# GCSE Physics P7 (OCR) - Astronomy

Flashcards by Josh Price, updated more than 1 year ago
 Created by Josh Price almost 5 years ago
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### Description

GCSE Physics (P7) Flashcards on GCSE Physics P7 (OCR) - Astronomy, created by Josh Price on 04/22/2015.

## Resource summary

 Question Answer Which direction does the Sun, the stars, and the moon appear to travel in? East-West How long does it appear to take the sun, the stars, and the moon to travel across the sky? 24 hours. Slightly less than 24 hours. Slightly more than 24 hours. What is a sidereal day? A rotation of 360d of the Earth. What is a solar day? The average time it takes the sun to cross the sky. Why is a sidereal day different to a solar day? Because with a solar day, the Earth moves a short distance around its orbit, so it has to turn further (4 minutes) for the sun to appear in the same place as the day before. Which planets can be seen with the naked eye? Mercury, Venus, Mars, Jupiter, and Saturn. How do planets appear to move? They move with the stars, but also change their position relative to the fixed stars? Why do the planets appear to move in retrograde motion? Because both the Earth and the planets are orbiting the sun. Each planet takes a different amount of time to orbit the sun. It depends where the planet is in its orbit, as to whether the planet is being 'overtaken' or 'going backwards' or 'catching up'. Why do solar eclipses occur? Solar eclipse = The moon blocks the Sun's light. The sun moves slightly faster than the moon, and its path may take it directly behind the moon. Why do lunar eclipses occur? Lunar eclipse = The moon moves into the Earth's shadow. The moon's path may take it directly behind the Earth, at the point where all sunlight from the Sun is blocked. Why are eclipses rare? Because the moon's orbit is tilted relative to the plane of the Earth's orbit by about 5d. This means that usually the Sun, moon, and Earth are not in line, so no eclipse occurs. Why are different stars seen in the night sky at different times of the year? Because the Earth travels halfway around its orbit in six months. You see the stars that are in the opposite direction to the Sun, so after six months you will see the opposite half of the sky. What is the angle of 'right ascension'? The angle to the star East from the vernal equinox to the star. It's measured in hours, minutes, and seconds. What is the angle of 'declination'? The angle of the star above or below the celestial equator. Its measured in degrees and minutes.

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