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All stars get their energy from this process. The combining of the nuclei of lighter elements to from heavier elements.

fusion of hydrogen into helium

When 4 hydrogen nuclei(or protons) come together, they produce a helium nucleus of two protons and two neurons. Energy is released in this reaction.


A place of intense heat and pressure - so intense that atoms are torn apart into their component nuclei and electrons. As a result elements such as hydrogen and heleim exist as plasma.

A plasma

The fourth state of matter consisting of charged particles-the nuclei, or ions which have a positive electric charge, and electrons which have a negative charge.

Layer of the sun

Core - Radiative Zone (another layer of plasma) - Confection Zone - photoshere(visible surface) - Chromosphere(inner layer of suns atmosphere) - Corona


Dark spots on the photoshere


Displays of colors and light appearing in the upper atmsphere, common in the regions near Earth's magnetic poles.

Cause of auroras

As solar wind blows past Earth, some particles interact with Earth's magnetic field and upper atmosphere.

Ptolemy's Geocentric Model

Imagined planets on a small circular orbits called epicycles. The center of each small orbit moved around Earth on a larger circular orbit called a deferent.

retrograde motion

planets sometimes appear to go backward during orbit. the effect is due to Earth catching up with and passing the planet

Copernicus's heliocentric model

Sun centered model. Earth and the other planets rotated around the sun.

Tycho Brahe

Studied the movement of the moon and planets throughout their orbits..

Johannes Kepler

unexpected occurance could be explaned if orbits were ellipitical not round.

Kepler's first law

States planets travel in ellipitical orbits with the sun at one focus(ellispe has two foci) on opposite sides of its center. Because the sun is at one focus on the ellispe, a planets orbit will change throughout its orbit.

Kepler's second law - - equal area law

states that each planet moves around the sun in such a way that an imaginary line joining the planet sweeps over equal areas of space in equal periods of time

Kepler's third law- harmonic law

The time it takes a planet to travel one orbit around the sun is its periods.

Sir Issac Newton

Developed explanation o what keeps the planets in motion. Defined and articulated three laws of motion and the law of gravitation.

Newton's first law

An obbject will move forever in a straight line at the same speed unless a unless some external force changes its direction or speed.

Law of Gravity

Every mass exerts a force of attraction on every other mass, and the stregnth of that force is proportional to the masses and inversely proportional to the distance between them.

Kepler and Newton

Kepler had realized that the planets did not move with constant speeds. With the law of gravitation,, Newton was able to explain why they do not. Newton's laws still explain almost all the largescale interactions we see in the universe.

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