which length of year is a light year calculated on, sidereal or solar?

Answer 1

The definition is to use a Julian year, which is 365.25 days. Which year is to be used however, is not a settled issue, as the text in the link provided indicates

Now, given that the difference between a Julian year, a sidereal and a solar one accounts for a variation of less than 0.004%, and that light year measurement typically have a much larger uncertainty, the point of which year to use is rather moot.

Answer 2

You are thinking of sidereal and solar *days* not years. The length of time it takes for the earth to make one orbit is 365.25 solar days and is *also* 366.25 sidereal days. The point is that the sidereal day is about 4 minutes shorter than a solar day. The year is the same either way. That is the time used for the lightyear.

It should be pointed out that we can't measure such distances to the .3% accuracy that would be needed even if there were a difference betwen the two years.

Answer 3

An apparent sidereal day is the time it takes for the Earth to turn 360 degrees in its rotation; more precisely, is the time it takes a typical star to make two successive upper meridian transits. This is slightly shorter than a solar day. There are 366.2422 sidereal days in a tropical year, but 365.2422 solar days, resulting in a sidereal day of 86,164.091 seconds (or: 23 hours, 56 minutes, 4.091 seconds).

The reason there is one more sidereal day than "normal" days in a year is that the Earth's orbit around the Sun offsets one sidereal day, giving observers on Earth 365 1/4 days, even though the planet itself rotated 366 1/4 times (the Earth rotates in the same direction around its axis as it does around the Sun: seen from the northern sky, counter-clockwise).

Midnight, in sidereal time, is when the First Point of Aries crosses the upper meridian.

A mean sidereal day is reckoned, not from the actual transit, but from the transit of the mean vernal equinox (see: mean sun).

A tropical year (also known as a solar year) is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere) relative to the equinoxes and solstices. The precise length of time depends on which point of the ecliptic one chooses: starting from the (northern) vernal equinox, one of the four cardinal points along the ecliptic, yields the vernal equinox year; averaging over all starting points on the ecliptic yields the mean tropical year.

On Earth, humans notice the progress of the tropical year from the slow motion of the Sun from south to north and back; the word "tropical" is derived from the Greek tropos meaning "turn". The tropics of Cancer and Capricorn mark the extreme north and south latitudes where the Sun can appear directly overhead. The position of the Sun can be measured by the variation from day to day of the length of the shadow at noon of a gnomon (a vertical pillar or stick). This is the most "natural" way of measuring the year in the sense that the variations of insolation drive the seasons.

Because the vernal equinox moves back along the ecliptic due to precession, a tropical year is shorter than a sidereal year (in 2000, the difference was 20.409 minutes; it was 20.400 min in 1900).

Answer 4

you mean what and why is the (Light year) right?...because, i we calculate on Km per hour is allways giving us big big big number.... we don't want wast time to write this number to describe the speed in space....just like you stand from ground and turn on the torch, people from far far away on 100km on the moutain can see the light of your torch in a second...that how fast the light travel in straight line in hundreds kms...in space , the distance so long longsss.....rather we say from this planet to other planet in many millionsssssss km away, we just say 1 LIGHT YEAR away. Simple is that.

Answer 5

You mean tropical or sidereal, and the answer is tropical.