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Can a mirage function vertically?

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Rob Andrews
1296505.  Wed Sep 26, 2018 2:06 pm Reply with quote

I have just had a story recounted to me of two friends holidaying in Tunisia and settling down for the afternoon. It was daylight and the moon was visible. What happens next is odd - it seems that the moon's position appears to have suddenly advanced by something in the order of 30 or 40 degrees to sit in the opposing part of the sky. Checking out a piece of astronomical software I figured this would represent about 4 to 5 hours' movement across the sky but as two witnesses were involved it is less likely that they'd dozed off in the heat.
I understand that the month was July or August and as I was not there myself I cannot verify the apparent positional change but it is such an intriguing story and my guess is that a mirage-like effect is at play; but is this a rational explanation?
Or have I been spun a glorious yarn?

1296510.  Wed Sep 26, 2018 4:10 pm Reply with quote

Is it possible that one of the sightings was of something other than the Moon? I understand that the planet Venus can be quite easily seen at certain times and latitudes, but I am not astronomer enough to state facts.

1296516.  Wed Sep 26, 2018 6:24 pm Reply with quote

Smoking the local 'erb?

1296641.  Thu Sep 27, 2018 7:50 am Reply with quote

Generally mirages are caused by light being bent when passing through layers of air of differing densities. These layers of air are usually horizontal due to the effects of gravity, so I'm not sure that a mirage could work in the vertical plane.

Since the story concerns seeing the moon during the day, I suspect a more likely explanation is that the first sighting was a mistake. During the day, the moon is quite dim and not always easy to spot. I could imagine that a small patch of cirrus cloud could be mistaken for the moon, only to disappear due to air currents or solar heating, whereupon the real moon is spotted in a different part of the sky.


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