CARA'S TIPSThe earth as a planet: rotation, revolution, latitude & longitude
JAMBWAECNECO
What the syllabus asks
JAMB: Physical Geography A: the earth in the solar system, rotation and revolution; the shape and size of the earth; latitudes and distances, longitudes and time
WAEC: Elements of Physical Geography: the earth as a planet in relation to the sun; latitude and distance; longitude and time; the earth’s rotation and revolution and their effects
NECO: Elements of Physical Geography: the earth as a planet in relation to the sun; latitude and distance; longitude and time; the earth’s rotation and revolution and their effects
What you will learn
- Describe the solar system and the position of the earth in it.
- State the shape and size of the earth and give proofs of its shape.
- Explain rotation and its effects, and revolution and its effects.
- Explain equinoxes, solstices, seasons and variations in day length, and calculate the noon altitude of the sun.
- Define latitude and longitude and name the important lines.
- Calculate distances along meridians and parallels.
- Calculate local times from longitude, and explain standard time and the International Date Line.
Key points
- The solar system has eight planets; the earth is the third, about 150 million km from the sun.
- The earth is an oblate spheroid; proofs include ships at sea, circumnavigation, eclipse shadows and satellite photos.
- Rotation (24 h, west to east) causes day and night, time differences, deflection of winds (Coriolis) and tides.
- Revolution (365¼ days) with a 23½° tilt causes seasons, changing day length and the movement of the overhead sun.
- Equinoxes about 21 March and 23 September; solstices about 21 June (Cancer) and 22 December (Capricorn).
- Noon altitude = 90° − latitude difference between the place and the overhead sun.
- Latitude: angular distance N or S of the equator; 1° ≈ 111 km along a meridian.
- Distance along a parallel = Δλ/360 × 2πR cos θ.
- Longitude: 0°–180° E or W of Greenwich; 15° = 1 hour, 1° = 4 minutes.
- East is ahead, west is behind; Nigeria uses WAT = GMT + 1.
- The International Date Line (≈180°): eastward repeat a day, westward skip a day.
- Solar eclipse at new moon (moon in the middle); lunar eclipse at full moon (earth in the middle).
Start here: The earth in the solar system
When you look up at the night sky over Maiduguri or Port Harcourt, you are looking out from one small planet in a family of bodies held together by the gravity of a star: the sun.
The eight planets in order from the sun
A memory aid: "My Very Educated Mother Just Served Us Noodles". Mercury, Venus, Earth and Mars are the small, rocky inner (terrestrial) planets; Jupiter, Saturn, Uranus and Neptune are the large outer (giant) planets, made mostly of gases and ices. Jupiter is the largest; Mercury the smallest and nearest the sun. In 2006 the International Astronomical Union reclassified Pluto as a dwarf planet, so older textbooks that list nine planets are out of date.
The earth’s special position
- It is the third planet, at an average distance of about 150 million km from the sun.
- This distance gives temperatures at which water can exist as a liquid. With an atmosphere containing oxygen and a protective ozone layer, the earth is the only planet known to support life.
- It has one natural satellite, the moon, which revolves around it in about 29½ days (from new moon to new moon) and causes tides.
Light travels at about 300,000 km per second. Using 150 million km for the sun–earth distance, roughly how long does sunlight take to reach the earth?
- Time = distance ÷ speed = 150,000,000 ÷ 300,000 = 500 seconds.
- 500 ÷ 60 = 8.3 minutes.
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Practice questions
- Mercury
- Venus
- Mars
- Earth
Show answer
A: Mercury
Order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- Saturn
- Neptune
- Earth
- Jupiter
Show answer
D: Jupiter
Jupiter is the largest of the eight planets.
- north to south
- south to north
- west to east
- east to west
Show answer
C: west to east
This is why the sun appears to rise in the east.
- 29½ days
- 24 hours
- 365¼ days
- 12 hours
Show answer
B: 24 hours
Rotation causes day and night.
- change of seasons
- day and night
- the rising and setting of the sun
- deflection of winds
Show answer
A: change of seasons
Revolution plus the tilted axis gives the seasons.
Key words
- Solar system
- The sun and all the bodies that orbit it: planets, dwarf planets, moons, asteroids and comets.
- Planet
- A large body that orbits the sun and has cleared its orbit of other bodies.
- Oblate spheroid
- A sphere slightly flattened at the poles and bulging at the equator; the shape of the earth.
- Axis
- The imaginary line through the North and South Poles around which the earth rotates.
- Rotation
- The spinning of the earth on its axis, once in about 24 hours.
- Revolution
- The movement of the earth around the sun in its orbit, once in about 365¼ days.
- Equinox
- A day when the sun is overhead at the equator at noon and day and night are equal everywhere (about 21 March and 23 September).
- Solstice
- A day when the overhead sun reaches its furthest north (Tropic of Cancer, about 21 June) or south (Tropic of Capricorn, about 22 December).
- Latitude
- The angular distance of a place north or south of the equator.
- Parallel
- A line of latitude; a small circle parallel to the equator (the equator itself is a great circle).
- Longitude
- The angular distance of a place east or west of the Prime (Greenwich) Meridian.
- Meridian
- A line of longitude, a half great circle from pole to pole.
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