Forward-double Reflection

Double Reflections - part 1 planned

This past winter, I came across some interesting geometry as I re-checked my building orientations and azimuths, in preparation for moonrise reflections: the "double-forward" case.

In this plan view of a section of downtown Edmonton, sunlight or moonlight enters from the left (west), reflects off the west face of the MNP building, zips across to the east face of Bell, reflects a second time, and exits to the east, slightly south, to me and my camera stationed at the Forest Heights scenic spot. Here is the view from the bench behind the tennis courts:

Although the diagram (Fig. 1) makes it appear that there is no change in the angle, the fact that the building faces are not parallel means there is a slight difference between the Bell azimuth, 287 and the Sun at 276. Technically, this means that in one field of view of 14 degrees wide, I can simultaneously capture the Sun and its reflection. But sometimes one cannot have all the luck, and in this case the direct view is blocked by other buildings.

When the setting Sun reached an azimuth of 275 in the spring of 2016, calculations predicted that I would see a double-forward reflection from the hill crest at the top of 98 Ave, near St Joseph's seminary. Because skyscraper windows are not perfectly flat, the diameter of the Sun is 1/2 degree, and the sky right next to the solar disk is bright, there is a leeway of a couple of days on either side to catch the reflection. Right on cue, April 1, 7:50 pm:

A short time-lapse of this 15-minute event can be seen at https://vimeo.com/161419180.

It's only a matter of time before we can catch a moonset double-reflecting. Once we've done that, we'll up the ante and look for a triple reflection, and perhaps a quad using the river's surface.