Daughter needs to prove Earth's axis tilt with stars

beckorite · Feb 23, 2006

We r new and have done some star observations (including Polaris). We want to take my survey equipment to prove Earth's axis tilt for her science fair. I have the capability to shot the edges of the sun with a solar filter and do have GPS equipment as well. We can prove the lattitude with polaris or GPS. Earths rotation will probably have 2 be averaged at different times taken with international time? Old time astronomers did it with there equipment im sure. R we on the right tract?

harmonicaman · Feb 23, 2006

I think you would have to measure the Sun's angle at specific times of the day for one year. This page has some data.

beckorite · Feb 23, 2006

Hey, I really appreciate the information. I think that by shooting the top or bottom of the sun several times during the day, this will allow us to calculate the Sun's declination for that day (with international time and my surveyor equipment)! Ive used old solar ephemeris tables before in doing solar shots. Once we prove the alltitude data of this chart, we can then use the charts with some graphical autocad drawings to prove our point. Afterall, everyone knows and takes for granted our 4 seasons. Few know why they really occur. Thanks Beck

Saiph · Feb 23, 2006

you can actually find the sun's declination with a stick and it's shadow. What needs to be done: You merely mark/record the position of the of the shadow cast by an upright stick, when it is at it's shortest (i.e. solar noon, which will most likely not mesh with the clock!). This will occur when the sun is due south (well, up, and due south <img src="/images/icons/smile.gif" /> ). You need only mark the end/top of the shadow by the way. To find the altitude (in degrees above the horizon) of the sun, just do a little math (you know the height of the stick, length of the shadow, and the 90 degree angle). This alone, done over a few weeks, will show the sun getting higher (this time of year) in the sky. Daily measurements help, but aren't necessary (a couple times a week is just fine). do it for the year, and you'll get an analema: To convert from altitude to declination: here's a general (well, not so general) diagram I dug up from a prof I know: physics.unl.edu/~ducharme/ASTR103/EXAMPLES/Wks11.pdf basically, the North Celesital pole (polaris) makes an angle = to your latitude. The celestial equator is 90 degrees from that. The CE has a declination of 0 degrees. Put the sun on the semi-circle the number of degrees away from the southern horizon you found. Measure/calculate the angle between the CE and the Sun. In brief, thats 90-lat = height of CE. Find the difference between that and the star/sun's position for declination. So if sun is at an altitude of 70 degrees (near it's summer high point) from lincoln, my hometown, thats 90-40 (lincolns lat) = 50 altitude of CE. 70-50=20. Sun's at declination 20. Or, at winter low of ~30, get 30-50= -20 or negative 20 degrees declination. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Feb 23, 2006

shuttle_guy: That'll show you precession...which is small on a yearly basis, because everynight, the earth's spin axis will point at basically the same point. If you want to show it's tilted with respect to the solar system: Do as above...and point out why polaris is special (i.e. do the time elapsed stellar arcs shuttle guy mentions). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Feb 23, 2006

Well...you could take observations of planets moving through the sky, show how those vary in distance from the celestial equator. Use the stars as reference points. That could do it. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

harmonicaman · Feb 23, 2006

Since the Earth's axis is tilted only as it relates to the Sun; I don't think there's any way to prove it is tilted without also referring to the position of the Sun. Prooving it by measuring the angles of the other planets would work too, I think; but that sounds very complicated!

Saiph · Feb 23, 2006

you could show it's tilted with respect to the galactic equator...but that's only noting that the milky way isn't parallel to the ecliptic, or the CE. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

dragon04 · Feb 23, 2006

One simple way to do it would be to take a series of pictures at the same time of every day of the same point on your local horizon.. Or every 3 days or 5 days, etc. Let's say that your local sunset it as 5:56pm tomorrow. Take a 35mm camera, take it off of auto, and set your f/stop at a setting of your choice. Then for 24 days, (assuming a 24 exposure roll of film) take a picture at the same exact time every day. If you are headed towards spring in your hemisphere, the pictures will brighten over time. And the converse for the opposite hemisphere. <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

harmonicaman · Feb 23, 2006

Here's a thought, make a big pin hole camera and take observations of sun during sunspot activity. The track of sunspots across the Sun's equator will be at an angle of 90o to the Sun's axis, which will be 23.45o from the Earth's axis on both Equinox's (and 0o on the solstices).

Saiph · Feb 23, 2006

The position of the stars in the sky is almost completely constant throughout the year. The only thing that changes is the time of day they're up (i.e. wether they have to compete with the sun or not). Basically, any given star traces the exact same path, every day, all year long. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

dragon04 · Feb 24, 2006

I understand what you mean, S_G. I'm assuming one could use our host star as a reference. It's a star after all. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

beckorite · Feb 24, 2006

Very good discussions! Here is what I thought would be a way 2 accomplish the task. 1. Determine LAT?Long (GPS Receivers-Surveyor grade by the way it uses the Russian satelites also in determining the position, or by observing Polaris with my theodlite) of 2 pts for my observations and control pts. 2. Then use my surveyor's program to perform a solar observation (Using a solar filter)to determine the astronomical azimuth between the two control pts. This way I have a backsight reference pt. 3. Then by sighting the top and leading edge of the Sun, I can determine the alltitude of the sun by using international time. By recording several shots in the morning and evening on several days, I can then prove the Solar Ephemeis Tables for those particular days. These tables has the exact alltitude of the sun (which must be interpertated for the exact hr) and has the diameter of the sun. 4. Once these Solar tables are proven, then we can use them as our guide to look up the varies equinoxes and Solstices for earth. I think proving these tables, should allow me to use their data. Thereby finding Dec 21, March 20, Jan 3, and Sep 22 are the dates that the earth's 23.45* tilt and the position of the earth in its orbit around the sun is the reason for the seasons. Perfect page http://solardat.uoregon.edu/SolarRadiationBasics.html

Saiph · Feb 24, 2006

Tiger: Stars always rise to the same maximum height every day. What changes is when the star rises, but this is caused by the earth's revolution around the sun, not the axial tilt. So a star on the celestial equator, will always be there, will always rise to the same height, but not at the same time every day. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

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