SCIENCE
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What is astronomy?
The scientific study of space and celestial objects.
What is a celestial object?
A natural object in space such as a planet, moon or star.
What is an axis?
An imaginary line around which an object rotates.
What is an orbit?
The curved path of an object moving around another due to gravity.
What is latitude?
Angular distance north or south of the Equator.
What is longitude?
Angular distance east or west of the Prime Meridian.
What is the Equator?
The line of 0° latitude dividing Earth into Northern and Southern Hemispheres.
What is the Prime Meridian?
The line of 0° longitude passing through Greenwich, England.
Which way do lines of latitude run?
East–west, parallel to the Equator.
Which way do lines of longitude run?
North–south, meeting at the poles.
What is the celestial sphere?
An imaginary sphere on which celestial objects appear to be located.
What is the North Celestial Pole?
The point in the sky in the direction of Earth’s north rotational axis.
What is the South Celestial Pole?
The point in the sky in the direction of Earth’s south rotational axis.
What is the Celestial Equator?
The projection of Earth’s Equator onto the celestial sphere.
What is azimuth?
Compass direction measured clockwise from north, from 0° to 360°.
What is elevation?
Angle above the horizon; 0° at the horizon and 90° overhead.
What is the zenith?
The point directly overhead.
What is the nadir?
The point directly beneath the observer.
What azimuth is east?
90°.
What azimuth is south?
180°.
What azimuth is west?
270°.
What is rotation?
An object spinning around its own axis.
What is revolution?
An object travelling around another object in an orbit.
How long is an average solar day?
About 24 hours.
How long does Earth take to orbit the Sun?
About 365.25 days.
Name the eight planets in order from the Sun.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
What is the largest planet?
Jupiter.
What is the smallest planet?
Mercury.
What is the hottest planet?
Venus.
What objects are in the solar system?
The Sun, eight planets, dwarf planets, moons, asteroids, comets and other small bodies.
Which planets are terrestrial?
Mercury, Venus, Earth and Mars.
Which planets are giants?
Jupiter, Saturn, Uranus and Neptune.
How do terrestrial planets differ from giant planets?
They are smaller, mostly rock and metal, and closer to the Sun.
Which are the gas giants?
Jupiter and Saturn.
Which are the ice giants?
Uranus and Neptune.
What causes day and night?
Earth’s rotation turns locations towards and away from the Sun.
Why does the Sun appear to rise in the east?
Earth rotates eastward, making the Sun appear to move westward.
What causes sunset?
Your location rotates away from the Sun.
How far is Earth’s axis tilted?
About 23.5° from perpendicular to its orbital plane.
Why are summer days longer?
The hemisphere tilted towards the Sun spends more time in daylight each rotation.
Why are winter days shorter?
The hemisphere tilted away from the Sun spends less time in daylight.
Why are seasons opposite in the two hemispheres?
When one hemisphere tilts towards the Sun, the other tilts away.
Why do stars appear to move across the sky each night?
Earth rotates on its axis.
In which direction do stars generally appear to move?
From east to west.
What is a sidereal day?
One Earth rotation relative to distant stars, about 23 hours 56 minutes.
Why do stars appear to circle the celestial poles?
Earth’s rotation makes stars appear to trace circles around the directions of its axis.
Which pole do stars circle in the Northern Hemisphere?
The North Celestial Pole.
Which pole do stars circle in the Southern Hemisphere?
The South Celestial Pole.
Which star is close to the North Celestial Pole?
Polaris.
Which way do stars appear to circle the South Celestial Pole when facing it?
Clockwise.
Which way do stars appear to circle the North Celestial Pole when facing it?
Anticlockwise.
How long is a sidereal month?
About 27.3 days.
What is a sidereal month?
One Moon orbit relative to distant stars.
How long is a synodic month?
About 29.5 days.
What is a synodic month?
Time from one Moon phase to the same phase again.
Why is the synodic month longer?
Earth moves along its orbit, so the Moon must travel farther to realign with the Sun.
How much longer is a synodic month?
About 2.2 days.
What causes Moon phases?
We see changing fractions of the Moon’s sunlit half as it orbits Earth.
Does the Moon make its own light?
No; it reflects sunlight.
List the eight Moon phases in order.
New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, Waning Crescent.
What does waxing mean?
The visible illuminated fraction is increasing.
What does waning mean?
The visible illuminated fraction is decreasing.
What is a gibbous Moon?
More than half but not all of the visible face is lit.
What is a crescent Moon?
Less than half of the visible face is lit.
Why do eclipses not happen every month?
The Moon’s orbit is tilted about 5° to Earth’s orbital plane, so the bodies usually miss exact alignment.
What are lunar nodes?
Where the Moon’s orbital plane crosses Earth’s orbital plane.
When can an eclipse happen?
When a new or full Moon occurs near a lunar node.
What is the alignment for a solar eclipse?
Sun–Moon–Earth.
What is the alignment for a lunar eclipse?
Sun–Earth–Moon.
At which Moon phase can a solar eclipse happen?
New Moon.
At which Moon phase can a lunar eclipse happen?
Full Moon.
What is the umbra?
The darkest central part of a shadow.
What is the penumbra?
The lighter outer part of a shadow.
What is a solstice?
A time when the Sun reaches its northernmost or southernmost apparent position in the sky.
What is an equinox?
A time when the Sun crosses the celestial equator and day and night are nearly equal in length.
When is the Southern Hemisphere summer solstice?
Around 21–22 December.
When is the Southern Hemisphere winter solstice?
Around 20–21 June.
What happens at the North Pole near the June solstice?
24-hour daylight.
What happens at the South Pole near the June solstice?
24-hour darkness.
What happens at the South Pole near the December solstice?
24-hour daylight.
What happens at the North Pole near the December solstice?
24-hour darkness.
How long are day and night around an equinox at most locations?
Approximately 12 hours each.
What happens at the poles around equinox?
The Sun transitions between the long polar day and polar night.
In which direction does Earth rotate?
West to east.
How does Earth orbit the Sun viewed from above the North Pole?
Anticlockwise.
How does the Moon orbit Earth viewed from above the North Pole?
Anticlockwise.
Why do we usually see the same lunar face?
The Moon rotates once in about the same time it orbits Earth (synchronous rotation).
Name the 12 traditional Zodiac constellations.
Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces.
Which Zodiac constellation is the lion?
Leo.
Which is the bull?
Taurus.
Which is the twins?
Gemini.
Which is the scorpion?
Scorpius.
Which is the crab?
Cancer.
Which 13th constellation also lies along the ecliptic?
Ophiuchus.
What is the ecliptic?
The Sun’s apparent yearly path across the celestial sphere.
Why does the Sun appear to move through Zodiac constellations?
Earth’s revolution changes the Sun’s apparent position against background stars.
Why do we see different constellations at night across the year?
As Earth orbits the Sun, its night side points towards different parts of space.
How long does the Sun take to appear to travel around the Zodiac?
About one year.