MYP Physics Astrophysics Key Definitions

A model of the universe in which space has been expanding from a very hot, very dense early state, leading to the cooler, structured universe observed today.

A constellation is a recognized pattern of stars as seen from Earth.

Electromagnetic radiation filling space, observed today mainly as microwaves, interpreted as cooled and stretched light released when the early universe became transparent.

The Doppler effect is the change in observed wavelength or frequency of a wave due to relative motion between the source and the observer.

A solar-system object that orbits the Sun and is nearly round due to its own gravity, but has not cleared the neighborhood around its orbit.

In a geocentric model, a small circular motion of a planet whose center itself moves on a larger circle around Earth, used to reproduce observed planetary motions.

An exoplanet is a planet that orbits a star outside the Solar System.

A galaxy is a vast system of stars and matter held together by gravity.

A model of the solar system in which Earth is at the center and the Sun, Moon, planets, and stars move around Earth.

A model of the solar system in which the Sun is central and the planets (including Earth) orbit the Sun.

Hubble’s law states that the speed at which a galaxy moves away from us is proportional to its distance from us.

A lunar eclipse occurs when the Earth is between the Sun and the Moon.

An orbit is a circular or elliptical path followed by an object as it moves around another object in space.

An object that orbits the Sun, is massive enough to be nearly round due to its own gravity, has cleared the neighborhood around its orbit, and is not massive enough to sustain nuclear fusion.

Red shift is the increase in wavelength of light from an object moving away from the observer.

The apparent temporary reversal of a planet’s motion across the sky relative to the background stars.

A natural object that orbits a larger body due to gravity, such as the Moon orbiting Earth.

A representation of a system or process used to explain observations and make predictions, often with known limitations.

The Sun and all objects that orbit it or are otherwise gravitationally bound to it, including planets, moons, dwarf planets, asteroids, comets, and dust.