Change in Daylight Time
the earth's axis is affected by the moon's gravitational pull causing it to wobble by a couple millionths of an inch; the ocean's tides are also affected by the pull the moon.
Sunrise, sunset change due to eccentricity
A lot of this is just due to rounding. Most sunrise/sunset tables are in whole minutes, so the changes appear less regular than they are. But there is an astronomical reason for the variations in time.
If the earth's orbit were a perfect circle, we would see the same change in sunrise and sunset every day. For example, on a given day in the fall, sunrise would be 90 seconds later than the day before, and sunset would be 90 seconds earlier. But it's not a circle, it's slightly elliptical, so the speed we move around the sun changes throughout the year. This causes solar time to be a little off from clock time, and by a different amount each day. This is reflected in the analemma, the figure-8 thingy often found on globes. Also try searching on that word, and you will find a bunch of interesting stuff.
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A circular orbit for the earth would not be quite enough for the above to be true. The earth's axis is tilted by about 23.5 degrees, and this also affects the irregularity of changes in sunrise and sunset. Combining this tilt with the fact that the solstices (the points where the plane formed by the sun's center and the earth's axis is perpendicular to the plane of the ecliptic) do not occur at aphelion and perihelion as is often assumed, brings about the interesting patterns of sunrise and sunset. After the winter solstice, which happens several days prior to perihelion, sunrises continue to happen later each day for a few days, even though the total length of daylight is increasing. Studying the analemma is a good idea, and studying the Equation of Time will help also. See links.
First answer by Ghostrunner. Last edit by Emdrgreg. Contributor trust: 671 [recommend contributor]. Question popularity: 62 [recommend question]
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Answers.com > Wiki Answers > Categories > Science > Astronomy > As the season progresses the time of sunrise and sunset changes but why is the change in time unequal eg sunrise may change by 2 minutes but sunset may change by only 1 minute?
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