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Flashcards in Earth, Sun and Moon Deck (18):
1

What is the Sun? Is it a perfect sphere? Explain the diameters.

The Sun (or Sol), is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10km in diameter between the poles and the equator.

2

What is the average radius of the sun? Compare this figure to Earth. How much of this is the core? What is the temperature of the center of the sun?

The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core.

At its centre the Sun reaches temperatures of 15 million °C.

3

What colour is the sun? What is it composed of? What is the sun (main sequence)? How old is the sun? How much bigger is the sun than Earth?

The Sun is all the colours mixed together, this appears white to our eyes.
3.The Sun is mostly composed of hydrogen (70%) and Helium (28%).
4.The Sun is a main-sequence G2V star (or Yellow Dwarf).
5.The Sun is 4.6 billion years old.
6.The Sun is 109 times wider than the Earth and 330,000 times as massive.

4

What is the dominant object in our solar system? How heavy is it? What does it provide? What does everything in the solar system orbit around? What orbits directly and what orbits indirectly?

The Sun is the centre of our solar system, and by far the dominant object in it. As well as providing the light and heat which power all life on Earth, it is by far the most massive object in the solar system: more than 300,000 times heavier than the Earth, and over 700 times heavier than all the planets put together. This huge mass acts as the anchor for the whole system: all of the other objects in the solar system — planets, asteroids, moons, etc. — are in orbit around the Sun, either directly, or indirectly as moons of other objects.

5

What are the other objects in the solar system. Where is Earth situated from the sun? Talk about our moon? How often does the moon circle the Earth? How close is the Moon compared to the Sun?

The main other objects in the solar system are the eight planets, each of which circles the Sun in its own orbit. Our own Earth is the third planet out from the Sun. Most of the planets have moons in orbit about them, and Earth is no exception; our Moon orbits around us once per month, and so gets carried along with us in our journey around the Sun.
Our Moon is fairly unremarkable, except for its size; it is one of the larger moons in the solar system. The main reason it looks so big to us, though, is simply that it is very close; the Moon is just 384 thousand km away. By comparison, the Sun is 150 million km away.

6

Explain how we have nights and days?

At any given time, half the Earth is illuminated by the Sun and that is the half of the Earth on which people can see the Sun and this is the day side. The other half of the Earth receives no direct light from the Sun, and hence is in darkness; looking at it from our point of view. The Sun isn't visible because it's round behind the other side of the Earth. This is the night side.

7

Does the sun move? Do other planets play a role in our eclipses? Is their only one object orbiting Earth? What is the only natural object orbiting Earth? What causes eclipses?

No the other planets don't play a role in eclipses. For our purposes, we're interested in the Sun, the Earth, and the Moon, and how they relate to each other.

The Sun is the centre of the solar system, so when discussing the structure of the solar system, it's appropriate to think of the Sun as sitting still (though it does actually move within our galaxy).
Orbiting the Sun is Earth, with its moon.

The Moon is the only natural object orbiting the Earth (there are thousands of man-made satellites).

This is how our Earth and Moon relate to each other and to the Sun and it is the motions that cause eclipses.

8

Does the sun move? How long does it take for the am Earth to rotate?

The Earth is rotating so over the course of 24 hours — which is how long it takes the Earth to do one complete rotation — every part of the Earth sees a day and a night. It is the rotation of the Earth that makes the Sun appear to move across the sky, when it is actually sitting still.

9

What would a person standing in the same place on Earth for 24 hours see? Explain Sunrise,Noon,Sunset,Midnight.

Somebody standing on the Earth would be on the side facing the Sun at noon. The rotation of the Earth would carry them anti-clockwise towards the point of sunset; from their point of view, the Sun would appear to be going the other way, and to be getting lower in the sky. When our observer reached the sunset point, the Sun would be exactly on the western horizon from their point of view; then they would move around to the night side. At midnight they would be on the side of the Earth opposite the Sun; then they would move on towards the point marked sunrise, where they would see the Sun appear on the opposite (eastern) horizon. As the Earth continues rotating, they would see the Sun climb in the sky until they were once again directly in line with it at noon.

10

What is the brightest object in the night sky? Does it glow? How does it reflect light? Why is the moon very bright?

The Moon is by far the brightest object in the night sky, far outshining all the stars and other planets. So what makes it glow? Well, in fact, it doesn't "glow" at all — like all the other planets, the Moon is only visible because it reflects light from our Sun, the only large-scale source of light in our solar system. (The stars, of course, are Suns in their own right, and in their own solar systems). The Moon is very bright simply because it is pretty big, and very close to us compared to the other planets, and so it reflects a lot of sunlight our way.

