by MarkBour » Fri Apr 15, 2016 4:09 pm
Asterhole wrote:It was stated that Venus was FAR from the Earth and presumably yes, nearly opposite the Sun from us. It would be the only way we'd see a near-full phase of the planet - and we'd probably see it at its brightest.
I would just point out that "brightest" is a complicated matter in the end.
After wandering through a few Wikipedia and space.com articles on it:
I've come to understand that there are terms such as luminosity (visual and bolometric), brilliancy, brightness, and magnitude, but I don't quite have them fully sorted out yet. Also, astronomers do not have very many objects they observe that are luminous and large in the sky, so I haven't yet learned any terms for luminosity per unit solid angle. Such a term would be relevant to discussing the Sun, Moon, or Venus, and might be the term that you'd be correct with. (When Venus is near opposition, its disc may be sending more photons to your eye per unit solid angle than at any other time. But even that, I am not at all sure of. Perhaps someone will enlighten me.)
But in most uses of the terms, and in the effect on the eye of a human observer standing on planet Earth, I'd say that Venus is "brightest" when it is a 26-28% crescent, not when it is near full (as the aforementioned articles indicate).
[quote="Asterhole"]It was stated that Venus was FAR from the Earth and presumably yes, nearly opposite the Sun from us. It would be the only way we'd see a near-full phase of the planet - and we'd probably see it at its brightest.[/quote]
I would just point out that "brightest" is a complicated matter in the end.
After wandering through a few Wikipedia and space.com articles on it:
[list][*]http://www.space.com/23852-venus-shines-brightest-observing-guide.html , [*]https://en.wikipedia.org/wiki/Phases_of_Venus , [*]https://en.wikipedia.org/wiki/Apparent_magnitude[/list]
I've come to understand that there are terms such as luminosity (visual and bolometric), brilliancy, brightness, and magnitude, but I don't quite have them fully sorted out yet. Also, astronomers do not have very many objects they observe that are luminous and large in the sky, so I haven't yet learned any terms for luminosity per unit solid angle. Such a term would be relevant to discussing the Sun, Moon, or Venus, and might be the term that you'd be correct with. (When Venus is near opposition, its disc may be sending more photons to your eye per unit solid angle than at any other time. But even that, I am not at all sure of. Perhaps someone will enlighten me.)
But in most uses of the terms, and in the effect on the eye of a human observer standing on planet Earth, I'd say that Venus is "brightest" when it is a 26-28% crescent, not when it is near full (as the aforementioned articles indicate).