Unseen World!

Sirius also known as the Dog Star is the brightest star (−1.46^m) in the night sky. This star can be seen from every inhabited region of the Earth’s surface and, in the northern hemisphere, is known as a vertex of the Winter Triangle. At a distance of 8.6 light years, Sirius is also one of the nearest stars to Earth. It is a main sequence star of spectral type A0 or A1 and has a mass about 2.4 times that of the Sun.

In 1841 Friedrich Wilhelm Bessel deduced that Sirius was actually a binary star. In 1862 Alvan Graham Clark discovered the companion, which is called Sirius B, or affectionately "the Pup". The visible star is now sometimes known as Sirius A. The two stars orbit each other with a separation of about 20 AU and a period of close to 50 years. In 1915 astronomers at the Mount Wilson Observatory discovered that Sirius B was a white dwarf, the first to be discovered. Interestingly, this means that Sirius B must have originally been the much more massive of the two, since it has already evolved off the main sequence.

Historically, many cultures have attached special significance to Sirius. Sirius was worshipped in the valley of the Nile long before Rome was founded, and many ancient Egyptian temples were constructed oriented so that light from the star could penetrate to their inner altars. The Egyptians based their calendar on the heliacal rising of Sirius, which occurred just before the annual flooding of the Nile and the Summer solstice. In Greek mythology, Orion’s dog became Sirius. The Greeks also associated Sirius with the heat of summer: the name Sirius is derived from Seirios meaning "the scorcher". This also explains the phrase "dog days of summer".

There are a few unsolved mysteries regarding Sirius. Firstly, it has been suggested that there is a third very small companion star, but it appears that this has not yet been definitely confirmed. Secondly, ancient observations of Sirius describe it as a red star, when today Sirius A is bluish white. The possibility that stellar evolution of either Sirius A or Sirius B could be responsible for this discrepancy is rejected by astronomers on the grounds that the timescale of thousands of years is too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place. Alternative explanations are either that the description as red is a poetic metaphor for ill fortune, or that the dramatic scintillations of the star when it was observed rising left the viewer with the impression that it was red. A third mystery is a suggestion that the Dogon tribe of Africa knew about unseen companion star(s) before they were discovered in the 19th century, although careful research reveals this was probably cultural contamination on the part of visiting astronomers who went to the region to observe a transit of Venus. This is a source of speculation for UFO enthusiasts and was the subject of the book The Sirius Mystery by Robert Temple.

Some facts about Sirius A

• Parallax: 0.379 arcsecs
• Spectral type: A1 V
• Radial velocity: −9 km/s
• Proper motion: 1.339 arcsecs/year
• Apparent visual magnitude: −1.44
• Absolute visual magnitude: 1.45
• Luminosity: 26.1 Solar Luminosities

Some facts about Sirius B

• Parallax: 0.379 arcsecs
• Spectral type: White dwarf
• Radial velocity: −9 km/s
• Proper motion: 1.339 arcsecs/year
• Apparent visual magnitude: 8.44
• Absolute visual magnitude: 11.3
• Luminosity: 2.4e−4 solar luminosities
• Surface temperature: 25000K

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The Hubble Deep Field (HDF) is an image of a small region of the sky, based on the results of a series of observations by the Hubble Space Telescope.

The field is so small that only a few foreground stars in the Milky Way lie within it; thus, almost all of the 3,000 objects in the image are galaxies, some of which are among the youngest and most distant known.

By revealing such large numbers of very young galaxies, the HDF has become a landmark image in the study of the early universe, and it has been the source of almost 400 scientific papers since it was created..

Then came along “The Hubble Ultra Deep Field”

Here’s a new way to appreciate the Hubble Ultra Deep Field image, by flying through the 10,000 galaxies in this deepest of all Hubble images. Watch the whole video if you need the background on the Hubble Deep Field and subsequent Ultra Deep Field. Start at about 3:00 if you just want to see the distances between the galaxies in this image. Nice

For more information click here

Supergiants are the most massive stars.

Supergiants can have masses from 10 to 70 solar masses and brightness from 30,000 up to hundreds of thousands times the solar luminosity.

They vary greatly in radii, usually from 30 to 500, or even in excess of 1000 solar radii.

Because of their extreme masses they have short lifespans of only 10 to 50 million years and are only observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies.

They are less abundant in spiral galaxy bulges, and are not observed in elliptical galaxies, or globular clusters, all of which are believed to be composed of old stars.

Currently, the largest known stars in terms of physical size, not mass or luminosity, are the supergiants VV Cephei, V354 Cephei, KW Sagitarii, KY Cygni, and the Garnet Star..

For more information about the topic Supergiant, read the full article at Wikipedia.org

The ancient Greeks called our galaxy the Milky Way because they thought it was made from drops of milk from the breasts of the Greek goddess Hera.
Yuri Gagarin survived the first manned spaceflight but was killed in a plane crash seven years later.
Astronauts become a little taller in space. There is less gravity, so their bones are less squashed together.
Astronauts’ footprints and Lunar Rover tyre tracks will stay on the moon for millions of years as there is no wind to blow them away.
About 1500 stars are visible at night with the naked eye in a clear, dark sky. There are 88 constellations altogether. The smallest star measures about 1700 km across. It is a white dwarf called LP 327-16.
The first object to orbit earth was Sputnik 1, launched by the USSR in October 1957.
The first animal in space was the Soviet dog, Laika, in November 1957. It died on the flight.
The first animals to survive in orbital spaceflight were the Soviet dogs, Strelka and Belka, launched in Sputnik 5 in August 1960.
The first person to orbit earth was Yuri Gagarin, from the USSR, in April 1961.
The first American to orbit earth was John Glenn in February 1962.
The first woman in space was Valentina Tereshkova, from the USSR, in June 1963.
The first person to walk on the moon was Neil Armstrong in July 1969. (HMM…..THIS HAS TO BE RESEARCHED)