11

What happens every month to the moon? What is a common false theory about the moon cycle? Why is this wrong?

Every month, though, something happens the Moon shrinks, first to a half moon, then a crescent, then vanishes entirely at the New Moon. Then, it starts growing again from crescent, to half, and then to Full Moon. These are called the phases of the Moon. It's a not uncommon misconception that the Moon goes through these phases because of the shadow of the Earth. This isn't true, though — if you look at the diagram on the next slide, you will see that the Moon couldn't be in the Earth's shadow for more than a small portion of its orbit at most. In reality, if we were to look at a properly scaled diagram, we would see that the Earth is even smaller in proportion to the Moon's orbit, and so the Moon wouldn't be in the Earth's shadow for more than a few hours a month. Since the phases of the Moon last for a whole month, something else must be causing them.

12

What does cause the moon cycle?

The answer is that the Moon is only half-lit; and we're seeing different angles of the half-lit Moon as it orbits around the Earth. Just like the Earth, only the side of the Moon facing the Sun is lit by it; the rest is in darkness. When we look at the Moon, depending on the angle it is at, we may see the lit side, or the unlit side, or part of the lit side and part of the unlit side; and this is what causes phases. The Moon goes through a complete cycle of phases from New to Full and back to New in one orbit around the Earth; this is a lunar month, which is 29.5 days on average.

13

Explain solar and lunar eclipses?

All solar eclipses involve the Moon passing between the Earth and the Sun, and casting a shadow on the Earth. However, the type of eclipse which can be seen from a given location depends on whether the Moon passes directly, or only partly, between the Earth and Sun; but also on where on Earth you stand to observe it, and on a number of other factors.

14

When does a solar eclipse happen? How often does a total eclipse happen? How often does a partial eclipse happen? Where do you have to be to see a solar eclipse? What are the chances of seeing one? (In years.)

A solar eclipse happens when the moon gets in the way of the sun’s light and casts its shadow on Earth. That means during the day, the moon moves over the sun and it gets dark. This total eclipse happens about every year and a half somewhere on Earth. A partial eclipse, when the moon doesn’t completely cover the sun, happens at least twice a year somewhere on Earth.
But not everyone experiences every solar eclipse. Getting a chance to see a total solar eclipse is rare. The moon’s shadow on Earth isn’t very big, so only a small portion of places on Earth will see it. You have to be on the sunny side of the planet when it happens. You also have to be in the path of the moon’s shadow.
On average, the same spot on Earth only gets to see a solar eclipse for a few minutes about every 375 years!

15

How does a lunar eclipse occur? Why can the moon be red? Why are sunsets and sunrises red and orange? What happens during a total lunar eclipse? What is a good way to remember the two eclipses?

During a lunar eclipse, Earth gets in the way of the sun’s light hitting the moon. That means that during the night, a full moon fades away as Earth’s shadow covers it up.
The moon can also look reddish because Earth’s atmosphere absorbs the other colors while it bends some sunlight toward the moon. Sunlight bending through the atmosphere and absorbing other colors is also why sunsets are orange and red.
During a total lunar eclipse, the moon is shining from all the sunrises and sunsets occurring on Earth!
It’s easy to get these two types of eclipses mixed up. An easy way to remember the difference is in the name. The name tells you what gets darker when the eclipse happens. In a solar eclipse, the sun gets darker. In a lunar eclipse, the moon gets darker.

16

Why don’t we have a lunar eclipse each month? Why?

You might be wondering why we don’t have a lunar eclipse every month as the moon orbits Earth. It’s true that the moon goes around Earth every month, but it doesn’t always get in Earth’s shadow. The moon’s path around Earth is tilted compared to Earth’s orbit around the sun. The moon can be behind Earth but still get hit by light from the sun.

17

What do many people believe? Is Earth closer to the sun at certain parts of the year? What does this cause? Why does Earth have seasons?

Many people believe that Earth is closer to the sun in the summer and that is why it is hotter. And, likewise, they think Earth is farthest from the sun in the winter. This is incorrect.

It is true that Earth’s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is closer to the sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the sun and summer when it is farthest away! Compared with how far away the sun is, this change in Earth's distance throughout the year does not make much difference to our weather.
There is a different reason for Earth's seasons.Earth's axis is an imaginary pole going right through the center of Earth from "top" to "bottom." Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth's surface gets some of each.
Earth has seasons because its axis doesn't stand up straight.

18

Explain why Earth has seasons?

The NH is in spring when
The SH is in autumn.
The NH is in summer when
The SH is in winter.
The NH is in autumn when
The SH is in spring.
The NH is in winter when
The SH is in summer.