UPCAT REVIEWER SCIENCE (copy)

Universe

The vast gaseous space where galaxies, stars, planets, moons, and other heavenly bodies are suspended and move with perfect orderliness.

Democritus

Pioneered the concept of the Milky Way, proposing it was composed of thousands of unresolved stars.

Plato

Viewed the universe as perfect and unchanging, reasoning that the most perfect orbit of a planet is circular with constant motion.

Thales

Believed that everything comes out of water and that Earth floats on water.

Celestial sphere

An ancient concept that Earth was enclosed in a rotating sphere with stars as fixed points; proposed by Anaximenes.

Big-bang Theory

A theory proposed by Edwin Hubble that posits the universe originated from an extremely hot and dense fireball called YLEM and is expanding.

Steady State Theory

A theory suggesting the universe has no beginning or end, with new materials continuously produced as galaxies recede.

Oscillating Universe Theory

Proposed by Fred Hoyle, suggesting the universe expands like the Big Bang theory but its expansion eventually halts due to gravitational attraction.

Planetisimal Theory

The theory that the sun collided with another star leading to the formation of the solar system.

Companion Star Theory

The theory that the sun had a companion star that exploded after colliding with the sun.

Nebular Hypothesis

The theory that the universe came from a saucer-shaped nebula which cooled and began to spin in space.

Solar system

The system comprising the sun and all celestial bodies that revolve around it.

Ptolemaic System

An Earth-centered (Geocentric) model of the universe.

Copernican System

A sun-centered (heliocentric) model of the universe.

Kepler’s First Law

Planets orbit the sun in elliptical paths.

Kepler’s Second Law

A planet moves more rapidly when closer to the sun.

Kepler’s Third Law

The ratio of the cube of a planet’s average distance from the sun to the square of its orbital period is constant.

Moon

Earth’s satellite, approximately 384,000 km away, with a diameter of 1/4 that of Earth.

Solar Eclipse

A phenomenon when the moon partially or totally hides the sun as it aligns between the sun and Earth.

Lunar Eclipse

A phenomenon when the Earth casts a shadow on the moon, causing partial or total obscuration.

Apogee

The point in the Moon's elliptical orbit when it is farthest from Earth.

Perigee

The point in the Moon's elliptical orbit when it is closest to Earth.

Synodic month

The time it takes for the Moon to complete a cycle of phases, approximately 29.5 days.

Sidereal rotation

The time it takes for the Moon to fully rotate on its axis relative to the stars, which is about 27.3 days.

Umbra

The darkest part of a shadow cast during an eclipse.

Penumbra

A partial outer shadow that is lighter than the inner shadow (umbra) during an eclipse.

Diurnal motion

The apparent daily motion of stars and other celestial bodies due to the Earth's rotation.

Annual motion

The apparent shift in the positions of the stars relative to the sun over the course of a year due to Earth's revolution.

Precession

The westward motion of the equinoxes along the ecliptic, caused by a gradual shift in the orientation of Earth's axis.

Equinox

A day with equal durations of day and night, occurring twice a year.

Solstice

A day with either the longest day or the shortest, occurring twice a year.

Galaxies

Groups of billions of stars along with their planets, gases, and dust held together by gravity.

Neutron star

A very dense, compact mass of neutrons resulting from the collapse of a star under its own gravity.

Black holes

Regions in space with such strong gravitational pull that no matter or energy can escape.

Asteroid

An irregularly shaped rock that orbits the Sun, typically found in the asteroid belt between Mars and Jupiter.

Comet

An astronomical object made of ice and dust with a tail produced by vaporization when close to the Sun.

Meteor

A mass of rock from space that burns up upon entering Earth's atmosphere.

Meteorite

A piece of rock that has reached Earth's surface from outer space.

Meteoroids

Rocky fragments in space that become meteors when entering Earth’s atmosphere.