6,000 degrees Kelvin. With a diameter of 1.4 million kilometers (109 times that of earth), it is
considered average in size. Sol lies 26,000 light-years away from our galaxy's core and requires between 225 and 250
million years to make one complete revolution around the same core. Aside from being the brightest object in our skies,
its motion during the course of a year fluctuates in both azimuth and altitude forming a figure-eight shape commonly
referred to as the analemma.
Proper Star Name: N/A Bayer Letter: ä Cephei Tycho Catalog: TYC 3995-1479-1 Henry Draper Number: HD 213306 Luminosity 1639 + 524 x Sun Distance: 982 + 146 light-yrs RA / Dec: 22h 29m 10s / +58° 24' 55" B-V Color Index: +0.757 Radial Velocity: -16.6 km/sec Magnitude (Visual): 4.13 |
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Date: Nov 21, 2009 19:35 - 20:20 UT+2 Location: Athens, Greece Equipment: AP 160/f7.5 Starfire EDF AP 1200GTO GEM SBIG ST-2000XM SBIG CFW-8A SBIG LRGB filters Integrations:
Image Scale: 1.27" per pixel Temperatures:
Software: CCDSoft V5.00.188 CCDStack V1.6.0.5 Photoshop CS2 |