# Hatzos before 1pm during Daylight Savings Time

So it just happened, that hatzos came out before 1pm. I have a hard time understanding how is that even possible, and here is my logic. Can someone pop my bubble so I can see where I go wrong?

1. Daylight savings is not changing anything that has to do with Shaa Zmanit, it just adding 1 to the standard numbers.

So assuming at the two days in the season when Shaa Zmanit is exactly 1 hr, one is in DST (Daylight Savings Time) and one is in ST (Standard Time), one hatzos would be at 1pm and the other at noon.

Now since Shaa Zmanit usually is MORE than 60 min, during the summer when DST is in effect, hatzos should be at least somewhat after 1pm.

But, it's not. What's wrong with what I am saying. I don't get it, and it's killing me :)

• Do you assume sunrise is fixed at 6am? Jul 18, 2021 at 17:34

Chatzos in the way that you calculate would be at solar noon (along the meridian) for the location that you are observing. Consider the meridian (the line along the longitude) at clock noon in the middle of the time zone. Thus, any location east of the center of the time zone would have the meridian before noon clock time. For example, Yerushalayim is approximately 20 minutes east of the center of its time zone. Thus, when chatzos is at noon in the center of the time zone, it would be at 11:40 AM clock time in Yerushalayim. Perhaps this is the situation that you are observing.

As an example, solar noon today in Jerusalem was 12:45 (Daylight Savings Time) which would be 11:45 AM standard time. Calculating chatzos shows a 14 hour day with sunrise at 5:46 AM which verifies the meridian.

What is Solar Noon

When Is Solar Noon?

In most places on Earth, solar noon does not happen at 12 o'clock. The Earth's rotation slowly shifts the meridian experiencing solar noon from east to west. In other words, solar noon happens a little earlier in locations just east of you and a little later in locations west of you.

Where's Sun right now?

Since our clocks are set according to time zones, civil time changes abruptly as you move from one time zone to another, usually in 1-hour increments. While this undeniably makes life easier for us, it does not reflect the even movement of the Earth's rotation and the gradual geographical progression of local solar time.

This means that clocks in the eastern part of each time zone show an earlier time at solar noon than clocks near its western border. Even if time zones were used the way they were once envisioned—where local time is based on the solar time in the zone's center, with the time zone extending 7.5 degrees of longitude to the west and to the east of the center line—solar noon would occur at 11:30 (11:30 am) at the eastern time zone border and at 12:30 (12:30 pm) at the western border.

• This is only true on the equinoxes. Even east of the center of a timezone can sometimes have noon after noon at other times of year Jul 19, 2021 at 1:43
• @DoubleAA Yes but the definition of solar noon is the moment the sun hits the meridian. The clock noon is basically close to solar noon at the center of the time zone. The farther east or west within a time zone the more the difference shows up. Jul 19, 2021 at 17:55
• "The clock noon is basically close to solar noon at the center of the time zone." What do you mean by basically? There are two factors at play here (location and season) and you are acting as if there is only one. Jul 19, 2021 at 18:08
• @DoubleAA The official definition of solar noon is the moment of meridian. That is what I am using to explain chatzos. Thus, chatzos is always solar noon at the exact center of the time zone. While clock time might differ, it only differs by a small amount. London for example is 5 miles off the Prime Meridian (7'32.66E) which has noon at 1:06 PM today. timeanddate.com/sun/uk/london The difference by season only affects clock time not solar time. Jul 19, 2021 at 18:30
• "The official definition of solar noon is the moment of meridian." This can't be true since I don't even think "the moment of meridian" is an English phrase. A meridian is a line not an event. Chatzos is always solar noon at any point in the time zone, not just near the middle. All we're talking about is when chatzos is not at 1200 clock time and you haven't discussed the equation of time Jul 19, 2021 at 18:37

From

https://dinonline.org/2012/03/13/rav-moshes-chatzos-2/

According to Rav Moshe Feinstein, ZT”L chatzot is always the same time ,11:56. Does this time change either forward or backward when the clock changes (winter or summer)? And is this time always the same in different countries?