Viewing the Night Sky: Astronomy Practice Flashcards

This set covers key terminology from the Science 10 Astronomy unit, including celestial coordinates, types of galaxies, stellar life cycles, and evidence for the Big Bang Theory.

Constellation

Groups of stars that form a pattern in the sky, with $88$ recognized constellations viewable from Earth.

Asterism

Smaller groups of stars with similar brightness that form patterns within a larger constellation, such as Orion's belt.

Celestial sphere

An imaginary projector on which all celestial bodies lie, which is dependent on Earth's axial tilt and is cut into a north and a south half at the equator.

Ecliptic

The path of the Sun in our sky relative to other celestial bodies throughout Earth's revolution ($one\,year$).

Retrograde motion

The apparent backward movement of a celestial body during certain times of year, which occurs when Earth passes another planet in their orbit.

Azimuth

The distance travelled from the North along the horizon to a celestial object, always measured as an angle from N-E-S-W.

Altitude

The angular height of the celestial object from the horizon to the object's location in the sky, measured from $0^\circ$ to $90^\circ$.

Galaxy

A large-scale group of stars, gas, and dust that are all bound by gravity; the universe contains hundreds of billions of them.

Spiral Galaxy

A galaxy characterized by a nucleus and spiral arms, containing young stars in the arms, older stars in the nucleus, and more dust in the arms.

Elliptical Galaxy

A galaxy where most stars are old and evenly distributed, containing not a lot of gas and dust.

Star cluster

Smaller groups of stars held together by gravity within a galaxy, classified as globular (close to center) or open (outside center).

Absolute magnitude

The brightness of a star if all stars were an equal distance ($32.6\,light\,years$) from Earth.

Luminosity

The measure of how much energy a star is emitting per second.

Spectral lines

A pattern of colours and absorption lines recorded from star emissions that acts as a "fingerprint" to identify chemical composition.

Big Bang Theory

The theory that the universe began as a single, infinitely hot and dense point that inflated and expanded outward starting $13.8\,billion\,years$ ago.

Doppler effect

The apparent change in wave frequency in relation to a source's relative position and motion.

Blue-shift

Occurs when spectral lines from a star move toward the blue-end of the visible light spectrum because the star is moving toward an observer.

Red-shift

Occurs when spectral lines from a star move toward the red-end of the visible light spectrum because the star is moving further away from an observer.

Cosmic Microwave Background (CMB) Radiation

Longer-wavelength energy detected all around space that originated as high frequency gamma rays during the Big Bang.

Dark matter

The most abundant matter in the universe ($23\%$) that is not visible and does not emit light, but can be detected by its gravitational effects.

Dark energy

A force responsible for allowing the universe to increase in its rate of expansion again, making up approximately $73\%$ of the universe.

James Webb Space Telescope

An space-based observatory launched on December 25th, 2021, that orbits $1.5\,million\,km$ away from Earth at the second Lagrange point ($L2$).

Large Hadron Collider (LHC)

A particle accelerator run by CERN that facilitates the collision of high-energy particles at speeds close to the speed of light.

Hertzsprung-Russell (H-R) Diagram

A graph used to classify stars based on the relationship between their size, surface temperature, and luminosity.

Main sequence

The distinct line on the H-R diagram that runs from blue-hot to red-cool and accounts for $90\%$ of all stars.

Stellar equilibrium

The balance in a star where the inward force of gravity is perfectly offset by the outward pressure from fusion and radiation.

Supernova

A powerful explosion that occurs during the death of intermediate-mass or high-mass stars.

Neutron star

A dense core of material that remains after an intermediate-mass star ($10-20\,solar\,masses$) undergoes a supernova.

Black hole

A core of material packed together so tightly after a high-mass star ($>20\,solar\,masses$) undergoes a supernova that nothing can escape.

Parallax

The apparent change in position of an object against a fixed background when viewed from different lines of sight.