Venus shines at magnitudes ranging from -3.8 to -4.9, depending on its distance from Earth and the percentage of its disk illuminated by the Sun. To give you a scale of what that means, the brightest star in the night sky is Sirius, at -1.5. Every magnitude step is a multiplication by a factor of 2.512 in brightness (as 5 magnitudes part objects that are a factor of 100 in brightness, and 2.512 is the fifth root of 100), so the minimum brightness of Venus is 2.512^2.3, or something like 8.3 times more than Sirius; the maximum is about 23 times more. As our senses work with a logarithmic scale of the stimulus, though, these factors mean little - Venus just looks much brighter than a star, and that's all. But that's enough to make it "punch through" a clear blue sky.
I have observed Venus in daylight several times, for fun or in occasion of special conjunctions with other celestial bodies. Yesterday I could find it very easily almost at the zenith, as it was close to a crescent Moon and so I knew where to look. But today, I was able to not only find it, again close to the moon (although in a different configuration as the moon moves by about 15 degrees per day), but with some effort, I was able to also see Jupiter!
Jupiter is all another matter with respect to Venus - right now it is not even at its brightest, and it shines at about -2.0 magnitudes - only little more than Sirius. I was convinced that it would be extremely challenging to see it in daylight, if not plainly impossible. In fact, experts say that it requires perfect conditions and a Sun-Jupiter angle of 90 degrees, which is the region of sky where polarization makes the sky less bright. But even under those "best" conditions, one needs a hawk's eye and a lot of patience, plus to know exactly where to look.
These days Jupiter is not in quadrature - rather, it is at about 40 degrees from the Sun, which is the brightest area of the sky. But luckily, the Moon and Venus provide a good guidance to look exactly where the planet is. I tried with no luck for a while during the afternoon, until - about half an hour before sunset - I was finally able to see it. Steady. It "popped out" as I watched exactly in its direction. It is not only a matter of direction, but also of focus: with no object to fix your focus to, you are likely to drift away from perfect focus, which strongly deteriorates the signal-to-noise ratio of the planet's image.
Indeed, it is after all the good old signal to noise issue: the sky has some background brightness, and the star or planet just "adds" some extra photons, in a very confined area (the "point spread function" as seen from your eye). In principle, therefore, *any* star produces a surplus of photons; but in practice, their signal is washed out by background fluctuations. Pretty much like searching for a rare particle in a mass histogram, if you are a particle physicist ;-)
I am obviously quite proud of my achievement of today, but I figure it is not after all too difficult, and I guess that if one can help oneself with a pair of binoculars (Jupiter is easy to find with binoculars in daylight if you know where to look) then it must be doable almost in any circumstance, if the sky is clear. So, the challenge is on now - can you do it ? I would be happy to know. Tomorrow the Moon will be far away from the Jupiter-Venus duo, but finding Venus is not too difficult, and it should provide you with the right guidance to find Jupiter as well...
Below is a picture I took after sunset of the Moon - Jupiter - Venus trio as I could see them from Ibiza (where I am currently spending some vacations). Okay, the pic is rotated - I did not bother changing its orientation as it does not really matter.
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