Space Science: Sun As A Star (1970)

I [Music] the sun is our nearest star the only star we can see is more than just a point of Light how do we learn about the Sun at solar observatories astronomers direct their mirrors at the [Music] S they catch its light and send it into their Laboratories for study [Music] the angular diameter of the sun can be measured when that information is combined with the sun's mean distance astronomers can calculate its linear diameter approximately 864,000 mil by calculating its surface area and measuring the amount of energy it gives off the surface temperature of the Sun can be found about 5800 de Kelvin or about 10,000 de F how does our sun compare with other stars this is a diagram which plots the brightness of a star with the Sun as a standard against a star's color which is a measure of its temperature the color ranges from the hottest type O Stars which are blue through the various colors to the coolest Type M Stars which are red the vertical scale shows brightness in terms of the Sun from 1 millionth the sun's brightness to a million times the sun's brightness this kind of diagram which is called a herzsprung Russell or HR diagram for the two astronomers who developed it independently sets the Sun as the standard of brightness the sun is a yellow star spectral type G astronomers found that nearly all stars plotted on an HR diagram lie within this narrow band called the main sequence in main sequence stars there is a definite relationship between surface temperature and brightness as well as between size and Mass Sirius the brightest star to the naked eye is a main sequence star Sirius is hotter than the Sun and brighter it is also larger with about 1 and 1/2 times the Sun's diameter this chart doesn't show relative distances between Stars it simply Compares temperature and brightness wolf 359 at the bottom of the main sequence is cooler than the Sun and dimmer it is a small red star about half the temperature and diameter of the Sun most stars seem to be red dwarfs like wolf 359 but not all stars are main sequence Stars One such star that is not on the main sequence is Sirius b a white dwarf most white dwarfs are hotter than the sun but since their total energy output is much less than the sun's their size must be very small even smaller than the Earth but up here on the HR diagram in the region of the Giants we find yellow stars like capella and red stars like Urus they're not on the main sequence because they give off more light than their temperatures indicate they should this discrepancy is a clue to their large size we can't show the super giant beetlejus to scale on this chart it's more than 2,000 times larger than the sun in diameter to this scale with the Sun a dis 2 in in diameter bejw would be far larger than the entire chart to the same scale as the twoin sun beetle juw is more than 350 ft in diameter but even with its great size Beetle juw has only about 10 times the mass of the sun most stars astronomers have observed have masses between 1/10th and five times that of our sun compared with most of these Stars our sun is a giant so there are differences in size and mass brightness and temperature of stars what about composition the materials a star is made of Clues to the sun's composition come from its Spectrum when the light of the sun is pass passed into a spectrograph The Familiar pattern can be studied Spectra of the sun and stars are usually not photographed in color because it's the black lines that give astronomers the information thereafter the lines are Clues to the chemical elements in Stars probably all of the elements that occur naturally on Earth are present in our sun although only about 70% of them have been identified so far at the surface of the Sun about 90% of the atoms are hydrogen and almost all the rest are helium only a very small proportion are of the heavier elements when the light from other stars is analyzed their Spectra reveal that the composition of most of them is about the same hydrogen and helium are the two main constituents of All Stars the Stars like our sun are great spheres of gas at very high temperature what else do we know about the sun we know that the sun rotates by following the movement of surface features like sunspots astronomers have determined the sun's speed of rotation because the sun is not a solid but a gas actually in the plasma State different parts of it rotate at different speeds at the Equator the period of rotation is 25 days here the period of rotation is fastest halfway to the poles the period is nearly 28 days and at the poles periods of more than 30 days have been reported the sun's period of rotation can also be measured by means of spectroscopic studies of its light Spectra of other stars indicate that they probably rotate much as the sun does the light and other radiation of the Stars which give us all our information about them are the result of a tremendous outpouring of energy the energy comes from nuclear processes that mainly take place deep within the core of the star at temperatures perhaps as high as 25 million de fahren hydrogen atoms are changed into helium atoms by the process we call Fusion we can explain the fusion reaction in a simplified way like this we begin with two protons each one is the nucleus of a hydrogen atom the protons fuse and produce a hydrogen 2 nucleus heavy hydrogen or dyum a positron is given off when the positron is annihilated by an electron energy is the result in the form of gamma rays when the H2 nucleus collides with another proton a nucleus of helium 3 is formed and there is another burst of radiant energy these are also gamma rays when two helium 3 nuclei Collide they produce a nucleus of helium 4 this releases two protons and the cycle can start again it's called the proton proton cycle in the process mass is converted to energy the proton proton cycle produces energy in Stars whose masses are about the same as the sun or less in more massive stars a carbon nitrogen cycle occurs a carbon 12 nucleus absorbs a proton and changes to a nucleus of nitrogen 13 gamma rays are given off the nitrogen 13 is unstable and changes to carbon 13 collision with another proton changes it to nitrogen 14 and releases gamma raay another proton Collision changes it to oxygen 15 with more gamma rays given off oxygen 15 is unstable and becomes nitrogen 15 one more proton Collision splits the nitrogen 15 nucleus into a helium nucleus and a carbon 12 nucleus gamma rays are again given off and the carbon nitrogen cycle can begin again so in all Stars hydrogen is gradually converted to helium with the release of tremendous amounts of energy the life story of A Star is essentially a story of this continuous transmutation of hydrogen to helium a star like the sun begins as a cloud of hydrogen gas like the dark Horsehead nebula in the constellation Orion as gravitational forces shrink the cloud potential energy is released in increasing amounts of radiant energy and the cloud begins to Glow like the great nebula in Orion now the interior density and temperature increase until conditions are right for nuclear reactions to begin and A Star is Born these are young stars in the pleades group perhaps less than 100 million years old the glow around them is probably the remains of the gases from which they were formed at this time of its life a young star is on the main sequence like our sun it's believed that our sun has been main sequence star for about 5 billion years astronomers estimate that it will take another 5 billion years for most of the hydrogen in its core to be converted to helium with this change in composition a star increases in size and brightness and becomes a red giant only to shrink in the course of millions of years into a white dwarf in this form a star dies some Stars end their lives more spectacularly The Crab Nebula was formed by an exploding star a supernova at its Center is a pulsar a tiny rapidly rotating pulsating star believed to be the remains of that cataclysmic event astronomers believe the Ring Nebula was formed from an exploding star a nova or supernova they think the same might be true of the dumbbell nebula and the veil nebula exploding stars are Rarities in the universe more commonly a star's life takes it from gas cloud onto the main sequence then into a red giant and then to a white dwarf our son is a middle-aged ordinary star not much different from billions of other stars in the universe but it is the only one we can study relatively closely and the one on which life on Earth depends all [Music]