Topic 1 - Earth, Moon and Sun

8/13/2019 Topic 1 - Earth, Moon and Sun

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Topic 1 - Earth, Moon and Sun

Planet Earth The Moon The Sun Earth Moon Sun Interactions

Earth Facts

Why is Earth Special?

Latitude and Longitude

The Atmosphere

Light Pollution

Two kinds of Telescope

Moon facts

Moon Features

Exploring the Moon

The Origin of theMoon

Sun Facts

Sunspots

Fusion

Observing theSun

Solar Wind

Phases of the Moon

The Moon in Orbit

Solar Eclipses

Lunar Eclipses

How Long is a Day?

Shadow Sticks and Sundials

The Equation of Time

Aurorae


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Auroraedescribe aurorae and recall from where on Earth they are most likely to be observedexplain how aurorae are caused.

The aurora borealis are otherwise known as the northern lights. It is now understood that they are caused bycharged particles from the solar wind striking the atmosphere and making the molecules they hit emit light.The aurora australis occurs close to the south pole.

The Sun emits a huge amount of charged particles all the time, this is the solar wind. These particles takeabout 2 days to reach Earth. When they do they are deflected by the Earth's magnetic field and manyparticles enter the atmosphere at the poles. Aurorae are usually just observed at extreme northern orsouthern latitudes, e.g. in countries like Alaska and Antartica.

pic N ASA


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The Equation of Timedemonstrate an understanding of the terms apparent Sun and mean Sundemonstrate an understanding of the term equation of time (apparent solar time mean solar time) and perform simple calculations

Gordon lives in Greenwich. He makes a shadow stick to record at what time the Sun is at its highest point. He finds that onsome days it is at its highest before 12:00 and on some days after 12:00. He records the difference every day and plots agraph of how far ahead the sundial is.

The difference between the sundial time and standard time (clock time) is called the Equation of Time .

For someone living at Greenwich or after accounting for longitude

Equation of time = Apparent Solar Time - Mean Solar TimeThe reason for the difference is due to the orbit of the Sun is not being circular and because the Earth's axis ofrotation is tilted .

All days throughout the year are not exactly 24 hours long. They can be up to 30s longer or shorter. Over a month or so thedifference can add up to as much as 16 minutes. Over the course of a year however (actually 4 years) both times end upwhere they started from.

The equation of time can be positive or negative as you can see on the graph above.

When solar time is ahead of standard time it is positive.

When solar time is behind standard time it is negative.

Greenwich Mean Time is a system which assumes that every day is exactly 24 hours long. This is obviously forconvenience. Before railways (and the need for accurate timetables) it didn't matter very much if the time in Manchester orNewcastle was slightly different to what it is in London or if noon varied slightly from day to day. Now it does very much.

The length of a day (i.e. from noon till noon) can vary quite a bit. Greenwich Mean Time is a system based on an imaginarysun that takes exactly 24 hours from noon till noon every day. It is called a mean sun .

Are you confused?

This is a tricky topic which takes a while to get your head around. It is worth the effort as there is nearly always a bigquestion on this in the exam.

Study the data in this table. The last few are for you to complete.


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I find it useful to remember the equation of time on a particular day is how far ahead your sundial is compared to your clock.

Equation of Time(mins)

GMT(the same in all 3

locations)

Apparent Time inGreenwich(0 degrees)

Apparent Time inTruro

(4 degrees West)

Apparent Time inLowestoft

(2 degrees East)

0 12:00 12:00 11:44 12:08

0 12:34 12:34 12:18 12:42

+7 12:00 12:07 11:51 12:15

+13 11:50 12:03 11:57 12:11

-3 09:00 08:57 08:41 09:05

-9 14:45 14:36 14:20 14:44

0 16:00

+4 13:00

-6 10:00


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How Long is a Day?describe the terms solar day and sidereal dayexplain why a solar day is longer than a sidereal dayinterpret charts and diagrams showing the variation in daylight length during a year demonstrate an understanding that there are seasonal variations in the rising and setting of the Sun

pic Ian Britton - Freefoto.com

The Sun rises in the East and sets in the West. It culminates (reaches its highest point) around noon.

