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48 votes
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How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

This is not so hard to do. All you really need is a bit of care, a few sticks and a convenient place to observe the sunrise or sunset. So note that there is a cycle of the year and you want to know ...
James K's user avatar
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25 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

It's easier than you think to notice the fraction... simply because the rounding error compounds over the years! After a good amount of years, you notice that solstices are drifting from their ...
Offirmo's user avatar
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24 votes

Is it coincidence that the earth's rotation and revolution are in the same direction?

Not a coincidence, most other planets rotate the same way. It is a consequence of how planets were formed from a disc of gas and dust that was orbiting around the sun as it formed. The sun formed ...
James K's user avatar
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24 votes
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Earth is Tilted, but in reference to What Object / relative to what?

The orbit of the Earth around the Sun defines an orbital plane. The equator of the Earth is (currently) tilted at an angle of 23.4 degrees to this orbital plane. Or to put it another way, the spin-...
ProfRob's user avatar
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18 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

The ancient Egyptians appeared to know that the year was 365.25 days. This was established by observing on what day the heliacal rising of Sirius occurred (i.e. on what day that it first becomes ...
ProfRob's user avatar
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16 votes
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Are galaxies growing, shrinking or stable?

Right now big galaxies like the Milky Way are growing by absorbing smaller galaxies - this is happening right now to the Sagittarius Dwarf and in the past to several other galaxies. Plus, there has ...
Anders Sandberg's user avatar
16 votes
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Is it coincidence that the earth's rotation and revolution are in the same direction?

I think it is coincidence, apart from that there may be anthropic arguments for the spin axis inclination (the difference between the spin and orbital axes) to be small but non-zero. i.e. A small, but ...
ProfRob's user avatar
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11 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

For the most part, they didn't. Calendars have historically been a practical device. They were used to measure times of events, such as the planting and harvesting of crops. They only needed to be ...
Cort Ammon's user avatar
7 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

There is a good article in the Britannica. It seems the Sumerians used a 360-day year, and stuck an extra month in when the seasons got too far out of whack. The present year is a leap year(sic). The ...
Simon Crase's user avatar
7 votes
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What are the effects of mass concentration along a planet's axis of rotation?

Does this mean that Mars' center of mass is slightly shifted to the south? Yes, by about 3 kilometers, and it is also shifted by about 1.5 km along the y axis in the direction of Tharsis. See Table 4 ...
Jean-Marie Prival's user avatar
6 votes
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What does the earth's (a planet's) orbit cause?

The orbit of the Earth indirectly causes the seasons. If the Earth didn't orbit, then the seasons wouldn't change*. The Earth's orbit is slightly elliptical, this means that the Earth moves closer ...
James K's user avatar
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5 votes

Is it coincidence that the earth's rotation and revolution are in the same direction?

During the giant impact stage, the thickness of a protoplanetary disk is far larger than the size of planetary embryos so collisions are equally likely to come from any direction in three-dimensions. ...
sno's user avatar
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4 votes
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Are there any bodies in the solar system whose rotation is almost tidally locked or barely tidally locked?

The answer to this question is negative, if "almost tidally locked" signifies a small but persistent deviation from an exact resonance. The anwser, however, is positive if "almost ...
Michael_1812's user avatar
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3 votes
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What should be the "poles" for irregular shaped bodies?

For such a body (if it exists) the axis of rotation would not intersect with the surface of the body, so there is no "pole" on the surface. This might cause a few issues for cartography ...
James K's user avatar
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3 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

How do you observe those Sunrises and sunsets are pretty obvious. However, in order to accurately measure the length of day versus night, you need a type of clock that's not a sundial. A water ...
dan04's user avatar
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3 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

Count the days. Many days. You cannot expect high accuracy if you measure the thickness of a single sheet of paper with a ruler. You can improve it greatly if you stack 1000 sheets, measure the total ...
Eric Duminil's user avatar
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1 vote

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

For long-term consistent time measurements there would usually be markings put on the walls of irrigation canals which would cast a sharp shadow against the opposing wall of the stone-walled canal or ...
Amrita Bithi's user avatar
1 vote

Does rotation on their axis cause winds in gaseous planets?

It is not true. What makes wind actually be wind is that it is moving relative to something else. On earth, that something else may be you, but on a gaseous planet the only "something else" ...
Mark Foskey's user avatar
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1 vote

What is meant by sun's path through zodiac

The diagram above shows the celestial sphere - an imaginary sphere with the Earth at its center (the sky all around the Earth). The equator of the Earth, projected onto the sky, therefore onto this ...
jmarina's user avatar
  • 249
1 vote

If the Earth is rotating counter clockwise, how does the sun rise from east?

I have another experiment: Take your right hand (representing the earth) facing the back of your hand, so the thumb (left) is west and the little finger (right) is east (your middle finger is north, ...
U. Windl's user avatar
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