Our Sun and the Stars • All stars are suns • Our sun is a star • At any given night, we can see about 2,000 stars • Within a year, we will see over 6,000 stars • With the use of telescopes, you see thousands more
The total amount of stars in our galaxy are in the billions • For example, if our sun was the dot over this “i”, the nearest star would be ten miles away • For these great distances, miles are no longer practical, we use: ‘Light Years’ • the distance it takes light to travel in one year moving at 186,000 miles per second or • about 6 million million miles (6 trillion miles)
At this scale, the nearest star is 4.3 light years away • SIRIUS: the brightest star is 8.8 light years away • Another interesting fact is that in the year 2000, it is known that 30 stars have planets orbiting them. One star (Andromedae) has three planets orbiting around it. • The only way we can truly see and study stars and every thing else in space for that matter, is with the use of telescopes. • TELESCOPES • Invented in 1609 by Galileo Galilei • Today, we have two types of telescopes:
1) Refracting • These are great for viewing objects that have a lot of light (planets and stars)
2) Reflecting • this is better to look at fainter objects (Galaxies) • the largest refracting telescope has a forty (40) inch lens ( located in Yerkes Observatory in Wisconsin ) • the largest reflecting telescope is 200 inches • this can photograph stars 6 million times than the faintest stars we see.
The Sun is the nearest star to Earth. The sun is just an ordinary star. The next brightest star to us is called Alpha Centauri. Light from Alpha Centauri takes 4.3 years to get to us. Light from our sun only takes 8 minutes. Alpha Centauri are really three stars all orbiting each other. One of these stars Proxima Centauri is the closest star to Earth next to our sun. There are many kinds of stars, big and small, close and far, bright and dim, some even change in brightness in a matter of hours (these are called pulsating stars). When most stars get old they bloat and become ‘red giants’. Our sun will eventually run out of fuel and become a red giant. As it gets larger it will engulf the inner planets, possibly the earth as well. It may explode or go ‘Super Nova’. Some times a red giant just runs out of fuel, dims and grows smaller. These type of stars are called ‘White dwarfs’.
The Herzspring-Russel (H-R) diagram illustrates the history of a star. Generally the older the star the greater the luminosity. The sun is an average middle age star. The youngest stars are found in the bottom right called ‘Red Dwarfs, the oldest are the ‘Blue Giants’. Temperature generally increases with age.
Sometimes a massive star explodes and may form a black hole. A black hole comes into being when the gravity of the exploding star is so strong that it squeezes the ‘ash’ of the explosion completely out of existence. It is a hole in space. It is like a trash can, everything nearby is attracted into the black hole never to be seen again, even light is absorbed by the black hole. A Black Hole A Super Nova A Nebulae
The largest cluster of stars are called ‘Galaxies”. They are literally cities of stars. • To the unaided eye they look like faint blurs in the sky, but a telescope reveals that they are made up of thousands of millions of stars. • A typical galaxy contains 100 000 stars. There are about 1 000 000 galaxies in the Universe. The galaxy that our solar system is in is of course the Milky Way. Elliptical Galaxy Irregular Galaxy Spiral Galaxy
The space in between stars is not always empty. It can be made of gas (mostly Hydrogen) and dust. Some of this gas and dust even glows, this is called a ‘Nebulae’. Stars are born deep inside nebulae and dust clouds in space. Gravity pulls the thin gas of the nebula into balls of denser gas. Perhaps the process starts when, quite by chance, a swirl of gas forms that is denser than neighboring gas. The gravity of the dense swirl in turn attracts nearby gas and so a ball of gas forms.
The ball shrinks, pulled inward by its own gravity. Inside the shrinking gas balls - called protostars - the pressure and temperature rise. This happens because all gases get hotter as they are squeezed into a smaller space. Eventually the temperature reaches 10 million degrees centigrade and that starts a nuclear fusion reaction with Hydrogen. A star is born. Some nebulae can even be the remnants of a star that has exploded.
The sun is a giant nuclear furnace. The nuclear reaction that occurs inside the sun is called Fusion (atoms are combined), the opposite of Fission which is the splitting of atoms. Humans have harnessed Fission, but not yet Fusion. • Hydrogen and Helium are the main gases in the Sun’s furnace. • The reason why the sun doesn’t just blow up like a hydrogen bomb is that as the gases expand from the nuclear reaction, gravity takes over and pulls the gases back in. These gases have cooled by now and as they come back in they are reheated and the nuclear reactions occurs again (Convection Currents). The Sun is a balanced nuclear furnace.
The sun is made up of some interesting components: • a) The Photosphere and Sun Spots: the outer surface of the sun is called the Photosphere. It has a temperature of 5 500 degrees Celsius. There are darker patches called sunspots. These are not truly black they are just cooler areas and by contrast appear to be black.
b) Chromoshpere and Solar Flares: The part just above the photosphere is called the chromosphere. It is this sphere that gives the sun the redish colour. The chromopshere is the sun’s atmosphere. Sometimes this atmosphere erupts into violent stomrs sending part of the chromsphere into space. These fire balls are called ‘Prominences or Solar Flares’. A Prominence is usually U shaped and falls back to the sun. A Solar Flare shoots out into space.
c) The Corona: The sun also has an outer atmosphere called the corona. The extreme brightness of the sun hinds the corona. It can only be seen during a Solar Eclipse, which we will talk about when we study the moon.
d) Solar wind: The sun gives off electrically-charged particles called solar wind. It is this solar wind that creates the famous tail on a comet. • The Sun converts 4 million tonnes of mass to energy every second. The sun has enough fuel to burn for another 5 000 million years. • The Sun’s energy production is enough to supply the electrical needs of the USA for 50 million years.
Sunlight • Sunlight is a mixture of colours. • When you pass sunlight through a glass prism the light is refracted (bent) into these mixture of colours called ‘The Spectrum’ • Red Orange Yellow Green Blue Violet • (bent the least) (bent the most) • (long wave lengths) (short wave lengths) • If the spectrum has dark lines running vertical, it tells us that some of the light has been absorbed. These dark lines are called Fraunhofer lines. • If you study these lines you can tell what materials an object, like a planed, is made up of. Later in this course you will see how the study of the spectrum is important to Remote Sensing!
A Rainbow is the spectrum created by water droplets in the sky. • As the sun’s light passes through the atmosphere some of the light is refracted or bent or scattered. Blue rays are scattered the most - that is why the sky is blue. Yellow is scattered the least - that is why the sun looks yellow. • In northern latitudes the atmosphere is so thin that few gasses exist (almost a vacuum). The sun’s rays light up the sky and create the Northern lights or the Aurora Borealis. Northern lights occur after highly charged particles from a recent solar flare or sunspot excite the thin atmosphere. • During certain sunsets and sunrises the sun’s rays are very slanted and can literally bounce off the atmosphere and project an image of the sun higher in the sky. The sun will look distorted and huge and usually very red. “Red sky at night - sailors delight”