Many changes occur because sometimes the shadow is . . .

long -- in the winter
short -- in the summer
in-between-ish - in the spring and fall

noon --- when the sun is on your meridian -- due south; shadows point north

Shadows can be measured at any time of day, but noon data invites more complete analysis.

Yipes -- at noon in many places in the Southern Hemisphere -- shadows point NORTH.

standard time --- is based on the sun's position relative to any meridian that is evenly divisible by 15: thus, 75 degrees - 90 degree - 105 degree - 120 degree are time zone meridians in the 48 states.

when the sun is directly south of E. St. Louis ( 90 degrees ), people in the Central Time Zone "have noon." However, at EIU the sun has already been on the meridian, while in western Missouri it has not.

By agreement, everyone pretends it is noon --- and goes to lunch.

a difference of 1 degree Longitude is equal to four minutes of clock time.

EIU is 88 degrees W. Longitude -- 2 degrees east of the "time meridian" so we get the sun 8 minutes earlier than "wrist watch noon."

We expect a sun dial to show noon at 11:52. This is called a "longitude correction"

solar correction

even when the longitude correction in mind, your sun dial will seldom register noon at the time you expect: 11:52.

That is because the sun runs ...

fast --- meaning it crosses your meridian before 11:52 -- and shadows point to the northeast because the sun is already in the southwest.

slow --- the sun crosses your meridian after 11:52 and shadows points northwest because the sun is still in the southeast.

sun fast = apr 15 to jun 14 --- 38 days --- max = +3m 45s on may 14

sun slow = jun 14 to sep 1 --- 77 days -- max = -6m 26s on jly 27

sun fast = sep 1 to dec 25 --- 113 days --- max = +16m 24s on nov 4

sun slow = dec 25 to apr 15 --- 109 days --- max = -14m 18s on feb. 11

on time = apr 15th and jun 14th and sep 1st and dec 25th --- noon shadows on time zone meridians point north on these days

# check a Farmer's Almanac for tiny changes from year to year

remember, the sun doesn't move. These shadow changes are the result of earth's spin ( rotation ) and orbit ( revolution ).