why does the lenght of days and nights on earth varies at different times of the year?
84070
As the earth journeys arond the earth on its orbit, sometimes the northern hemisphere is tilted more towards the sun, and sometimes the southern hemisphere is tilted more towards the sun. \n\nIf your hemisphere is tilted more towards the sun, then you will have longer days and shorter nights. If your hemisphere is tilted away from the sun, then you will have shorter days and longer nights. \n\nThe tilting is caused because the earth's rotational axis is not orthogonal to the plane of its orbit, called the ecliptic.
828997
I believe you are referring to the changes in the seasons.  Because the rotational axis of the earth is tilted a bit more than 23 degrees away from it's orbital plane the earth gets a bit more in the way of the sun (so to speak) as winter approaches so sunrise is a bit later each day, and sunset a bit earlier.  After the winter solstice less and less of the earth is in the way, so sunrise starts a bit earlier each day, and sunset a bit later, until the summer solstice.  Interestingly dusk is longer in the winter because the sun rises and sets at more of an angle to the horizon.  For the same reason, in the tropics dusk is shorter because the sun rises and sets more nearly vertical.  In the more northern part of the northern hemisphere and the more southern part of the southern hemisphere dusk may last all night long in the summer (culminating in the "midnight sun" north of the arctic or south of the antarctic circles).  In addition, due to the refraction of the atmosphere we see the sun earlier than actual sunrise and later than actual sunset (the atmosphere acts as sort of a lens).
259299
only the exact spot at the north pole and south pole have one day per year. Alaska is not at either of these places.\n\nHowever, at the poles, the reason for the one day per year effect is that the earths rotation at these two places does not cause any crossing of the earths terminator (region darkness starts to envelop the earth) at any time of the year. \n\nAreas inside the artic and antartic circles do have extended days (weeks to months depending on how close to the pole), but only the exact spot at the poles have 6 month light/dark phases.
606605
It's not different months, it's times of the months. This is because the of the moon's position in relation to us. The moon always faces us with the same side but that is not always the lit side. When it is a full moon, the sun light is reflecting off of "our" side of the moon. In a new moon, it is reflecting off of the other side.
15804
You have the dates wrong, and the dates do shift a bit.  The vernal equinox is usually March 20 but sometimes March 19.  The autumnal equinox is usually September 22 but sometimes September 23.  Theay are always half a solar year apart.  The shift has to do with the fact that the solar year is approximately 365-1/4 days long.  It's the same reason we have leap year.  I hope this answer helps!
16493
Actually, since a full moon happens about once every 28 days, in a 365 day callender year, it can happen anywhere from 12 to 14 times.  However, neither of those numbers are precise, since the rotations don't divide evenly into 24 hour days.  The real number of the period of the moon's rotation into that of the earth's is something like 12.95
470281
The History of Analog Clocks (SEE FIRST LINK BELOW) provides an explanation of the origin of the 24-hour day. The system dates back 4,000 years, to ancient Egypt and Babylon. \n\nEgyptian astronomers divided the night hours into 12 distinct sets of star patterns, which emerged over the horizon at roughly hour-long intervals. They divided the day into 12 hours to match, and because they lived near the equator, the days and nights were of roughly equal length throughout the year. \n\nThroughout the rest of the world, the 12 "hours" of the day and night were flexible depending upon the season. It wasn't until the 13th century A.D. that an Arab scientist named Abul-Hassan suggested the idea of clearly defined hours. \n\nIt's also worth noting that the number 12 is special in many cultures. For example, Egyptians counted in base 12. Dividing the day into two sets of 12 was a simple and elegant way of condensing the annual calendar into a day. \n\n*Repost*
26830
The Earth is closest to the Sun on about 4 January of each year... Winter in the Northern Hemisphere\n\nMistWing SilverTail
747885
The night sky will appear differently to you in different years, at different times of the year, and different times of the night.\n\nThe stars appear to move across the sky each night, just as the sun does during the day, rising in the east and setting in the west.\n\nThe planets move about the sky along a path called the ecliptic, and are seen in different positions against the background of stars. Planets will be shown only on starmaps that are showing "current" conditions.\n\nIn addition, from month to month you will see a different part of the night sky, as the earth moves around the sun. The stars you see in the night sky in November are hidden from view by the sun in May.\n\nAnd of course, over the eons, the "fixed" stars are changing their positions in the sky.
710469
The variations in the passing of time can only result from gravitational effects or relativistic effects. \n\nFor relativistic effects to be aparent, you have to be travelling at a speed comparable to the speed of light. Even then, there must be different velocities involved. Therefore night/day should not make a difference, unless he is referring to the fact that you are moving around in the day (thus, relatively time passes slower for you with respect to your surroundings) and stationary in the night. However, this does not make a noticable difference at all!\n\nAs for gravity, it is not something I know very well, and don't think it is really easy to explain, but it might have something to do with being farther away from the sun (by a length of earth's diameter) during the night. Again, this should not affect the passing of time almost at all.\n\nI suppose he really was trying to make a joke of some kind, maybe based on the fact that people go to sleep after much later than nightfall and wake up early with the first lights. Also, the twilight times are usually considered day rather than night.\n\nOR: He might be referring to the movement of the stars in the night sky and the movement of the sun during daytime.\n\nNevertheless, I think it's a pretty weird question, please message me if you learn the real answer.
