Chapter 12

Here is a Chapter 12 – Solar System. If you spot anything ‘hinky’ then just let me know! 😛

1. a) Why do the bright planets seem to keep to the zodiac, instead of wandering about all over the sky?
Our solar system are all on one plain. The planets orbit the Sun on the same level as each other, creating a plate like shape.

1. b) Why do the giant planets contain more hydrogen and helium than the Earth does?
Whilst the Sun was being created, the planets began to form around it, in the ‘solar nebula’. The planets closer in to the Sun, once formed managed to lose the lighter atoms, such as hydrogen and helium; while the larger planets further out managed to keep hold of all it’s atoms.

1. c) What do we believe to be the approximate age of the Earth and the other planets?
We believe that the approximate age of the Earth and other planets to be around 4.6 billion years old.

2. a) Explain, with a diagram, why the Moon shows phases.
The phase of the Moon depends on where it is positioned whilst orbiting the Earth. When the Moon orbits the Earth, the amount of light from the sun that is reflected back to Earth creates the phases.The Moon's Phases
So, if the Moon is in between the Earth and the Sun, then we see no light. This is because the lights up the back of the Moon and not the front.
But around day 7, it has just done a quarter of it’s orbit and it lights up half of the Moon on the side we see, and half of the side we don’t see. This results in a half Moon.
This continues during the whole orbit of the Moon around the Earth.

2. b) What is the phase of the Moon at the First Quarter?
The phase on the Moon at the First Quarter is a half moon.

2. c) The Moon takes 27.3 days to complete one orbit, but the interval between successive new moons is over 29 days. Why?
The Moon has a set time on it’s orbit, because the orbit is completely based on where the Moon is positioned. The reason why the difference between new moons are more than 2 days, is because the Moon’s phases rely on the Sun as it orbits the Earth. But the Earth is orbiting the Sun at the same time as the Moon orbits the Earth, increasing the time of one Lunar phase cycle.

3. a) Why does Mercury show obvious phases, whereas Jupiter doesn’t?
Mercury shows obvious phases, because it relies on the Sun to light up the surface. Jupiter is not lit up by the Sun, as the light that reaches Jupiter is very little. Jupiter uses its own independent heat source to be lit up by, so it can’t have phases when it lights itself up.

3. b) Are there any occasions when we can see Mercury when it is at inferior conjunction? If so, when?
Yes, but we can only see Mercury at inferior conjunction when the lining up is exact with the Sun. Then we see Mercury during transit, as it crosses across the Sun. The next Mercury transit will be on May 10, 2016.

3. c) Name the two inferior planets.
The two inferior planets are Mercury and Venus.

4. a) Draw a diagram to show the orbits of the Earth and Mars. Indicate the positions of the two planets when Mars is at opposition. Earth and Mars Opposition

4. b) Why are not all oppositions of Mars equally favourable?
Mars has a less circular orbit than Earth, so it cannot have equally favourable oppositions.

4. c) Why are there times when Mars seems to have apparent retrograde motion against the stars?
Because the Earth has a faster average velocity than Mars, Earth can pass Mars once, and them manage to pass it again on the inside, making Mars look like it is going backwards, or going in apparent retrograde motion.

5. a) Explain why the synodic period of Saturn is shorter than that of Mars.
The synodic period of Saturn is shorter than Mars because Saturn has such a large orbit, by the time the Earth has done one orbit of the Sun, then Saturn hasn’t had much time to move further, and is caught up quite quickly. Mars is closer and has a similar velocity, meaning it takes longer for the Earth and Mars to meet up again.

5. b) Why does Saturn appear less brilliant than Jupiter in the sky? SaturnGive two reasons.
One reason why Saturn appears less brilliant than Jupiter is because it is smaller. If it is smaller, then it gives out less heat energy for it to be seen by.
Another reason is because it is further away, meaning the light from Saturn has to travel further than Jupiter.

5. c) Halley’s Comet has an eccentric orbit, and has retrograde motion. Draw a diagram to illustrate this, pulling in the orbits of the Earth and Neptune.Halley's Comet, Neptune and the Earth: Their Orbits

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