[Tron]

Hey Guys,

I'm running an experiment to see if the Sun changes its apparent diameter from Sunrise to Noon...

This morning in NY at 8:00AM i measured the sun as 3/8th's of an inch accross (a little less then a 1/2 inch).  I'll check again around solar noon. 

UPDATE:  I measured the width of the sun again at 11:40AM.  It appeard to be between 1/8 and 1/4th of an inch long (a little less then a 1/4 inch)   

I'll double check the results later, but right now the sun seems to appear smaller around noon.

[markjo]

How are you measuring the diameter of the sun?  Are you accounting for glare?  Are you protecting your eyes the the sun's intense rays?

[Tron]

I used a pencil compass with two sharp ends...  I think I removed enough glare for accurate measurements...  I used the trees in the morning and the trees/sunglasses in the afternoon. 

[DuncanDoenitz]

Item 1:  Before we go any further; for Christ's sake be careful with your eyesight; you won't get a second chance.  Research how to safely look at the sun.

Now lets critique your science.  "3/8 inch", "between 1/8 and 1/4 inch".  What?  I thought even FE took it to be several miles across.  I assume you are measuring the apparent diameter at some distance from your eyes.  What distance?  How have you measured the range of your compass points from your eye?  Are you using the same distance for every observation? 

Sunglasses are totally inadequate for this task (see Item 1).  If you are looking through trees you are partially obscuring the thing you are attempting to measure.  Unless you are looking through something like welder's goggles you are only measuring the glare, not the sun. 

Finally, read Item 1 again. 

[Pete Svarrior]

Regardless of any other disagreements, I'd like to strongly echo our RE friends' suggestion - please be very careful when looking at the Sun. It can, and will, damage your eyesight if you don't use appropriate protection. Trees and sunglasses are not enough if you're looking straight at it and trying to take measurements.

[Tron]

I think the world spins and the sun is stationary.  The reason the sun doesn't light up the whole world is because of the way the Earth tilts towards the sun and how the light bends around the atmosphere....  This creates areas of light and areas of dark on Earth.  That's why we can use time zones but it's generally 12pm when the sun is directy over a  location...

 Time zones I guess are important so everyone starts and ends a calendar day at the same time...  I think 12am in Greenwich UK is when a new day officially starts followed by the countries approaching 12am midnight ..

[ichoosereality]

As other's have said, be very very careful of your eyes here.

I suggest using a pin hole device for such an experiment.  Get yourself a mailing tube in the 2-3 feet long range.  Cover one end with aluminum foil securing it around the tube with tape.  This will be the end in which you poke a tiny hole in the center with a pin.  Do the same on the other end but with paper that is not so heavy that the light will not shine through to some extent.  Wax paper will work but you can not draw on it easily so just light (cheap) white paper is likely good.  Then when you have it aligned with the sun you will see a small dot on the paper (again do not put your eyes in direct line here even with the paper on).  You can then look at it from the side and either measure directly or carefully trace around the dot and measure later.  Positioning the tube and holding it steady will be the hard part.  Attaching it to a camera tripod (even with just duct tape) might work.  Also the image does not have to be centered on the paper, so you can have them move across the paper as the day goes on and then they will be easy to compare.  Not having them centered will make a tiny difference in size since the length is different but only very very slightly.

[Tumeni]

I think the world spins and the sun is stationary.  The reason the sun doesn't light up the whole world is because of the way the Earth tilts towards the sun and how the light bends around the atmosphere....  This creates areas of light and areas of dark on Earth.  That's why we can use time zones but it's generally 12pm when the sun is directy over a  location...

 Time zones I guess are important so everyone starts and ends a calendar day at the same time...  I think 12am in Greenwich UK is when a new day officially starts followed by the countries approaching 12am midnight ..

WHY do you "think" this ...?

[drand48]

Better yet, try measuring the full moon.  If you do it carefully, you'll get the same results regardless of where it is in the sky.  No fear of eye damage.

My results, using a micrometer at arms length, were that the moon has the same diameter at moonrise as it has when at culmination (as high in the sky as it will be.)  About 11 mm, IIRC.

It was important to make sure that the distance from my eye to the micrometer was constant.  When the moon was on the horizon, I faced it and held the micrometer at arm's length, vertically.  When it was at culmination, I faced the horizon directly under the moon just as before, and then bent backwards so that my head-shoulders-arms-hand angles stayed the same.  Fortunately I don't live in the tropics where this would have been difficult (since the moon would be much higher in the sky at culmination.)

[Tron]

Okay, I measured the Full Moon today at 8pm and 1:15am (Culmination)...

At 8pm it measured .5mm  (twice measured)
At 1:15am it measured .3mm and .35mm

I held a compass needle arm's length in both instances and wore sunglasses to reduce glare.

At Culmination without sunglasses the moon measured slightly bigger at 5mm,4mm,.35,.4. I didn't measure it at 8pm w/o sunglasses but I assume it would measure slightly bigger as well.

[VerraNox]

Thats impossible. The distance from earth to the moon cant change so drastically in such a short period of time. It could be that you messed up. Next time try take measurments with your arm fully extended in both cases. Lets see if the  results will change.

[Magicalus]

Could I suggest using a stationary measuring implement, instead of one you hold? The shaking inevitably produced from holding something at arms length could cause inaccuracies in the results. Maybe something like a ruler on a tripod, where you line your eye up with it and the moon.