Hobbies And Interests
Distance and Time
Light has a finite velocity, traveling at 186,000 miles per second, or about 6 trillion miles per year. This presents a perplexing fact. The light that reaches us from distant stars gives us information only about the state of the star as it existed when the light departed. For the most distant stars, that is billions of years ago, before the Earth cooled to its present state or was even formed. We have no way of knowing what the state of the star is in our "present." When we look at the stars, we are looking into the past.
Stellar Equilibrium
Each star represents a delicate balance between the energetic processes that produce the light we see and the force of gravitation. Atomic collisions and radiation tend to make the star expand while the force of gravity tends to make it contract. As long as these two forces are in equilibrium, the star remains stable, but when a critical imbalance occurs between these two opposing forces, the star can explode as a supernova, implode into a neutron star, or both. A neutron star is a superdense singularity, and astronomers believe there is one at the center of our galaxy.
The Number of Stars in the Sky
Scientists estimate the number of stars in the universe based on assumptions about the distribution of stars in galaxies. Yale University astronomer Pieter van Dokkum questioned the long-standing assumption that most galaxies have the same composition as our own in a 2010 study published in the scientific journal "Nature." His revised estimate for the number of stars in the sky is triple the previous estimate, or 300 sextillion stars, which is a 3 followed by 20 zeros. If a hypothetical stargazer had started counting the stars at the rate of one per second at the moment the Earth was formed, she would not be halfway done today.
Types of Stars
Stars like the sun are relatively rare in the universe. The most abundant stars are red dwarfs, which are smaller than the sun and don't burn as hot. There are also many that are much larger than the sun and burn hotter, giving off white or blue light. The largest star known as of 2011 is Eta Carinae, with 150 times the mass of the sun. Scientists believe it may soon explode into a supernova bright enough to illuminate our night sky sufficiently for reading. Many star systems have two or more stars revolving around each other. These binary systems are probably more common than single stars.