PLANET EARTH
1.1Know that the shape of the Earth is an oblate spheroid
A body of revolution formed when an ellipse with minor axis dimension is rotated about its minor axis is
known as an oblate spheroid.
Our Earth is an oblate spheroid. This means that it is a sphere that is slightly squashed at its poles.
1.2Be able to use information about the mean diameter of the Earth
Diameter of the Earth ≈13,000 km
Circumference ≈ 40,840.70 km
Volume of the Earth = 1.15034651 x 1012 km3
1.3 Understand the Earth’s major internal divisions and their features:
a) crust – 30 km thick [Solid – made of iron, oxygen and silicon]
b) mantle – 720 km thick [Solid due to pressure even though rocks are hot enough to melt]
c) outer core – 2,170 km thick [Liquid – made of iron and nickel]
d) inner core – 1,220 km thick [Liquid iron]
1.4 Be able to use the latitude and longitude co-ordinate system
Latitude lines run east-west and are parallel to each other. The further north the point is, the higher the
latitude. Finally, latitude values (Y-values) range between -90 and +90 degrees.
But longitude lines run north-south. They converge at the poles. And its X-coordinates are between -180
and +180 degrees.
Latitude and longitude coordinates make up our geographic coordinate system.
,1.5 Be able to use the major divisions of the Earth’s surface as astronomical reference points, including:
a) Equator – Imaginary line around the middle of a planet or other celestial body. It is exactly halfway
between the poles, at 0o latitude.
b) Tropic of Cancer – Imaginary line placed halfway between the North Pole and the equator at 23 ½ °𝑁. It
is named so because it lies approximately underneath the constellation: Cancer.
c) Tropic of Capricorn – Imaginary line that lies halfway between the South Pole and the Equator at 23
½o S. It is named so because it lies below the constellation: Capricornus
d) Arctic Circle - One of the 2 polar circles and the most northerly of 5 major circles.
e) Antarctic Circle – One of the 2 polar circles and the most southerly of 5 major circles.
f) Prime Meridian – The centre of a geographic coordinate system at which longitude is 0o. [It is like a
vertical equator]
g) North Pole – Point in the Northern Hemisphere where the Earth’s axis meets its surface.
h) South Pole – Point in the Southern Hemisphere where the Earth’s axis meets its surface.
1.6 Understand the effects of the Earth’s atmosphere on astronomical observations, including sky
colour, skyglow (light pollution) and ‘twinkling’ (seeing)
Light pollution is the inappropriate or excessive use of artificial light. It can have a serious environmental
consequence for humans, wildlife and our climate.
The components of light pollution:
Glare – Excessive brightness that causes discomfort
Skyglow – Brightening of night sky over inhabited areas
Light Trespass – Light falling where not intended
Causes of Light Pollution
Light Pollution is a side effect of industrial civilisation. Its
sources include buildings’ exterior lighting, advertising,
commercial properties, offices, factories and other
industries.
Outdoor lighting used at night which is insufficient, overly
bright, poorly targeted and improperly shielded serves as
the main cause.
Why is the sky blue?
As white light passes through our atmosphere, tiny air molecules cause it to scatter. The scattering caused
by tiny air particles increases as the wavelength of the light decreases. Violet and blue light have the
shortest wavelengths and red has the longest. Therefore, blue light is scattered more and the sky appears
blue during the day.
,What is astronomical seeing?
Seeing is an astronomical description of how much celestial objects appear to flicker because of changes
in the refractive index of Earth’s atmosphere. In fact, poor seeing results in the loss of detail and fails to
provide the most accurate astronomical sightings.
LUNAR DISC
2.1 Know the shape of the Moon
The Moon is also an oblate spheroid like the Earth.
2.2 Be able to use information about the mean diameter of the Moon (3500 km)
Diameter - 3,500 km
Surface Area – 38,484,510.01 km2
Circumference – 10995.57 km
Volume – 2.2449292975 x 1010 km3
Mass – 7.35 x 1022 kg
2.3 Be able to recognise the appearance of the principal naked-eye lunar surface formations, including:
Crater Maria Terrae Mountains Rilles
2.4 Understand the structure and origin of the principal naked-eye lunar surface formations, including:
a) Craters – Bowl shapes depressions formed on the moon caused by
meteorites. The moon has thousands of craters, given that it has no
atmosphere or much geological activities that could protect/cover up the
craters after many years.
