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A light-year, alternatively spelled light year ( ly or lyr[ 3] ), is a unit of length used to express astronomical distances and is equal to exactly 9,460,730,472,580.8 km ( Scientific notation: 9.4607304725808 × 10 12 km), which is approximately 5.88 trillion mi.
In this calendar, a common year is 365 days (8760 hours, 525 600 minutes or 31 536 000 seconds), and a leap year is 366 days (8784 hours, 527 040 minutes or 31 622 400 seconds). The 400-year civil cycle of the Gregorian calendar has 146 097 days and hence exactly 20 871 weeks.
In recent decades, the average length of a solar day on Earth has been about 86,400.002 seconds [3] (24.000 000 6 hours). There are currently about 365.2421875 solar days in one mean tropical year . Ancient custom has a new day starting at either the rising or setting of the Sun on the local horizon (Italian reckoning, for example, being 24 ...
Distance light travels in one minute – Mercury: 0.39 – Average distance from the Sun – Venus: 0.72 – Average distance from the Sun – Earth: 1.00 – Average distance of Earth's orbit from the Sun (sunlight travels for 8 minutes and 19 seconds before reaching Earth) – Mars: 1.52 – Average distance from the Sun – Jupiter: 5.2 ...
The angular speed of Earth's rotation in inertial space is (7.292 115 0 ± 0.000 000 1) × 10 ^ −5 radians per SI second. [ 35 ] [ n 4 ] Multiplying by (180°/π radians) × (86,400 seconds/day) yields 360.985 6 °/day , indicating that Earth rotates more than 360 degrees relative to the fixed stars in one solar day.
The formal lunar day is therefore the time of a full lunar day-night cycle. Due to tidal locking, this equals the time that the Moon takes to complete one synodic orbit around Earth, a synodic lunar month, returning to the same lunar phase. The synodic period is about 29 + 1 ⁄ 2 Earth days, which is about 2.2 days longer than its sidereal period.
A minute of arc is π 10 800 of a radian . A second of arc, arcsecond (arcsec), or arc second, denoted by the symbol ″, [ 2] is 1 60 of an arcminute, 1 3600 of a degree, [ 1] 1 1 296 000 of a turn, and π 648 000 (about 1 206 264.8) of a radian. These units originated in Babylonian astronomy as ...
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).