Term | Definition |
Tides | occur because of the pull of gravity of the Moon and the Sun on the Earth's oceans. Because the Moon is closer to the Earth, it has the greatest effect on our tides. There are approximately 2 high tides and 2 low tides every 24 hours. |
Spring tides | Spring tides (often called 'king tides' by fishermen) occur at New Moon and Full Moon when the Sun, the Moon and the Earth are in line. This forms extremely high high-tides and extremely low low-tides. |
Neap tides | Neap tides occur at First Quarter and Last Quarter, when the Sun, the Earth and the Moon are at right angles. This forms quite low high-tides and quite high low-tides. |
Umbra | The Umbra is the darker part of the shadow. |
Penumbra | The Penumbra is the lighter part of the shadow. |
Total Eclipse | Observers on the Earth's surface who are shadowed by the darker umbra would see a total eclipse. |
Partial Eclipse | Observers on the Earth's surface who are shadowed by the lighter penumbra would see a partial eclipse. |
Solar Eclipses | occur sometimes when the Moon passes between the Sun and the Earth at New Moon. The shadow of the Moon falls on the Earth appearing to block out (eclipse) the Sun. The next total solar eclipse is 13th November 2012. |
Lunar eclipse | occur sometimes when the Moon passes on the opposite side of the Earth from the Sun at Full Moon. The Moon passes in the Earth's shadow. It appears dull and can only just be seen. The next total lunar eclipse is 15th April 2014. |
Day & Night Facts | The Earth's rotation causes the change of day and night. |
Day & Night Facts | The Earth rotates on its axis once every 23 hours and 56 minutes. |
Day & Night Facts | The rotation of the Earth is west to east, so the Sun is visible in the eastern sky first. |
Day & Night Facts | The Sun shines only on half of the Earth at any time, so that half the Earth is in daylight and the other half is in darkness. |
Day & Night Facts | The tilt on the Earth's axis causes day and night to be of different lengths in different parts of the world. |
Solstice | occurs twice a year. The summer solstice is the longest day (and shortest night) of the year. The winter solstice is the shortest day of the year. |
Equinox | occurs twice a year when day and night are of equal length |
Season Facts | Seasons are caused by the Earth's revolution around the Sun and the unchanging tilt of the Earth's axis. |
Season Facts | The different distances to the Sun caused by the tilt do not cause the seasons. |
Season Facts | The season depends on how much of the Earth's surface is covered by light rays, and at what angle they reach the Earth's surface. |
Season Facts | Head-on rays on a small area are strong and cause summer seasons. Slanting rays focusing on a large area are weaker and cause winter seasons. |
Constellation | A constellation is a group of stars that form an imaginary pattern. |
Zodiac Constellation | The constellations of the zodiac are those groups of stars that travel directly overhead, following the same path as our Sun. Examples of the zodiac constellations are Taurus the Bull, Leo the Lion and Scorpius the Scorpion. |
Elevation | the number of degrees a star is above the horizon |
Azimuth | the number of degrees a star is along the horizon |
Movement of Sun | Our Sun, which is a star, appears to move across the sky from east to west. It appears to move directly overhead along a path called the zenith. This apparent motion is because the Earth is actually rotating in the opposite direction from west to east. |
Movement of Stars | In the northern hemisphere, stars appear to rotate around a central point in the sky called the North Celestial Pole where the Pole Star is. The North Celestial Pole is directly above the North Pole. |
Movement of Stars | In the southern hemisphere, stars appear to rotate around an imaginary point in the sky called the South Celestial Pole. The South Celestial Pole is directly above the South Pole. |
Universe Definition | The universe is all the heavenly bodies such as stars and planets and the enormous space between them. |
Galaxy Definition | Galaxies are collections of hundreds of stars around a common centre. |
Irregular Galaxy | overall globular shape |
Elliptical Galaxy | egg-shaped |
Spiral Galaxy | spiral shape; most common form of galaxy; examples are our Milky Way Galaxy and the Andromeda Galaxy |
The Sun Cycle | Our sun is a star, composed mostly of hydrogen and helium. |
The Sun Cycle | The sun is at the center of our solar system. Planets revolve around the sun. |
The Sun Cycle | The sun is about 150 million kilometers from Earth. This is a distance of one astronomical unit. Light from the sun takes only a few minutes to reach the Earth. |
The Sun Cycle | The sun's temperature varies from 5 500 °C at the surface to 13 600 000 °C at the core. |
The Sun Cycle | The sun rotates approximately every 28 days. |
The Sun Cycle | Sunspots are darker, cooler parts of the sun which rotate approximately every 11 years. |
The Sun Cycle | Solar Flares are explosions of hot gases from the surface. These sendoff electromagnetic radiation that causes auroras in Earth's night sky, and disrupts radio transmission. |
The Sun Cycle | Solar Prominences are arches of hot gases that are seen on the sun's surface. |
The Sun Cycle | The sun makes its energy from nuclear reactions called Nuclear Fusion, a process in which 2 hydrogen nuclei join to make a larger helium nucleus. This process gives off huge amounts of heat and light energy. |
The Sun Cycle | The sun's age is about 4.5 billion years. There is probably enough hydrogen to fuel nuclear fusion reactions for another 5.5 billion years. |
The Moon Cycle | Has a nearly circular orbit around the Earth |
The Moon Cycle | Reflects light from the Sun |
The Moon Cycle | No atmosphere so all UV rays from the Sun reach the surface |
The Moon Cycle | Gravity is only 1⁄6 of the Earth's gravity |
The Moon Cycle | Craters are deep depressions on the surface caused by meteorites |
The Moon Cycle | Maria (or 'seas') are large smooth areas on the surface covered by plains of grey basalt - |
The Moon Cycle | Earth's moon is only the 5th largest moon in the solar system. |
Phases of the Moon | 'Moonlight' - The Moon does not make its own light. It reflects light from the Sun. Half the Moon is always in sunlight, just as half the Earth has 'day' and the other half has 'night'. From Earth, we can only see 50% of the Moon at any time. |
Phases of the Moon | 8 Moon Phases each Lunar Month of 27.3 days |
New Moon | The face of the Moon facing Earth is completely in shadow ('No Moon'). The Sun, the Moon and the Earth are in line. |
Waxing Crescent | A horn-shaped part of the Moon is illuminated. |
First Quarter | Only half of the face of the Moon facing Earth is illuminated |
Waxing Gibbous | More than half of the face we see is illuminated. |
Full Moon | All of the face we see is illuminated. The Sun, the Earth and the Moon are in a line. |
Waning Gibbous | More than half of the face we see appears lit. |
Last Quarter | Only half of the face we see appears lit. |
Waning Crescent | A horn-shaped part of the Moon facing Earth is illuminated |