Units

Units

DISTANCES IN ASTRONOMY

  • Astronomical Unit (AU): A unit commonly used to measure distances within the solar system, equivalent to the average distance between the Earth and the sun, approximately 150 million km.

  • Light-year: The distance that light travels in one year, approximately 9.461 trillion km. It’s used to measure larger, interstellar distances.

  • Parsec (pc): This is equal to approximately 3.26 light-years, or 31 trillion km. It’s often used by astronomers to measure distances to galaxies and other extra-galactic objects.

TIME PERIODS IN ASTRONOMY

  • Sidereal period: The time it takes for an object in the sky to return to the same position relative to the stars.

  • Synodic period: The time it takes for an object in the sky to return to the same position relative to the sun.

  • Gigayear (Gyr): A unit of time equal to one billion years, used in cosmological contexts.

PHYSICAL PROPERTIES AND MEASUREMENTS IN ASTRONOMY

  • Magnitude: A logarithmic measure of the brightness of an object in a specific wavelength or passband, often in the visible or infrared spectrum.

  • Spectral class: A classification system for stars based on their spectral characteristics.

  • Absolute magnitude: The brightness of a celestial object as it would appear if it were at a standard distance away from the viewer.

  • Apparent magnitude: The brightness of a celestial object as seen by a viewer on Earth.

  • Redshift: The shift of light to longer wavelengths (the red end of the spectrum) due to the motion of the source away from the observer. It can be used to calculate the velocity and distance of galaxies.

FORCE AND ENERGY IN ASTRONOMY

  • Gravity (g): The force that attracts a body toward the centre of the Earth, or toward any other physical body having mass. It’s responsible for keeping the planets in their orbits around the sun.

  • Solar luminosity (L): The standard unit of power in astronomy, used to quantify the energy output of stars.

  • Electromagnetic spectrum: The range of wavelengths or frequencies over which electromagnetic radiation extends, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Remember to ensure understanding, calculation and conversion of these units, as they’ll form a crucial part of your astrophysics revision.