[Avodah] Gezeros in the BHMK

[Zev Sero]

Simon Montagu wrote:
> Zev Sero wrote:
>> Bimchilas kevodo, that makes no sense.  The half-hour was to see the
>> sun (or its shadow) move noticeably from its noon position.  The sun
>> moves at exactly the same rate regardless of the day's length.  If on
>> 21-Jun the shadow reaches a certain point on the BHMK wall at exactly
>> 30 minutes past noon, then on 21-Dec it will also reach that point at
>> exactly 30 minutes past noon, and not a moment earlier.

> I'm not sure that the seifa follows from the reisha. Isn't the "equation 
> of time" also a factor here?

No.  The equation of time tells you when noon is.  We're talking about
half an hour *after* that time.  If you're determining noon directly
from the sun, then you don't need to know about the equation of time.

(Except according to RMF, who holds that the halachic chatzot is the
average noon, not the noon of that particular day, i.e. (before allowing
for standard time) chatzot is at exactly 12:00 every day. According to
him you can't use the sun, or if you do then you need the equation of
time to tell you how far the real sun is from the "average" sun.)