The Earth-Moon-Sun System Flashcards
(10 cards)
What is precession and what are the effects
Precession is the wobbling of the Earths axis over a 26,000 year cycle caused by the Sun and Moon’ gravity.
It can change the apparent locations of stars and cause ancient monuments to be misaligned
What are the different types of solar eclipses
Total solar eclipses involve the Moon completely blocking out the Sun for a few minutes.
Partial solar eclipses involve the Moon partially blocking the Sun
Annular solar eclipses involve the moon appearing slightly smaller, and the Sun becoming visible around the outside
What are the different types of lunar eclipses?
Total Lunar eclipse, the whole moon passes into the Earths shadow and appears a deep red due to light refracted by our atmosphere.
Partial Lunar Eclipse, the moon appears partially darkened, and the rest is still visible.
What is meant by the term umbral contacts
When the Eclipsed body is leaving or entering the umbra. There are 4, which occur at the each of the two points of contact with the sides of the body.
How was Earths diameter determined
By Erastothenes observing that no shadows were cast on the Tropic of Cancer (Syene) on the Summer Solstice, but they were in a more northerly city (Alexandria)
Circumference of Earth/ Distance from Syene to Alexandria = 360/difference in angle of shadows
How was the moons diameter determined
Aristarchus observed a total solar eclipse and used the formula
Diameter of Moon/Diameter of Earth=TimeU1 to U2/Time U2 to U4
How was the distance to the moon calculated?
Aristarchus then determined the distance to the moon by holding his thumb at arms length and seeing that it only just obscured the moon. Knowing the size of the moon, and the relative sizes of his thumb and arm, he could work about the distance,
How was the diameter of and distance to the sun calculated?
Aristarchus waited until the moon was at first quarter, and calculated the moon-sun angle. He then used trigonometry to estimate the Sun as being 20x further away than the moon(real value 400). As they appear the same size, he reasoned that the Sun must also be 20x bigger
How does the moon cause high and low tides
The moons gravity causes a bulge on the side nearest the Earth, meaning high tide. The opposite side also gets a high tide due to inertia, so the low tides occurs at right angles
Explain spring and neap tides in relation to the sun
When the Earth, Sun and Moon are in a straight line, there is more force acting, so there is the greatest tidal range:high tides are higher and low tides are lower, these are called spring tides
When the Moon and Sun are at right angles to the Earth (at first and third quarter), the Sun’s gravity partially cancels out the Moon’s pull. This means there is less force acting in a straight line, so there is the lowest tidal range: high tides are lower and low tides are high, these are called neap tides
