#### Jesse3959

##### New Member

Summary: JTolan straps an accelerometer based inclinometer to his telescope, and measures the angular height of a mountain 54 miles away. He does so from two locations, one of which is 1.3 miles farther from the mountain.

He concludes that since his two readings were only 0.002 degrees different, the earth must be flat because on a curved earth, the two readings would need to have been more different - I don't remember, maybe like 0.014 degrees of difference.

But he fails to realize that perspective would also cause the mountain to appear lower on the horizon with greater observer distance.

If I did my math right, even on a flat earth, he should have read a difference of 0.007 degrees just from perspective alone. But he didn't.

He did mention in one of his comments that the device did not read a steady value but it wandered around so he had to pick an average value.

I do not know if he actually averaged, or just watched the readout then picked a number that seemed plausible to a flat earth (but forgetting about perspective.)

Or maybe my math is all wrong, but here it is:

The mountain he was sighting off of was about 54 miles away. It's about 4460 feet above sea level. Location: 34.611432,-117.289885

His nearest and farthest observer locations were:

34.624247,-118.235647 at 53.9 miles,

34.633290,-118.257257 at 55.2 miles distance.

His observer elevation at both locations was 2952 feet.

This means the mountain (on a flat earth) is 1509 feet higher than he is.

If we take the distance and the height, we get a slope of:

arctan(1509 feet / 55.2 miles) in degrees = 0.297 degrees for the far site, and

arctan(1509 feet / 53.9 miles) in degrees = 0.304 degrees for the near site.

Is my math wrong, or did his results of 0.002 difference prove that his instruments was not working, even if the earth was flat?

Unfortnately his inclinometer was not calibrated to local level - so we can't know whether the mountain was above or below eye level. He was just using the delta of the readings. On a globe earth the mountain would have been slightly below observer eye level even though it was 1509 feet higher physically. It would be neat if he used a real theodolite and showed it to be below eye level.