EQUATION OF TIME Quandary

The equation of time, which produces the solar analemma
and determines what times of year the sun is "fast"(ahead of
clock time) or slow, indicates that at 40 degrees north latitude,
the sun is, in October, 20 minutes fast.


According to Astronomical Apps on USNO, the sun is also
20 minutes fast at 40 degrees SOUTH latitude(cutting through
southern Australia).

Now instinct tells me that the equation of time should be reversed
for latitudes south of the Equator, IE: sun should be 20 minutes
slow at mid-south hemisphere latitudes.


So am I right?

On Wed, 8 Jul 2015 17:53:12 -0700 (PDT), wrote:

The equation of time, which produces the solar analemma
and determines what times of year the sun is "fast"(ahead of
clock time) or slow, indicates that at 40 degrees north latitude,
the sun is, in October, 20 minutes fast.

According to Astronomical Apps on USNO, the sun is also
20 minutes fast at 40 degrees SOUTH latitude(cutting through
southern Australia).

Now instinct tells me that the equation of time should be reversed
for latitudes south of the Equator, IE: sun should be 20 minutes
slow at mid-south hemisphere latitudes.

So am I right?

No, on both counts.

For any given longitude, the sun transits at the same time regardless
of latitude. North of, south of, or on the equator does not change
this.

Since time zones nominally span a full hour, at the eastern edge of a
time zone the sun will transit 1 hour ahead of the western edge. For
the USNO value to be meaningful, you need to use a center line
longitude. Using 0 degrees longitude (the center line for the UTC
time zone), according to the USNO, the sun is 10 minutes fast on
October 1 and 16 minutes fast on October 31. Between those dates the
value increases monotonically so it never reaches 20 minutes.

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Barry Schwarz:

Thanks for straightening me out on that.
My initial reasoning had to do with the earth's
attitude between solstices.


Pretend you are the sun, looking out at Earth. In June, the
top half(north) tilts toward you. In December, the bottom half,
(south) tilts toward you.

In between, and surrounding the equinoxes, the earth is "slanted"
to one side or the other, even when the equator is dead straight
at you. *That* is what I thought produced the equation of time.


And actually, where I live(CT) is 2.5 degrees east of our prime
meridian(75W). That equates to solar time being 6 minutes
fast, or 16 minutes at the prime +6 = solar time being 22 min
fast. Local solar noon in late October is thus 11:38AM. Roughly
twenty minutes.