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## Wednesday, November 15, 2017

### The simplest method to measure the geocentric lunar distance: a case of citizen science

Cool paper on measuring the distance to the moon by comparing the angular size:

The essence of this methodology is that the distance to the Moon changes over the course of the 6 hours between when the moon is near the horizon and near zenith sufficiently for us to measure this change in the angular size of the Moon.

From Figure 1 in the paper we're discussing the following geometry.  Please note that it is the observer that is suggested to be moving with the rotation of the Earth and not the Moon.

For ideal conditions (an observer near the Equator at the Equinox) the change in angular size would be expected to be simply:

Δϕ/ϕ ~ Rₑ/D ~ 1/60 ~ 1.7%

Therefore, if the Earth radius is ~3959 miles (6371 km) and rotating we would expect to observe a 1.7% change in the size of the Moon over this span.

The paper gives the more exact formula that also takes into account the observer latitude and the lunar orbital conditions, but would we expect this variation to be repeatable for all observers, at all times.

We do in fact see exactly this variation which is a variation that Flat Earthers are forced to appeal to magic to explain while the Heliocentric/Globe models explain it effortlessly.

It's a neat paper and I recommend giving it a shot if you have a decent camera and lens.