Most craters are formed when meteorites, comets/asteroids crash into a
surface. Impactors aren’t necessarily spherical in shape, but the shape in
craters come from the force of ejection. Craters can be simple or complex.
b) Maria – Large, dark basaltic (igneous rock formed from the cooling of larva) areas on the Moon, formed
by ancient volcanic eruptions. The Maria covers 17% of the Moon’s surface.
c) Terrae – Collective name for highlands. These are bright areas that are higher on the Moon’s surface
than Maria. They are more hilly, mountainous and brighter than the Maria.
d) Mountains – Lunar Mountains are called massifs and are very similar to the mountains found on Earth.
, e) Valleys – Valleys/Rilles are long depressions on the Moon’s surface. They are unusual because other
features such as craters and rays intersect them midway. They are thought to have formed by ancient lava
flows/ collapsed lava tubes.
2.5 Be able to identify the following features on the lunar disc.
MAP OF MOON AT END OF DOCUMENT
2.6 Be able to use the rotation and revolution (orbital) periods of the Moon
The Moon orbits the Earth once every 27.322 days
It also takes 27 days for the moon to rotate on its axis
2.7 Understand the synchronous nature of the Moon’s orbit
If a body’s rotation period and its revolving period around another body are the same and they happen in
the same direction, the orbit is said to be synchronous.
The Moon has a synchronous orbit – The time it takes to rotate on its axis (27 days) and the time it takes
to revolve around our Earth once (27.322 days) are approximately the same.
2.8 Understand the causes of lunar liberation and its effect on the visibility of the lunar disc
Due to the Synchronous Orbit of the Moon, we should only be able to see the Near Side of the Moon
(50% of the entire surface). However, due to Lunar Liberation, we are able to see a maximum of 59% of
the Moon’s surface over the period of its revolution (An extra 9% of the Far Side is occasionally visible to
us).
Lunar Liberation is a slight north-to-south rocking and an east-to-west wobble of the moon. It is caused by
the elliptical orbit.
Liberation in Latitude
The lunar liberation in latitude is due to the Moon's axis being slightly inclined relative to the Earth's axis.
From our angle we can, at one time, see slightly over the North Pole of the Moon and later in the Lunar
Month, we can see slightly past the South Pole of the Moon.
Liberation in Longitude
Liberation in longitude is an effect of the Moon's varying rate of travel along its slightly elliptical orbit
around the Earth. The Moon travels faster when it is at its perigee, and its slowest at apogee.
Although the Moon always presents us with the same face towards the Earth, due to its rotation and
revolution being tidally locked to the same period, the combined effect of all these different liberations
allows us over time to see some 59% of the Moon's surface.
1.1Know that the shape of the Earth is an oblate spheroid
A body of revolution formed when an ellipse with minor axis dimension is rotated about its minor axis is
known as an oblate spheroid.
Our Earth is an oblate spheroid. This means that it is a sphere that is slightly squashed at its poles.
1.2Be able to use information about the mean diameter of the Earth
Diameter of the Earth ≈13,000 km
Circumference ≈ 40,840.70 km
Volume of the Earth = 1.15034651 x 1012 km3
1.3 Understand the Earth’s major internal divisions and their features:
a) crust – 30 km thick [Solid – made of iron, oxygen and silicon]
b) mantle – 720 km thick [Solid due to pressure even though rocks are hot enough to melt]
c) outer core – 2,170 km thick [Liquid – made of iron and nickel]
d) inner core – 1,220 km thick [Liquid iron]
1.4 Be able to use the latitude and longitude co-ordinate system
Latitude lines run east-west and are parallel to each other. The further north the point is, the higher the
latitude. Finally, latitude values (Y-values) range between -90 and +90 degrees.
But longitude lines run north-south. They converge at the poles. And its X-coordinates are between -180
and +180 degrees.
Latitude and longitude coordinates make up our geographic coordinate system.
,1.5 Be able to use the major divisions of the Earth’s surface as astronomical reference points, including:
a) Equator – Imaginary line around the middle of a planet or other celestial body. It is exactly halfway
between the poles, at 0o latitude.
b) Tropic of Cancer – Imaginary line placed halfway between the North Pole and the equator at 23 ½ °𝑁. It
is named so because it lies approximately underneath the constellation: Cancer.
c) Tropic of Capricorn – Imaginary line that lies halfway between the South Pole and the Equator at 23
½o S. It is named so because it lies below the constellation: Capricornus
d) Arctic Circle - One of the 2 polar circles and the most northerly of 5 major circles.
e) Antarctic Circle – One of the 2 polar circles and the most southerly of 5 major circles.
f) Prime Meridian – The centre of a geographic coordinate system at which longitude is 0o. [It is like a
vertical equator]
g) North Pole – Point in the Northern Hemisphere where the Earth’s axis meets its surface.
h) South Pole – Point in the Southern Hemisphere where the Earth’s axis meets its surface.
