Core astrophysics concepts such as redshift, light-years, stellar classification, and gravitational lensing explained in plain language. Front: the concept. Back: a plain-language explanation.
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- Redshift
- The shift of light toward the red end of the spectrum when an object moves away from us, caused by the Doppler effect.
- Blueshift
- The shift of light toward the blue end of the spectrum when an object moves toward us, caused by the Doppler effect.
- Light-year
- The distance light travels through empty space in one year, equal to about 5.88 trillion miles or 9.46 trillion kilometers.
- Parallax
- The apparent shift in position of a nearby star when viewed from opposite sides of Earth's orbit around the Sun, used to measure stellar distances.
- Apparent magnitude
- How bright a star appears from Earth, as measured by the naked eye or telescopes.
- Absolute magnitude
- The intrinsic brightness of a star if it were placed at a standard distance of 10 parsecs (32.6 light-years) from Earth.
- Luminosity
- The total amount of energy a star radiates per unit time, measured in watts.
- Hertzsprung-Russell diagram
- A scatter plot of stars showing the relationship between their luminosity and surface temperature, revealing stellar properties and life stages.
- Spectral classification
- A system categorizing stars by their surface temperature and spectrum using letters O, B, A, F, G, K, M, from hottest to coolest.
- Main sequence
- The long-lived phase of a star's life when it fuses hydrogen in its core, represented as a diagonal band on the Hertzsprung-Russell diagram.
- White dwarf
- A dense remnant of a star after it has shed its outer layers, about the size of Earth but with the mass of the Sun, slowly cooling over time.
- Red giant
- A large, cool, reddish star in the late stage of stellar evolution, formed when a star exhausts hydrogen fuel and expands.
- Neutron star
- An extremely dense stellar remnant composed almost entirely of neutrons, typically 20 kilometers in diameter but with the mass of the Sun.
- Black hole
- A region of spacetime where gravity is so extreme that not even light can escape from beyond the event horizon.
- Event horizon
- The boundary around a black hole from which no object or light can escape, even at the speed of light.