Sunday, June 04, 2017

Sunday science

Rhonda and I did some Sunday science.

We discussed Moon phases and the confusing terminology and concepts. Like, why is it called First Quarter when the Moon is half-lit. I clarified that the phase refers to the orbital position, which I found very curious, as it requires a big leap. The observer must take up a vantage off the Earth, in outer space, viewing the Earth-Moon system in three dimensions. I think this is challenging for some.

Got out my Shasta marbles for the Earth, Moon, and Mars. Grabbed the LED flashlight from the kitchen. Demo time! I think it helped rho a lot to see it this way.

We talked about prograde motion which most planets and moons follow. But some go the other way, retrograde. [ed: This is incorrect use of the terms. Better to say counterclockwise and clockwise.]

We simulated lunar and solar eclipses (er, occultations).

Lodged my complaint about "Last Quarter." To me, the last of something means final. To me, Last Quarter should refer to 4 of 4, the New Moon phase. I would prefer that only Third Quarter be used to describe position 3 of 4 in the lunar orbit.

We talked about tidal locking. The Moon of course keeps the same face toward the Earth. She asked if it only applied to moons. I shared that Mercury is gravitational locked to the Sun.

In Stellarium, I showed the Earth-Moon system from the Sun and sped up time. We watched the Moon slowly orbit around the planet while we could make out the Earth rotating briskly.

Then I showed the Earth from the Moon surface and sped up time. While the rapidly spinning blue planet never set, it bobbed and weaved, due to libration.

rho does not like the terms sunset and sunrise. It propagates the idea that the stars and planets are moving across the day/night sky when in fact it is due to our planet's axial rotation. These classic terms are appropriate in a geocentric system but confusing in a heliocentric model. I agreed. But what would be better terms? Ingress and egress? Dunno.


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