Astro Quiz Study Guide Definitions and Light

The Celestial Sphere

  • An imaginary sphere of infinite radius centered on Earth, displaying celestial bodies.

  • North/South Celestial Pole: Points that the Earth's axis extends into space.

  • Celestial Equator: Projection of Earth's equator onto the celestial sphere.

The Ecliptic

  • The apparent path of the Sun through the sky over a year, where the Earth orbits around the Sun.

  • Vernal Equinox: Sun crosses the celestial equator from south to north, marking the beginning of spring in March.

  • Autumnal Equinox: Sun enters the Southern hemisphere in September.

Right Ascension (RA)

  • The celestial equivalent of longitude.

  • Measured in hours, minutes, and seconds.

  • Zero hour RA is at the vernal equinox.

Declination

  • The celestial equivalent of latitude in the equatorial coordinate system.

  • Measured in degrees north/south of the celestial equator.

Solstices

  • Summer Solstice: Occurs in June when the Sun is over the Tropic of Cancer.

  • Winter Solstice: Occurs in December when the Sun is over the Tropic of Capricorn.

Dark Energy

  • Hypothetical energy accounting for the accelerating expansion of the universe.

  • First introduced by Einstein as the "cosmological constant" in 1917.

Dark Matter

  • Comprises approximately 85% of the universe's mass.

  • Not directly observable; inferred by gravitational effects.

Molecular Clouds

  • Cold, dense regions composed of dust and hydrogen gas where stars form.

Black Holes

  • Stellar Black Hole: Formed from the gravitational collapse of a star.

  • Supermassive Black Hole: Found at centers of galaxies, with mass millions to billions of times that of the Sun.

Planets and Dwarf Planets

  • Planet: Orbits a star, rounded by its own gravity, and has cleared its orbit of debris.

  • Dwarf Planets: Orbit the Sun but have not cleared their orbital paths; includes Pluto, Ceres, and Eris.

Trans-Neptunian Objects (TNOs)

  • Objects orbiting the Sun beyond Neptune; many located in the Kuiper Belt.

Small Solar System Bodies

  • Objects not classified as planets or their moons, including comets and asteroids.

Eclipses and Transits

  • Eclipse: When one celestial body obscures another.

  • Transit: When a smaller body passes in front of a larger one.

Astronomical Unit (AU)

  • A standard unit for measuring distances in the Solar System; approximately 149.6 million kilometers.

Parallax and Parsec

  • Parallax: Apparent shift in position of a nearby star due to Earth's movement.

  • 1 parsec = 3.26 light-years, measured using parallax angle.

Luminosity

  • Amount of light emitted by a star.

The Nature of Light

  • Light acts as both a wave and a particle (photon); explained by Einstein's photoelectric effect.

Spectroscopy

  • The study of the interaction of light with matter, used to determine an object's composition and distance.

Chromatic and Spherical Aberration

  • Chromatic Aberration: Different wavelengths of light refracted differently.

  • Spherical Aberration: Lens imperfections causing blurred images.

Telescopes

  • Refracting Telescopes: Use lenses to gather light.

  • Reflecting Telescopes: Use mirrors; avoid chromatic aberration.

Mounting Systems for Telescopes

  • Alt-Azimuth Mount: Simpler design, not aligned with Earth’s axis.

  • Equatorial Mount: Aligned with Earth's rotational axis, allows tracking of celestial objects.

  • Dobsonian Mount: A simple, affordable design popularized by amateur astronomers.

Binoculars

  • Comprise two aligned telescopes for depth perception.

  • Porro Prism Binoculars: Wide-field, uses prism design.

  • Roof Prism Binoculars: More compact, requires precise alignment.