1080809
It isn't. \n\nBeing closer to the equator the phillipines have a more constant day length, which means that summer days and winter days are more or less the same length.\n\nIn contrast the mainland US sits at fairly high latitudes and the day lengths vary tremendously betwen winter and summer. While summer days in the US are longer than the in Phillipines the winter days are far, far shorter.\n\nIt all averages out and all parts of the Earth get the same number of hours of daylight each year.
1218
nothing to do with daylight savings. Daylight savings is a human invention, not a natural phenomenon.\n\n...because leap seconds are not being added to compensate for the Earth's rotation slowing down.\n\nThe amount of time it takes for the earth to revolve around the sun is 365.2425 days.\n\nEven that is an approximation, the decimal digits can keep going on.\n\nSo initially, the calendar was divided evenly in 365 days. But about every 4 years, you'd be off 1 day. A century later, you've drifted off by a whole month!\n\nSo, leap years came into effect. Febuary has another day every 4 years. \n\nBut now you've approximated a year to 365.25 days, when in reality, its 365.2425 days.\n\nEvery century, you'll be off 1 day.\n\nSo that's where the next rule comes into play: "If the year is divisible by 4, but not by 100, its a leap year."\n\nNow we've approximated it to 365.2425, but because its always going to be an approximation, our calendar days are always slipping. All because the earth doesn't take exactly 365 days to go around the sun.\n\nThis is why leap seconds are added, and not to account for the slowdown of the earth's rotation.\n\nAs to why days are divided in exactly 24 hours, I'm not sure. But I would think the time difference is WAY less than 20 minutes, or we'd notice that soon enough, its dark at noon! :)  Time was divided a long time ago, and a simple system was sought for keeping track of it, so the minuts/hour/year thing is a nice division thats easy to do math with. The lost time, if its accounted for by leap years and such, could be easier to manage.\n\nFirst, I never said the earth is not slowing down. I said its not why leap seconds exist. And ok, I can entertain my explanation may be wrong, but that's no reason for your condescending tone, Jolly Roger. But look, your link brings me to a christian science evanglism site, where is the evidence that my answer is incorrect? \n\nYou haven't bothered to explain his original question. If leapseconds account for the slowdown of the earth's rotation, why are there leap seconds and not leap milliseconds?\n\nIf you want to append to your answer, at least try to do so while respecting the other users on this site, and not insult their intelligence.\n\nThis has piqued my curiosity, if there's anyone out there that has a source that says my explanation is incorrect, I mean an actual science website, you know, one that steers clear of religion, please let me know.
846393
Actually, it's "equinox" that means equal night.\n\nOn the equator, the days and nights are always 12 hours long (not exactly, the width of the sun's disk plus the effects of atmospheric refraction make the days a few minutes longer than the nights). The tilt of the earth's axis affects the path the sun takes across the sky, but not the length of the day.\n\nOn the equinoxes, and at no other time, the length of the day and night is 12 hours the whole world over (except right at the poles), because the plane containing the tilt of the earth's axis is at right angles to the direction between the earth and the sun - that is, the axis is not pointing at all toward or away from the sun, and the poles are equidistant from the sun.
950609
The ancients – I don’t know how far back – noticed that life and the seasons repeated itself on a 365 day cycle.  The stars came back to the same position, the rivers would flood on this schedule.  This is why a year was set at 365 days.
281596
Yes it would be the same.\n\nDaylight saving time is used between summer and winter and not where they exist.\n\nSince the durations of day are very different in Summer and winter, it is better to have long working days in summer.\n\nThis is the reason why some countries don't follow it. Those at equator (similar suntimes in winter and summer) don;t follow and those away from equator(different suntimes in winter and summer) follow daylight saving time.
169211
In the northern Hemisphere the days are longer during the summer months and shorter in the winter months.  The opposite is true in the Southern Hemisphere.  To get exactly length of the day I think you would need a computer program.  The calculation seems a bit complicated.
137312
If the earth does not rotate on it's axis, then the only way to experience night and day would be the sun's position (as you see it) changing as earth orbits it.\n\nIt takes one full orbit to create one day/night cycle.  So the anwer to your question is "Exactly one year" for an observer who stays in one place.\n\nIf you move around on the earth as it orbits, you can make the "day" as long or as short as you like.  \n\nFor example, suppose that you traveled around the earth at a rate of one circut per year.\n\n- If you moved in the opposite direction as the sun, you would see two "days" in a year.  One "day" was caused by the orbit of the earth around the sun, the other "day" was caused by your traveling around the earth\n\n- If you moved in the same direction as the sun, the sun's apparent position would never change (you would keep up with the sun and the "day" would last forever).