# P7 Physic

Physics p7

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## Parallax

The Earth moves around its orbit, as it moves around it's orbit the stars appear to move.

This affect is called parallax.

The closer the star, the greater the affect.

We can use the parallax angle to measure the distance to stars.

If the parallax angle is one second of an arc, we say it is one parsec.

1 parcec is approximately 3.26 light years.

Thwe..
The closer the star to us, the greater the effect is

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## Intrinsic brightness

The intrinsic brightness depends on the temperature and size.

The observed brightness depends on the intrinsic brightness and the stars distance from Earth.

Cepheid variable stars pulsate in brightness. The period of pulsation is related to their brightness.

It is thought that changes are caused by regular expansions and contractions of the star.

You can use the cepheid variable to measure the distance to nearby galaxies.

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## Galaxies

The Milky Way is our galaxy.

Fuzzy blobs are nebulae, stars are distinct points.

Harlow Shapely thought that nebulae weren't that far away.

Heber Curtis claimed that they were megaparsecs away, in fact the Milky Way is our galaxy and the other fuzzy nebulae are other galaxies.

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## Naked Eye

The Sun rises in the East and sets in the West, it's highest point is at midday.
The Earth spinning on it's axis causes day and night. The Sun is stationary.

The Earth spins on it's axis as well as orbitting the sun. It takes 365days to do this, one year.

The Earths axis is tilted, and therefore the Sun's energy is highly distributed to some parts more than others. This inclinates the seasons.

All 8 planets have elliptical orbits around the Sun. Which means they're slightly squished circles.

At night the stars appear to move across the sky in curved paths. This is due to the Earth spinning on it's axis.

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## Planets

Planets seem to move across the night sky. The 'wandering stars', this is because the planets are much closer to the Earth than the stars, so as they orbit the sun at a different speed to the Earth, they appear to wander across the background of fixed stars.

Some planets appear to move in reverse, which is called retograde motion. This is because they're further away from the sun than we are, so there orbit is slower.

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## Eclipses

A Lunar eclipse occurs when the moon passes into the Earth's shadow.
A Solar eclipse occurs when the moon passes inbetween the Sun and the Earth.

The moon takes 28 days to orbit the Earth but eclipses do not happen regularly as theorbit of the moon is tilted relative to the plane of the ecliptic.

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