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I was under the impression that the longest day was June 22nd, and yet, year after year- the latest time for candle lighting takes place about a week and a half after that. Intuitively, the latest candle lighting time should coincide with the longest day. Here are some times from this year.

{18 Jun 8:14} {25 Jun 8:15} {2 Jul 8:15} {9 Jul 8:13}

Why is this?

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2 Answers 2

YDK's answer perpetuates the common misconception that it is the ellipticity of the Earth's orbit that causes the latest sunset not to fall on the longest day. But this is not true. The primary cause of the phenomenon is the obliquity of the Earth's axis, that is, the fact that the Earth is tilted with respect to its orbit around the sun. The ellipticity does contribute, but not as much, and in fact in the summer its contribution goes the other way: If the Earth were not tilted on its axis, the latest sunset would precede the longest day. (That's why the longest day and latest sunset are closer together than the shortest day and the earliest sunset---in the winter, the obliquity and eccentricity work together.)

A complete explanation can be found here: http://larry.denenberg.com/earliest-sunset.html

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This is because the sun doesn't use a timex, it has its own path which is not as "precise" as our timepieces.

The Earth doesn't go in a nice circle around the sun, it travels in an ellipse (Kepler's 1st law of Planetary Motion). When the Earth is closer to the sun (in our winter) it travels faster. When it is farther away (in our summer) it travels slower. The cause of this is gravity-similar to when you put a coin down a march of dimes wishing well at the zoo. It can be illustrated using Kepler's 2nd Law of Planetary Motion. The end result is that our watches are off from the sun's "motion".

Although the Sun's time is relatively close to the time on our watches, Kepler's laws have an halachic ramification for kidush hachodesh. Rosh Hashana 24b:-25a Two witnesses said they saw the old moon in the morning and the light of the new moon in the evening. Rabbi Yochanan ben Nuri tossed them as fabricators since the calculation was that a new moon is covered for 24 hours. Rabban Gamliel accepted them since he had a mesorah that the moon's movement fluctuates. (The amora Rabbi Yochanan brought a supporting pasuk- "Shemesh yada mevo'o"- but not the yareach).

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To put it in different terms, the days indeed start getting shorter after June 22, but the times of solar events (sunrise, noon, and sunset) as recorded by our clocks all continue to slide later for a few more days, due to the phenomenon YDK has described. There are many sites that explain this in detail; here's a random one (regarding the opposite case in the winter): curious.astro.cornell.edu/question.php?number=208 –  Dave Jul 27 '10 at 2:59
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the sun's path is FAR more precise than a Timex, just not as uniform. We can calculate the time that the sun should be in a certain place in a thousand years from now, with accuracy of better than a second. A quartz crystal would be off by more than an hour, assuming the battery still works. –  Jeremy Jul 27 '10 at 21:28
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I think you mean that the sun's "movements" are more accurate than that of a watch, but they would be less precise since they span a broader range. Unless you're talking about it's movement relative to the stars (which I'm not sure about). I was referring to its apparent movement from Earth-view. –  YDK Jul 27 '10 at 23:10
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The sun's movements are precise in and of themselves, since they follow a set of rules with exact precision - more so than any mechanical device, which will slowly deviate from its target measurement. When solar events fail to correlate with our system of timekeeping, that doesn't mean that the sun is less precise than a watch, all it means is that the precise movements of the sun are less uniform than our steady-ticking watches. –  Dave Jul 28 '10 at 4:36
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Alright! Uncle! –  YDK Jul 30 '10 at 1:54

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