Stars seem to twinkle because we see them through the layers of the Earth‘s atmosphere As Light Passes through these layers,it is distorted so that the amount we actually see changes constantly.The star nearest the horrizon appear to twinkle the most because the light is passing through a greater depth of atmosphere.Stars don’t twinkle when viewed from space,which is why telescopes in space,such as the hubble give the best possible view of distant stars and galaxies.
A star is a luminous body of gas,mostly hydrogen and helium.Stars generate light, which makes it possible for us to see them with a telescope or the naked eye.They also release energy from nuclear fission reactions in their core.
Not counting the sun,The brightest star as seen from Earth is Sirious,Known as the dog star,in the constellation of Canis Major.It has a diameter of 149,598,020 km and is more than 24 times brighter than the sun.The Star Cygnus OB2 No 12 ,discovered in 1992,is so far away that,it can not be seen from earth .It may be the brightest star in the galaxy – upto six million times as bright as our Sun.
HDE 269810 is a star in the large Magellanic Cloud – 170,000 light years from earth( a light year is the distance light travell in a year).It has been discovered by the Hopkins Ultraviolet Telescope to be 190 times as heavy as our Sun.
The Largest star is the M-class supergiant betelgeuse,or Alpha Orionis.It is the top left Star in the in the Constellation of Orion which is 310 Km light years away .It has a diameter of 700 million km ,which is about 500 times greater than that of the sun.
Proxima Centauri,discovered in 1915,is 4.22 light years from earth.A spaceship moving at 40,000km/h – which is faster than any human has yet travelled in space – would take more than 114,000 years to reach it.
These are vast explosions in which a whole star is blown up.They are extremely bright ,revalling for a few days the combined light output of all the stars in the galaxy.Supernovae are rare – the last one in our galaxy was seen in 1604 by the german astronomer Johannes Kepler.
Quasars are extremely distant ratio galaxies – Galaxies giving out large amount of radio energy – and the brightest objects in the universe .Even those near the most distant edge of the observable universe are easily detected by small radio telescopes.The radio emission is typically 1000000 to 100000000 times greater than that of normal galaxy,& they are bright as or brighter than the brightest radio galaxies.
A Black hole is a star that has collapsed into itself.It has a Surface Gravity So Powerfull that nothing can escape from within it.
Galaxies are groups of billions of stars that are held together by the force of gravity .Most galaxies are either spiral or elliptical,but some are irregular in shape.
The Milky Way :
The Best Known Galaxy is the Milky Way.The word Galaxy itself comes from the greek word for milk.This is because before Telescopes were powerful enough to prove that they were made up of individual stars ,galaxies looked like milky or cloudy areas in the sky.Our relatively known solar system is only of 100 to 200 billion Stars in the Milky Way Galaxy,which 100000 light years in diameters.The Sun and the Planets take about 200000000 years to complete one orbit around its Center.
The Large Magellanic Cloud,which is visible only in the southern hemisphere,is 170000 light years from earth and 39000 light years in diameter.
The Central galaxy of the Abell 2029 galaxy cluster was discovered in 1990.It is 1070 million light years distant and has a diameter of 5.6 million light years,80 times the diameter of our on galaxy.It has a total light output equivalent to 2 trillion times that of the Sun.
The Sagittarious Dwarf discovered in1994 is more than 70000 light years from earth and is being torn apart.
Remotest visible object
The Most distant thing in the universe that can be seen with the naked eye is the Andromeda Galaxy,which 2309000 light years from earth.This Galaxy has 300 billion stars and a diameter of 180000 light years.The light we see now from Andromeda left there just after the first human appeared on earth.
Most Distant Galaxy
In 2004,astronomers at the europian southern Observatory,Chile Announced the Discovery of Galaxy Abell 135 IR1916.It exists an astonishing 13.2 billion light years from earth.