It's lunar new year here and people will be lighting fire crackers and launching bottle rockets off and on until dawn, so I thought I would read up on it. EarthSky.org's Moon Phases update Your new moon is January 27 or 28 is really interesting, including some photos of actual new moons by Thierry Legault, the photographer who's taking those amazing photos of the ISS passing in front of the Sun, or the Moon.
But the next item down, Lengths of lunar months in 2017, is also really interesting both technically and visually, because it has this amazing GIF of the moon's changes in appearance over one orbit, shown below. This version is much better quality than the one from Wikipedia that I've used here and here. But I am not sure where it's from or how to read about it.
The information for the Wikipedia-sourced animation is difficult for me to understand already. The period is a "Draconic Month of nodes", but is that actually the same thing as the time between successive apogees? The issue here is how to generate a smooth, cyclic GIF, since an exact simulation would be jumpy - no two orbits are the same in the real world.
Also, how is the shading calculated, what kind of shader is used (diffuse reflectivity model) for the oblique sunlight incidence?
While an actual answer would be fantastic, a link to a source of the information would be helpful as well.
Source bitmap for projection from NRL's Clementine Spacecraft:
- USGS: Global simple cylindrical projection at 10 km/pixel.
- 50 frames were created, equally spaced in time.
- Period used: 27.21222 days (Draconic month of nodes)
- Animation began and ended at Apogee to minimize "jumping" when cycles back to the start.
- New moon given an unreal 1% intensity "Ambient light" to show motion in all phases.
- View assumed from the center of the earth. (Geometrically impossible, but best demonstration of monthly libration caused by moon's motion versus the shorter daily libration that would be included from the surface of the earth.)
Animation used in EarthSky.org:
Animation from Wikipedia: