Need axial tilt info of earth daily


by axialhelp
Tags: axial, daily, earth, info, tilt
axialhelp
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#1
May25-13, 07:14 AM
P: 2
so i wanted to know for my own GK about earths daily axial tilt.So far i have found only axial tilt on solstice and equinox.
there is one way but it is cumbersome and that is to manually find it
https://www.youtube.com/watch?v=cuGZpl0lkXU
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Bandersnatch
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#2
May25-13, 11:32 AM
P: 550
Hello, axialhelp. Welcome to PF.

Axial tilt of the Earth is always the same. There's some variation due to nutation and long term(thousands of years) perturbations, but in the time scale of human life or without the need for extreme precision, the angle of tilt remains 23,4 at all times.
This is the angle at which the Earth's axis is tilted away from the line perpendicular to the plane of its orbit.

What does change during the year, is the relative position of the Sun with respect to the direction the axis is pointing.

This causes the angle between the axis and the plane perpendicular to the direction to the Sun(the plane that bisects the Earth in two halves: the illuminated one and the one in shadow, or, day and night halves) to change from the maximum of 23,4 at Summer solstice, through 0 at equinoxes, to -23,4 at Winter solstice.

To find this angle at any given day of the year empirically, you need to do exactly what that BBC video told you to do.
If it's any time between the solstices, you'll get the angle between -23,4<α<23,4.
They even got such a result themselves, due to making measurements a few days before the summer solstice, as the lady tells you at the end of the video.

You could use sun path charts, like this one(http://solardat.uoregon.edu/PolarSunChartProgram.html) to get the data you need for the calculations without leaving your room.

Alternatively, to a good approximation, you can just use this equation to get the angle you want:
[itex]α=23.4\sin({\frac{2\pi}{365}x})[/itex] where x is the day of the year counting from the spring equinox. When calculating remember that the value in the sine function is in radians, but the end result is in degrees.
axialhelp
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#3
May26-13, 05:04 AM
P: 2
Thanks but i am unable to understand it or compute it.CAn you compute the axial tilt of earth every 15 days starting from dec 21?. is there any website which has the axial tilt for each day? .
Anyways my question was i wanted to find out the effects on earth if the axial tilt would be halved by 50%. How would the season be ?

http://io9.com/5829438/earth-doesnt-need-the-moon

russ_watters
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#4
May26-13, 11:04 AM
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P: 21,997

Need axial tilt info of earth daily


Again: earth's axial tilt is constant.
jim mcnamara
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#5
May27-13, 06:02 AM
Sci Advisor
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P: 1,354
Are you trying to do some kind of astrography or sun angle project? In other words, what are you trying to figure out, in plain words? The answer is not change in axial tilt, it is change in ______ relative to: ______ (you fill in the blanks).

Your attached link shows the sun's angle versus the Zenith -> to get the axial tilt of the earth: 23.4 deg -- On the summer Solstice @noon. The axial tilt does not change (from a normal human perspective anyway) all through the year. The angle of the sun at astronomical noon changes, but if you correct for that you get the same answer over and over.
Bandersnatch
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#6
May27-13, 09:53 AM
P: 550
Quote Quote by axialhelp View Post
Thanks but i am unable to understand it or compute it.CAn you compute the axial tilt of earth every 15 days starting from dec 21?. is there any website which has the axial tilt for each day?
Spreadsheets are your friend.
http://speedy.sh/3kARu/sunposition.ods
(it's an Open Office file)

There's two spreadsheets there.

The first one calculates the deviation from the position of the Sun at noon during equinoxes(in degrees).
At equinoxes, the Sun's elevation is equal to 90 minus your lattitude. The value calculated is the angular distance that the Sun appears to move up and down from that point over the year.

The second one calculates the actual position of the Sun at noon as measured from above the Southern horizon. It's simply 90 minus your lattitude plus the deviation value.

I'm guessing these are the values you are looking for.

You can enter new values into the cyan-coloured cells. The first one is the axial tilt, which, we cannot stress this more, does not change.
The second one is the lattitude from which you're observing the Sun.

It uses the same equation as provided in post #2, which assumes circular orbit. This is not really the case with Earth, so keep in mind that actual values will differ slightly.
There's also the case of refraction, that causes the Sun to appear higher above the horizon than it really is. (http://en.wikipedia.org/wiki/Atmospheric_refraction) This effect is obviously not included, so the values close to the horizon will differ some more in reality.

Anyways my question was i wanted to find out the effects on earth if the axial tilt would be halved by 50%. How would the season be ?
You should be able to see that the position of the Sun would deviate less from the equinox position, which means that Summer and Winter would be less extreme and more like Spring or Autumn.


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