Topic 1.4 - Earth-Sun-Moon Interactions

Question 1

Why is the moon visible

Answer 1

It reflects sunlight

Question 2

Explain how eclipses are possible.

Answer 2

Although the sun is about 400 times farther from Earth than the moon is, it is also about 400 times larger in diameter. This means that angular sizes of the sun and the moon are almost exactly the same when observed from the Earth and the sun and moon appear to be the same size in the sky

Question 3

Explain a total solar eclipse.

Answer 3

When the moon passes directly in front of the sun, it can obscure light from the Sun’s photosphere and produce a spectacular total solar eclipse for observers in the umbra on Earth

Question 4

What is Baily’s Beads?

Answer 4

Small bright spots of sunlight caused by the Sun’s rays shining through valleys on the moon

Question 5

When do solar eclipses occur (moon phase)?

Answer 5

New moon

Question 6

How long do solar eclipses last?

Answer 6

Usually a few minutes

Question 7

Why doesn’t a solar eclipse occur every full moon?

Answer 7

The plane of the moon’s orbit around the Earth is tilted by about 5º to the plane of the Earth’s orbit around the sun. This means that at most new moons the moon is either above or below the sun in the sky

Question 8

Explain a partial solar eclipse.

Answer 8

If the moon only partly obscures light from the sun (i.e. part of the Earth’s surface lies in the penumbra) then an observer views a partial solar eclipse. The sun appears to have a circular ‘bite’ missing from its disc due to the silhouetted moon

Question 9

What happens in a lunar eclipse?

Answer 9

The Earth casts the shadow and prevents sunlight from reaching the moon. During totality, the moon is not invisible but appears from Earth as a red/copper-coloured full moon.

Question 10

What phase is the moon in during a lunar eclipse?

Answer 10

Full moon

Question 11

How long does totality last?

Answer 11

About 30 mins to an hour

Question 12

Why is the moon copper coloured in a lunar eclipse?

Answer 12

Light from the sun passes through the atmosphere around the ‘edge’ of the Earth and most blue light is scattered to leave mainly red light. The red light is refracted by the Earths atmosphere and illuminates the moon

Question 13

What is an umbra (in an eclipse)?

Answer 13

If an observer was in the umbra during an eclipse, the observer would see a total solar eclipse

Question 14

What is a penumbra (in an eclipse)?

Answer 14

If an observer was in the penumbra during an eclipse, the observer would see a partial solar eclipse

Question 15

Explain a partial lunar eclipse.

Answer 15

When the Earth prevents only some of the light from falling onto the Moon, the curved shadow of the Earth can be seen on the (otherwise) full moon, causing a partial solar eclipse

Question 16

What is a sidereal day?

Answer 16

The time taken for successive crossings of a given star across an observer’s meridian

Question 17

How long is a sidereal day?

Answer 17

23 hours and 56 mins

Question 18

What is a solar day?

Answer 18

The time taken for successive crossings of the sun (any give part of it) across the observers meridian

Question 19

How long is a solar day?

Answer 19

Exactly 24 hours

Question 20

Why is there a 4 minute difference between the solar day and sidereal day?

Answer 20

The extra 4 minutes are needed because during one complete Earth-rotation, our planet has moved slightly in its orbit around the sun and it must rotate for an extra 4 minutes to allow the sun to return to the same position in the sun

Question 21

Why do we not move across the sky in a uniform manner every day?

Answer 21

The Earth orbits the sun in an elliptical orbit (not circular) and the Earths polar axis is tilted to the plane of the orbit, causing the sun to be ‘higher’ in the sky in summer compared to winter

Question 22

What is the Equation of time?

Answer 22

EOT = apparent solar time - mean solar time (GMT)

Question 23

Describe the appearance of the Aurora Borealis/Aurora Australis (more commonly known as the Northern/Southern lights.

Answer 23

Dynamic, dazzling displays of green, yellow and red curtains and whirlpools of light in the sky.

Question 24

What are the Aurora Borealis caused by?

Answer 24

Electrons from the solar wind that have been accelerated to high speeds in the Earth’s magnetic field, exciting atoms and molecules of oxygen and nitrogen in the upper atmosphere (at heights between 100-1000 km. As the atoms or molecules de-excite, they emit light at certain wavelengths that are characteristic of the element concerned

Question 25

Where does fast solar wind originate from?

Answer 25

Coronal holes (cooler regions of the corona close to the sun’s magnetic poles