By Zaina Berger

Introduction to Stars:

Stars are huge balls of gas that you can only see at night time. Some are bigger than others. Most stars are the same size as the sun. During the beginning of stars’ life they contain about 2/3 hydrogen and 1/3 helium. The birth of stars is a cloud of gas that collapses until in the center pressure and temperatures are high enough to start the nuclear fusion. The cloud begins to shine, first due to the set free gravitational energy ( the energy associated with the model used within physics to explain how gravity exists in the universe), later, because of the nuclear fusion (the process by which multiple like charged atomic nuclei join together to form a heavier nucleus) Therefore, a star is born. Main sequence stars happen when fusions hydrogen transfers to the helium in its core. This happens for the most part of a stars life.

Nuclear fusion: fusions hydrogen:

Stars during the day!

Stars do glow during the day, but we can't see them because of the glare of sunlight. When the sun is up, the blue color in sunlight gets scattered all over the atmosphere, turning the sky to the blue color. This blue light is much brighter than the faint light coming from the stars, so it prevents us from seeing them. If you were standing on the Moon, for instance, where there is no atmosphere, you would see the stars both day and night.

Different Colored Stars

  There are different colors for every star. You can

conclude its mass, size, and luminosity. For example, red stars are small and cool, blue stars

are big and hot, and orange, yellow, and white are in between.

Blue stars!

Blue stars have more than three and up to 150 solar masses. When a star shines blue it is because the star is bigger and hotter which is more intensive. These stars burn their fuel much quicker than smaller stars and for this are much more luminous.

Red Stars!

Red stars or “red dwarf” live very long, billions of years! They are the most frequent and numerous types of stars. They have a small mass and have relatively low temperatures in their cores and energy generates at a slow rate. Even the largest red star has only 10% of the sun’s luminosity.

Orange,yellow,white stars! Orange, yellow, and white stars have ¾ solar mass

a star shines orange, with three times it is white. The surface temperature varies according to this between 4000 and 10000 Kelvin. Our Sun has 5770 Kelvin and therefore is yellow. The life span of such stars ranges from one to several billion years, the bigger the less. A fun fact is our Sun will live about 10 billion years, 4.6 it has already behind!

Lifespan of a star

Lifespan of a star is determined by its mass. Stars spend 80% of their life on the main sequence. The first sign of old age is a swelling and reddening of its outer regions. When all of the fuel has been exhausted, a star generates sufficient pressure at its center to balance the crushing force of gravity. This happens to small stars. The star collapse under the force of its own weight. When a star collapse its life ends. It is called a white dwarf and is said the sun will end its life this way. For large stars, its final collapse generates a violent explosion, blowing the innards of the stars into space.

Black holes in Stars:

Once a star dies a black hole has formed, all its mass is squeezed into a singular point, both space and time stops. At the center of the black hole mass has no volume and time does not pass. Nobody knows why space and time stops.

Space-time in black holes can be thought of as an elastic sheet that bends under the weight of objects placed upon it. The more massive the object, the more space-time bends. If the massive object is also spinning, it causes space-time to not only bend but to twist as well. Scientists call this effect “frame dragging." Space-time will cause gas falling into a black hole to move in certain ways.

Tools astronomers can use! The earliest people studied the stars with just their eyes, but today we can study

the universe with everything from binoculars to super strong telescopes. When Galileo turned the first telescope toward the skies, he was able to see craters on the moon, dark spots on the surface of the Sun, tiny moons moving around Jupiter. No one else had ever seen these things. Light from planets, stars and galaxies "rains down" on Earth, and a telescope collects this light and lets us look at the object the light came from. Some telescopes, called refracting telescopes, collect and focus light through a glass lens. Another type, the reflecting telescopes, reflect light on a glass mirror. The bigger the telescope the more light it collects, giving us a better view of what we want to look at. The Keck in Hawaii is the world's largest optical telescope. It doesn't have just one big mirror; it has 36 little mirrors. With the help of a computer, these little mirrors work together like one big 10-meter mirror. The refracting and reflecting telescopes collect and focus visible light, which is light that we can see. There are also other types of light that we cannot see. Astronomers have built many different types of telescopes to look at all the different types of light. On Earth we can look at visible light and radio waves. Some of the very largest telescopes are radio telescopes, like the VLA in New Mexico. Other types of light, like X-ray light and ultraviolet light can only be looked at from space, so astronomers have built telescopes in space that orbit the Earth.

New vocabulary!

Nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus.

The solar mass is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies.

how to find solar mass = 1.98892 × 1030 kilogramsThe main sequence is a continuous and distinctive band of stars that appear on plots of stellar color versus brightness.

Citations:

"A star is born." star life cycle. 1994. 4 Feb 2009 <http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html>.

"The Life Cycle of stars." The Life cycle of stars. 1988. 4 Feb 2009 <http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/LC_main3.html>