Glossary
- aphelion
- The point in Earth's orbit where it is farthest from the Sun.
- autumnal equinox
- The point in Earth's orbit where the light part of the day is the same length as the dark, after which the nights get longer.
- calendar year
- The length of the year according to the calendar, always a whole number of days.
- common year
- A solar calendar year with 365 days.
- day
- See solar day.
- generation
- A period of time equal to 33 years, used as the leap year cycle in the Earthian Calendar.
- intercalary
- Refers to an extra day, week or month periodically included in a calendar year in order to maintain synchronicity with the seasonal cycle.
- leap year
- A solar calendar year of 366 days.
- lunar calendar
- A calendar that uses lunations for months, with 12 lunations per calendar year.
- lunation
- The average length of a synodic month, equal to about 29.53 days.
- lunisolar calendar
- A calendar that uses lunations for months, with either 12 or 13 lunations per calendar year.
- month
- A period equal, or approximately equal, to a lunation, with possible lengths of 28 to 31 whole days.
- perihelion
- The point in Earth's orbit where it is closest to the Sun.
- perpetual calendar
- A calendar in which weeks and months are synchronised, and thus each calendar date always occurs on the same day of the week.
- season
- The time between seasonal markers, equal to about ¼ years.
- seasonal marker
- A solstice or an equinox.
- sol
- One martian solar day, equal to about 24 hours and 40 minutes.
- solar calendar
- A calendar that uses a fraction of a year as a month (usually 1/12), and has year lengths of 365 or 366 days.
- solar day
- The time taken for Earth to rotate once on its axis and the Sun to return to the same position in the sky, equal to 24 hours.
- summer solstice
- The point in Earth's orbit where the length of the night has reached a minimum.
- synodic month
- The time for the Moon to orbit Earth and return to the same position with respect to Earth; the time between new moons.
- vernal equinox
- The point in Earth's orbit where the light part of the day is the same length as the dark, after which the nights get shorter.
- vernal equinox year
- The average period between successive northern vernal equinoxes, equal to about 365.2424 days.
- week
- A period of 7 days.
- winter solstice
- The point in Earth's orbit where the length of the night has reached a maximum.
- year
- Usually means calendar year.