1.6 Understand the effects of the Earth’s atmosphere on astronomical observations, including sky
colour, skyglow (light pollution) and ‘twinkling’ (seeing)
Light pollution is the inappropriate or excessive use of artificial light. It can have a serious environmental
consequence for humans, wildlife and our climate.
The components of light pollution:
Glare – Excessive brightness that causes discomfort
Skyglow – Brightening of night sky over inhabited areas
Light Trespass – Light falling where not intended
Causes of Light Pollution
Light Pollution is a side effect of industrial civilisation. Its
sources include buildings’ exterior lighting, advertising,
commercial properties, offices, factories and other
industries.
Outdoor lighting used at night which is insufficient, overly
bright, poorly targeted and improperly shielded serves as
the main cause.
Why is the sky blue?
As white light passes through our atmosphere, tiny air molecules cause it to scatter. The scattering caused
by tiny air particles increases as the wavelength of the light decreases. Violet and blue light have the
shortest wavelengths and red has the longest. Therefore, blue light is scattered more and the sky appears
blue during the day.
,What is astronomical seeing?
Seeing is an astronomical description of how much celestial objects appear to flicker because of changes
in the refractive index of Earth’s atmosphere. In fact, poor seeing results in the loss of detail and fails to
provide the most accurate astronomical sightings.
LUNAR DISC
2.1 Know the shape of the Moon
The Moon is also an oblate spheroid like the Earth.
2.2 Be able to use information about the mean diameter of the Moon (3500 km)
Diameter - 3,500 km
Surface Area – 38,484,510.01 km2
Circumference – 10995.57 km
Volume – 2.2449292975 x 1010 km3
Mass – 7.35 x 1022 kg
2.3 Be able to recognise the appearance of the principal naked-eye lunar surface formations, including:
Crater Maria Terrae Mountains Rilles
2.4 Understand the structure and origin of the principal naked-eye lunar surface formations, including:
a) Craters – Bowl shapes depressions formed on the moon caused by
meteorites. The moon has thousands of craters, given that it has no
atmosphere or much geological activities that could protect/cover up the
craters after many years.
Most craters are formed when meteorites, comets/asteroids crash into a
surface. Impactors aren’t necessarily spherical in shape, but the shape in
craters come from the force of ejection. Craters can be simple or complex.
b) Maria – Large, dark basaltic (igneous rock formed from the cooling of larva) areas on the Moon, formed
by ancient volcanic eruptions. The Maria covers 17% of the Moon’s surface.
c) Terrae – Collective name for highlands. These are bright areas that are higher on the Moon’s surface
than Maria. They are more hilly, mountainous and brighter than the Maria.
d) Mountains – Lunar Mountains are called massifs and are very similar to the mountains found on Earth.
, e) Valleys – Valleys/Rilles are long depressions on the Moon’s surface. They are unusual because other
features such as craters and rays intersect them midway. They are thought to have formed by ancient lava
flows/ collapsed lava tubes.
2.5 Be able to identify the following features on the lunar disc.
MAP OF MOON AT END OF DOCUMENT
2.6 Be able to use the rotation and revolution (orbital) periods of the Moon
The Moon orbits the Earth once every 27.322 days
It also takes 27 days for the moon to rotate on its axis
2.7 Understand the synchronous nature of the Moon’s orbit
If a body’s rotation period and its revolving period around another body are the same and they happen in
the same direction, the orbit is said to be synchronous.
The Moon has a synchronous orbit – The time it takes to rotate on its axis (27 days) and the time it takes
to revolve around our Earth once (27.322 days) are approximately the same.
2.8 Understand the causes of lunar liberation and its effect on the visibility of the lunar disc
Due to the Synchronous Orbit of the Moon, we should only be able to see the Near Side of the Moon
(50% of the entire surface). However, due to Lunar Liberation, we are able to see a maximum of 59% of
the Moon’s surface over the period of its revolution (An extra 9% of the Far Side is occasionally visible to
us).
Lunar Liberation is a slight north-to-south rocking and an east-to-west wobble of the moon. It is caused by
the elliptical orbit.
Liberation in Latitude
The lunar liberation in latitude is due to the Moon's axis being slightly inclined relative to the Earth's axis.
From our angle we can, at one time, see slightly over the North Pole of the Moon and later in the Lunar
Month, we can see slightly past the South Pole of the Moon.
Liberation in Longitude
Liberation in longitude is an effect of the Moon's varying rate of travel along its slightly elliptical orbit
around the Earth. The Moon travels faster when it is at its perigee, and its slowest at apogee.
Although the Moon always presents us with the same face towards the Earth, due to its rotation and
revolution being tidally locked to the same period, the combined effect of all these different liberations
allows us over time to see some 59% of the Moon's surface.
