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ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia

Observing crescent Venus (1 Viewer)

tenex

reality-based
Venus is a lovely thin crescent now. In any binocular (or at 20x in our recently acquired S2 scope) I can tell that it's a crescent, but it looks fairly thick, like a quarter moon. Only at higher magnification does it become clear how very slender the crescent has become. Why is this? It reminds me of how ~50x is also necessary to see a clear gap between the rings and disk of Saturn, although that strikes me as a rather different situation.

Unfortunately we're clouded out tonight, and probably tomorrow too...
 

Tringa45

Well-known member
Europe
Venus orbits the Sun in 225 days inside the Earth's orbit, so it can only be seen as a crescent near dusk or dawn. Open to correction here, but it's probably about to overtake the Earth on the inside, hence thinning crescent.
As Arthur points out, the planets are best viewed in twilight. Venus, being closer to the sun, has a surface brightness higher than the earth in daylight, so in scope or binoculars in a dark sky the image suffers from flare.
Mercury, being so small and distant is very difficult to locate and I had only "seen" it during its transit (with solar filter on my scope) in 2016.
A couple of years ago Mercury was close to Venus in the evening sky, which was helpful in finding it, and before it became visible Venus appeared as a perfect crescent in my 10x binoculars, much better than previous sightings through my scope.
I recall reading of an amateur astronomer who managed to locate Venus in daytime with his big Newtonian. He invited someone to take a look and this person refused to believe he was not viewing the Moon. :)

John
 

tenex

reality-based
The Venusian crescent is generally clearer when viewed in daytime, when contrast is lower.
Clouds have prevented me from trying to locate Venus earlier on for two days now, but the sky was still bright enough that Jupiter was barely visible, and in any case this doesn't address my question about effects of lower vs higher magnification which does not as far as I know change contrast.

...and before it became visible Venus appeared as a perfect crescent in my 10x binoculars, much better than previous sightings through my scope.
And this sounds like the opposite of my own experience... how were those scope views inferior?

Perhaps an illustration will help (from Wikipedia, Phases of Venus), although my background sky was not dark. In the scope at 50-70x I see something similar to the last two crescent images here; in 10-15x binoculars at the same moment the planet not only seemed brighter but the phase appeared thicker, somewhere in the middle of the sequence.
 

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Tringa45

Well-known member
Europe
And this sounds like the opposite of my own experience... how were those scope views inferior?
Just that the ambient light level was still relatively high when trying to spot Mercury. The view in that situation would of course have been better with the scope.
Venus' illumination and albedo are higher than the Earth's, so if one tries to observe in a dark sky, as I had done previously, the image gets washed out by glare.

John
 
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia

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