How much time passes between sunrise and sunset? Obviously this varies throughout the year. In winter thesun rises later in the day and sets earlier. We should understand these patterns. Below is a download link to aspreadsheet of sunrise and sunset times. You are going to analyse this data looking for patterns. We will thenexplain these patterns in terms of the relative motion of the Sun and Earth.

Right click HERE and choose "save target as" to download an Excel file of sunrise and sunset times inLondon in 2005.

Use this data to produce the following graphs.

1. How sunrise time varied throughout the year.


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2. How sunset time varied thought the year.

3. How the number of daylight hours varied throughout the year.

From these graphs and/or the data find

a) Which was the longest day? b) Which was the shortest? c) Which two days had 12 hours of daylight?

What is daylight saving? Why was it introduced?

The cycles of life on Earth are bound to the seasons. In the summer it is warm, the Sun is high in the sky andthe days are long. In winter it is cold, the Sun is low in the sky and the days are short.

Days vary in length throughout the year due to the tilt of the Earth.

The Earth receives many types of electromagnetic radiation from the Sun. The important two are light andheat (infra red). For six months of the year the Northern hemisphere is titled towards the Sun. Radiation fromthe Sun arrives from almost above our heads. For the other six months the northern hemisphere is tilted awayfrom the Sun. Radiation from the Sun arrives at angle.

Because of thisa) it is much more spread out over a larger area so it is less concentrated and

b) it passes through a much thicker amount of atmosphere so more of it is absorbed before it reaches theEarth.

Ian Britton - Freefoto.com

Spring Summer

Autumn Winter


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Shine a torch on a piece of paper. Now turn the paper through 45 degrees so that the light hits it an angle.How does this explain why it is colder in the winter?


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Lunar Eclipsesdescribe the appearance of partial and total lunar eclipsesdescribe, using diagrams, the mechanisms causing lunar eclipses

A lunar eclipse occurs when the shadow of the Earth falls on the Moon. They can only occur when there is a full Moonand, like total solar eclipses, are quite rare. Not as rare though as the Earth's shadow is much bigger than the Moon's.

pic NASA

Penumbral Eclipse - The Earth blocks out some light from the Sun. Not really noticeable from Earth withoutspecial equipment.

Partial Lunar Eclipse - Part of the Moon is completely blocked of sunlight, i.e. is within the umbra shadow.

Total Lunar Eclipse - All of the Moon falls within the umbra.

The Appearance of the Moon

Sunlight which passes through the Earth's atmosphere is scattered, as in a sunrise or sunset. Blue light is scattered inall directions so the light which goes to fall on the Moon is from the red end of the spectrum and the Moon appears abeautiful pale red colour.

Totality, when the Moon is completely in shadow, lasts much longer than for a solar eclipse as the shadow of theEarth is much bigger than that of the Moon. Up to over 100 minutes.


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The Moon in Orbituse diagrams to explain why the lunar phase cycle is (2.2 days) longer than the orbit period of the Moon

The Moon orbits the Earth every 27.3 days. Like the Earth the Moon is also spinning but with a period of 27.3days. The result of this is that the same side of the Moon is always facing the Earth. Until man made probeswere sent to orbit the Moon we had never seen the far side.

How long does a cycle last?

Although it takes 27.3 days for the Moon to orbit the Earth the lunar cycle above actually takes 29.5 days,more than two days longer.

This is because as the Moon orbits the Earth the Earth moves relative to the Sun, so an extra couple of daysare needed for the Moon to get into the position it was in, relative to the Earth, when the cycle started.


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Phases of the Moonrecall the period of the lunar phase cycle (29.5 days)demonstrate an understanding of lunar phases and deduce the lunar phase cycle from given data

Of course the Moon does not appear the same in the sky throughout the course of a lunar month. As the Moonrotates around the Earth different parts of the Moon are in sunlight and others are in darkness. At any time we maysee all, some or none of the half of the Moon which is in sunlight.

You must be able to recognise and name the phases shown below.

pic - NASA

Remember - Waxing = getting bigger Waning = getting smaller


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Shadow Sticks and Sundialsinterpret simple shadow stick data to determine local noon and observers longitudedescribe how a sundial can be used to determine time

A Simple Sundial

Put a stick upright in the ground. Congratulations, you have made a very crude sundial. The shadow cast by the stick will move throughout the course of the dayust as the hour hand of a clock moves. Every hour make a mark where the shadow is and you have a sun clock. This will give you a rough idea of what time ofday it is but probably not a very accurate one. Why not?

