International Astronomical Union (IAU) average a =149597871 km. Least distance, perihelion = 147098074 km and maximum, aphelion = 152097701 km

If ##theta## is Earth’s heliocentric longitude at any instant, the

distance r at that instant can be approximated from

##(1.495975 X 10^8)/r=1+0.0167086 cos theta##, where

##theta## is the heliocentric longitude of ‘s center, with

##theta = 90^o## at vernal equinox ( about March 20).

At vernal equinox, r = semi latus rectumm l = ##1.495975 X 10^8 km##.

0.0167086 is the eccentricity e of the Earth’s orbit and this

approximation is differing in different sources. In brief, all these data

used.might not be the same, uniformly, in all the sources, when we

look for more significant digits.

There are limitations, like 0.001 sec, in angular measurements. This

is the reason for the variations. in lower significant digits (lsd)..

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