Stars, Nebulae, and Stellar Evolution (Video)

Vocabulary flashcards covering key terms and concepts from the lecture notes on plasma, star formation, stellar evolution, and related astronomy topics.

Plasma

A hot, ionized gas state (fourth state of matter) that is the main form of matter in stars; not a liquid or ordinary gas.

Nebula

A cloud of gas and dust in space where star formation begins; stellar nurseries.

Protostar

A forming star inside a collapsing nebula that has not yet reached core temperatures high enough for hydrogen fusion; energy comes from contraction.

Hydrogen burning

Hydrogen fusion in a star’s core that converts hydrogen into helium and releases energy as heat and light.

Helium burning

Fusion of helium into heavier elements (e.g., carbon) during later stages of stellar evolution.

Main sequence

Stable phase where a star fuses hydrogen in its core and maintains hydrostatic equilibrium.

Jeans mass

Critical mass above which gravity dominates internal pressure, causing a gas cloud to collapse into a protostar.

Hydrostatic equilibrium

Balance between inward gravity and outward gas pressure that yields a stable star.

Red giant

Late-stage, cool, luminous star formed when a low- to medium-mass star exhausts core hydrogen and expands.

Red supergiant

Very massive, cool, luminous late-stage star larger than a red giant.

White dwarf

Dense, Earth-sized remnant of a low- to medium-mass star after it sheds outer layers.

Neutron star

Extremely dense stellar remnant formed when a massive star’s core collapses to neutron degeneracy.

Black hole

Collapsed stellar remnant with gravity so strong that light cannot escape; defined by an event horizon.

Supernova

Explosive end of a massive star’s life; disperses heavy elements and can leave a neutron star or black hole.

Iron core and supernova

Fusion stops at iron in a massive star; core collapses, triggering a supernova.

Planetary nebula

Ejected outer layers of a low- to intermediate-mass star; leaves behind a white dwarf.

Hertzsprung-Russell diagram

Plot of stellar luminosity versus temperature (or color); reveals main sequence, giants, and white dwarfs.

Spectral class (OBAFGKM)

Temperature-based stellar classification from hottest to coolest.

Mnemonic for spectral classes

Common mnemonics (e.g., Oh Be A Fine Girl Kiss Me) to remember O, B, A, F, G, K, M order.

Apparent magnitude

Brightness of a star as seen from Earth; depends on distance and intrinsic luminosity.

Absolute magnitude / luminosity

Intrinsic brightness of a star; brightness it would have at a standard distance of 10 parsecs.

Parsecs

Astronomical distance unit; 1 parsec ≈ 3.26 light-years; used for absolute magnitude and distances.

Luminosity

Total energy radiated by a star per unit time; intrinsic brightness.

Milky Way

Our galaxy; all the stars discussed are in the Milky Way unless stated otherwise.

Constellation

A recognized pattern of stars; 88 officially recognized, e.g., Orion, Ursa Major, Ursa Minor.

Orion’s belt

Three aligned stars in Orion; a prominent and easily recognized asterism in winter skies.

Betelgeuse

A red supergiant star; one of the largest known; a cool, luminous example of late-stage massive stars.

Sirius

Bright star in the sky; known as the Dog Star; linked to the “dog days of summer.”

Pillars of Creation

Hubble image of the Eagle Nebula’s star-forming columns; visible in multiple wavelengths (infrared and optical).

Light pollution

Excess artificial light that obscures faint celestial objects and reduces night-sky visibility.

Dark Sky Initiative (West Texas)

Policy to minimize upward-facing light (floodlights, etc.) and light pollution to improve viewing.

Color-temperature relation in stars

Hotter stars appear blue and cooler stars appear red; color indicates surface temperature.

Blue vs. red star temperatures

Blue = hotter (shorter wavelengths); red = cooler (longer wavelengths).

Stellar colors and luminosity on the H-R diagram

Color (temperature) and luminosity determine a star’s position; main sequence runs across from hot/bright to cool/dim.

Sidera classifications for Sun

The Sun is a G-type star (not the hottest or largest); ~5,200–6,000 K surface temperature.

Sirius vs. white dwarfs

Sirius is a bright star, while white dwarfs are compact, low-luminosity remnants of low- to medium-mass stars.