Ch23, Light, Astronomical Observations, and the Sun, and Ch 24 Of visible colors
ID: 298445 • Letter: C
Question
Ch23, Light, Astronomical Observations, and the Sun, and Ch 24 Of visible colors, red light has the longest wavelength, understand the Doppler effect/red shift that demonstrates universe is expanding; understand nuclear fusion powers the sun, fusing hydrogen atoms to create helium; Earth is an average sized planet rotating around an average star in a spiral galaxy we call the Milky Way, that contains some 200 billion stars, one of billions of galaxies in the universe; also understand basic 'Big Bang', age of the universe an t e expansion of the universe, (more on red shift) better explained on pages 703 and 704Explanation / Answer
Imagine a car approaching an observer with its siren blasting. The pitch of the siren is initially high and increasing as it approaches the observer. That means the sound frequency is high. But as the car passes her, then suddenly the pitch of the siren seems to be reducing until it disappears. That means the frequency is greatly reduced as the car goes away from the observer. This shift in frequency of any wave, be it sound or light and which is produced by a moving source like a car or a star in the universe is known as Doppler effect.
It was first observed by an Austrian Physicist, Dr. Christian Doppler. Hence the name, The Doppler effect.
This effect is also seen in the universe albeit not in terms of sound but in that of light. Light is composed of a spectrum of colors from blue to red. Blue has the highest frequency and red, the lowest. Now imagine that a star is approaching an observer. In this case, the spectrum of seven colours will experience a shift to the blue region due to the increase in frequency. This is known as Blue-shift. On the other hand, if a star is going away from the observer, the spectrum will experience low frequency and the light would seem to shift towards red. This is known as the red-shift.
Now, from telescopic observations from the earth, it appeared that all the stars are shifting towards red in their spectrums. This suggested that the stars are moving away from the earth and each other i.e, the universe is expanding.
Our sun is composed of 70% Hydrogen and 30% Helium. Its gaseous mass is constantly generating energy due to the process of Nuclear Fusion of Hydrogen atoms. Nuclear fusion is process in which four Hydrogen atoms, under the weight of sun’s gravity, combine to form an atom of Helium. This process leads to release of tremendous energy because the total energy of four hydrogen atoms is greater than the resultant helium atom. This energy, in the form of heat and light is known as Fusion energy. This process takes place mainly in the core of the sun
The Universe is composed of billions of galaxies. Milky way is one of those galaxies having a spiral shaped disk and boasting nearly 200 billion stars. It however is a mid-sized galaxy compared to Andromeda (Diameter = 220,000 light years) that is almost twice the size of milky way and having an estimated stars in the range of 400-800 billion.
Our solar system is located 25,000 lightyears inside from the outer rim of the Milky way. Our sun is an averaged sized star belonging to the main sequence of H-R diagram. There are many other stars like Red giants and Supergiants that are over 100 times massive than the sun and there are also some stars like the White dwarfs that are only 1/10th the size of the sun.
Our Earth is an average sized planet compared to giants like Jupiter and Saturn at one end and dwarfs like Mercury.
According to the Big Bang theory, the Universe began as a point of singularity that was incredibly hot and dense. Around 13.7 billion years ago from now, this point exploded and thus began the process of the formation of heavenly bodies like nebulae, galaxies, stars and planets. With the help of Red-shift, Prof. Edwin Hubble was successful to identify the fact that the universe was indeed expanding. The rate of expansion however varies with different observations. The age of the Universe was calculated by measuring the faintest light observed from the oldest stars of the universe and also by the Red shift data. The data provides expansion details which if winded back will take us to the point of singularity i.e the start of the big bang., thus calculating the age of the Universe in the process.