Paper 1 Astronomy

Oblate Spheroid

The true shape of the Earth; a sphere that is slightly flattened at the poles and bulges at the equator.

Crust

The thin

Mantle

The thick layer of hot

Outer Core

A liquid layer composed of iron and nickel that lies beneath the Earth's mantle.

Inner Core

The solid

Latitude

The coordinate system measuring angular distance north or south of the Earth's equator.

Longitude

The coordinate system measuring angular distance east or west of the Prime Meridian.

Equator

The imaginary line of latitude wrapping around the Earth's middle at 0 degrees.

Prime Meridian

The line of longitude passing through Greenwich

Tropics of Cancer and Capricorn

The latitudes 23.5 degrees North and 23.5 degrees South where the Sun can appear directly overhead.

Arctic and Antarctic Circles

The latitudes 66.5 degrees North and 66.5 degrees South marking the boundaries of polar day and night.

Skyglow

The brightening of the night sky caused by artificial light pollution

Twinkling (Seeing)

The apparent rapid shifting or shimmering of a star's light caused by turbulence in Earth's atmosphere.

Maria

Dark

Terrae

Light-coloured

Lunar Craters

Bowl-shaped depressions formed on the Moon's surface by high-velocity meteorite impacts.

Synchronous Orbit

An orbit where a body takes the exact same time to rotate once on its axis as it does to revolve around its parent body.

Libration

The apparent wobbling or rocking motion of the Moon that allows observers on Earth to see about 59% of its surface over time.

Precession

The slow

Spring Tide

An exceptionally high or low tide occurring during a New or Full Moon when the Sun and Moon pull in alignment.

Neap Tide

A moderate tide with the least difference between high and low water

Umbral Contact

The specific moments marking the phases of an eclipse as a body moves into and out of the deepest central shadow.

Annular Solar Eclipse

An eclipse where the Moon covers the Sun's center but leaves its outer edges visible as a ring of fire.

Sidereal Day

The time taken for Earth to rotate exactly 360 degrees on its axis relative to distant stars (23 hours 56 minutes).

Synodic (Solar) Day

The time taken for Earth to rotate on its axis relative to the Sun

Apparent Solar Time (AST)

Time measured directly by the actual position of the Sun in the sky (sundial time).

Mean Solar Time (MST)

Time based on a fictional uniformly moving Mean Sun to create reliable

Equation of Time

The calculation used to adjust sundial time to clock time

Sidereal Month

The time it takes the Moon to complete one full 360-degree orbit around the Earth relative to the stars (27.3 days).

Synodic Month

The time taken for the Moon to cycle through all its phases from New Moon to New Moon (29.5 days).

Solstice

The two times of year (summer and winter) when the Sun reaches its highest or lowest point in the sky at noon.

Equinox

The two times of year (spring and autumn) when night and day are of equal length everywhere on Earth.

Ecliptic

The apparent annual path of the Sun across the celestial sphere against the background of stars.

Zodiacal Band

The narrow 16-degree wide region of the sky centered on the ecliptic where the planets and Moon are always found.

Retrograde Motion

The apparent temporary westward backward motion of a planet against the stars as Earth overtakes it.

Radiant

The specific point in the night sky from which meteors in a particular shower appear to originate.

Conjunction

An event where two celestial bodies line up or appear very close together in the sky.

Opposition

When an outer planet is directly opposite the Sun from Earth

Elongation

The angular separation between the Sun and an inner planet (Mercury or Venus) as viewed from Earth.

Transit

When a smaller celestial body passes directly across the face of a larger body

Occultation

When a closer celestial body passes completely in front of a more distant body

Celestial Sphere

An imaginary giant sphere surrounding Earth onto which all deep-space objects can be mapped.

Horizon Coordinate System

A system locating objects using Altitude (angle above horizon) and Azimuth (compass direction).

Equatorial Coordinate System

A system locating objects using Declination (like latitude) and Right Ascension (like longitude).

Zenith

The imaginary point in the sky directly above an observer's head.

Nadir

The imaginary point in the sky directly below an observer's feet.

Meridian (Celestial)

An imaginary line running from North to South through the observer's zenith

Circumpolar Stars

Stars that never set below the horizon from a given latitude due to their proximity to the celestial pole.