Page 9 - Curriculum Visions Dynamic Book

A hydrogen atom weighs 1.0078 atomic mass units, but a helium atom weighs 4.0026. So, as four hydrogen atoms lose their electrons and then fuse into a helium atom, there is some mass left over.
Einstein showed that mass and energy are related by the formula:
e=mc2
where e = energy, m = mass, c = the speed of light
In the Sun’s nuclear reactions about five million tonnes of matter are converted into energy every second.
Put another way, every second about 700,000,000 tonnes of hydrogen are converted to about 695,000,000 tonnes of helium, leaving 5,000,000 tonnes of energy in the form of radiation. The Sun’s resulting energy output is 386 billion billion megawatts.
This energy is emitted in various forms of light (ultraviolet light, X-rays, visible light, infrared light) and microwaves and radio waves. The Sun also emits energized particles (neutrinos, protons) that make up the solar wind (see page 38). These various forms of energy strike Earth, where they warm the planet, drive our weather, and provide energy for life. We are not harmed by most of the radiation or solar wind because the Earth’s atmosphere protects us.
The life of a star
A star like the Sun can continue to shine as a result of fusion reactions for as long as there is hydrogen left
as a fuel. Gravity keeps pulling the hydrogen together, but the fusion reaction creates searingly hot gas, which tries to expand. The balance of forces keeps the star
a stable size with little variation in its brightness for much of its life. During all of this time the star looks similar to the majority of others in a galaxy and is said to belong to the main sequence. If it is of modest size, like the Sun, most of its life is spent this way.
Such stars, including the Sun, have enormously long lives. Much bigger stars are brighter but burn up faster and have shorter lives.
atmosphere The envelope of gases that surrounds the Earth and other bodies in the universe.
atom The smallest particle of an element. atomic mass unit A measure of the mass of
an atom or molecule.
core The central region of a body.
fusion The joining of atomic nuclei to form heavier nuclei.
gravity The force of attraction between bodies. infrared Radiation with a wavelength that is
longer than red light.
main sequence The 90% of stars in the universe that represent the mature phase of stars with small or medium mass.
matter Anything that exists in physical form. molecule A group of two or more atoms held
together by chemical bonds.
neutrinos An uncharged fundamental particle that is thought to have no mass.
nucleus (pl. nuclei) The centermost part of something, the core.
pressure The force per unit area.
radiation The transfer of energy in the form of waves (such as light and heat) or particles (such as from radioactive decay of a material).
radio telescope A telescope that is designed to detect radio waves rather than light waves.
radio waves A form of electromagnetic radiation, like light and heat. Radio waves have a longer wavelength than light waves.
ultraviolet A form of radiation that is just beyond the violet end of the visible spectrum and so is called “ultra” (more than) violet. At the other end of the visible spectrum is “infra” (less than) red.
x-ray An invisible form of radiation that has extremely short wavelengths just beyond the ultraviolet.
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