Longitude Correction

Because the sun rises in the east and sets in the west people who live east of Greenwich get the sun earlier and people west of Greenwich get it later. In fact forevery degree east you are your local noon will be 4 minutes sooner and for every day west it will be 4 minutes later. (If you divide the number of minutes in a dayby 360 you get ...?) You should see then that by measuring the difference you can calculate your longitude. E.g. local noon in Truro happens 20 minutes after itdoes in Greenwich. This is because its longitude is 5 degrees West.

Remember - for every degree East of Greenwich you are your local noon happens 4 minutes sooner.

Why aren't my hour markers evenly spaced?

The position of the shadow not only depends on your longitude but also on your latitude as you should see from the diagrams below.

What you can find with a shadow stick is the the time at which you local noon occurs on aparticular day. This is the time when the sun is at its highest in the sky, i.e. it culminates. When thishappens the shadow made by the stick will be at its shortest.

There are two reasons why there will be a difference between GMT, what your clock says, andyour local noon.

1. We must take into account the Equation of Time . This will be explained in depth on the next page .

2. Your longitude will affect what the sundial reads and so needs to be corrected for.


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If you want your hour markers to be evenly spaced then the stick which makes the shadow, the gnomon, needs to be parallel to the Earth's axis. The solution is tomount the stick at an angle. It should lean to the north at an angle equal to the latitude of the location where the sundial is. The gnomon should then be parallel tothe Earth's axis.

The sundial above is called an equatorial sundial where the plate on which the shadow falls is at right angles to the gnomon and therefore is on a plane parallel to

the equator.. There are several other types.

The lines on the base of a horizontal sundial, e.g. the one above, are worked out using a complicated mathematical formula. There are plenty of places on theinternet where you can download a template.

Have a look at www.sundials.co.uk for lots of different designs.

Images with kind permission from www.sundials.co.uk

Bear in mind that your sundial is telling you your local solar time . Unless you live on the same longitude as Greenwich this will be slightly different to what yourwatch says. If you were to set up a sundial in your garden you should take your longitude into account.

Important - to find North (the direction the gnomon points) we do not use a compass. This would tell us magnetic North which is different to true North. The bestway to find true North accurately is by using Polaris.

Also bear in mind that to get an accurate measurement of what time it is we need to take into account the equation of time .


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Solar Eclipsesdemonstrate an understanding that the Moon and Sun appear to be the same size when viewed from Earthdescribe the appearance of partial and total solar eclipsesdescribe, using diagrams, the mechanisms causing solar eclipsesdemonstrate an understanding that the duration of total solar and lunar eclipses are different and that they do not occur every new and full Moon

Occasionally, on our journey around the Earth, the Moon blocks our view of the Sun. It is a remarkable coincidence that both objects are of such a size andat such distances from us that they appear almost exactly the same size to us in the sky. Because the ratio of the distances to the Earth is the same as theratio of their diameters they both take up the same angle, about half a degree, in the sky.

Why eclipses are rare

The diagram below (not to scale) shows that the plane of orbit of the Moon is about 5 degrees to the ecliptical plane which is why solar eclipses do notoccur once a month but are very rare. Nevertheless the Moon in the sky stays close to the ecliptic and passes through the constellations of the zodiac.

Because the Moon does not rotate around the Earth in a plane exactly parallel t o the ecliptical plane this does not occur once every 29 days or so. Solareclipses are actually quite rare. If you get a chance to see a total solar eclipse do your best to do so. They are spectacular and well worth any effort.

have a look at http://www.eclipse.org.uk/ for information about eclipses past, present and future.

Here is an animation of what one sees during a total solar eclipse.

REMEMBER - never observe the Sun directly with any kind of optical instrument. Special glassesmust be worn when observing an eclipse.

1. The Moon partially covers the face of the Sun (first contact to second contact). One can't actuallysee this with the naked eye until the very final stages although it does get noticeably darker andcolder.

2. The diamond ring effect.

3. Totality. At this point, which lasts about a minute, the corona is visible. One may also see Bailey'sbeads. (The last bright flashes of sunlight peaking through the rough lunar surface)

4. Another diamond ring.

5. Partial covering of the Sun as in 1(third to fourth contact).

Topic 1 - Earth, Moon and Sun

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