General Questions on Jovian/Martian Shadows on Earth

[Via Lactea]

I've no doubt lots of people on here will have heard of, read about and discussed the then-14 year-old Laurent Joli-Couer's experiments culminating in the successful imaging of a shadow of a gnomon cast by Jupiter back in 2011. I can't locate a thread, it was two years ago however. If there has been an old thread on this topic on here that someone knows of, a link would be very greatly appreciated. Anyway, for reference, here is the experiment I'm talking about:

blogs.discovermagazine.com/badastronomy/2011/11/18/young-astronomer-captures-a-shadow-cast-by-jupiter/#.UmcPBBBdAic

I was wondering, first off, if people on here have had any (or even many?) experiences with or images of Venusian or Jovian shadows, and how faint or dark these were. This is a facet of astronomy that fascinates me. Not just because light and photons (and all that!) are fascinating anyway, but the idea of a celestial body casting your - admittedly faint - shadow is one that I'm just enthused about. Im fairly new to serious astronomy, so any anecdotes would be appreciated!

Previous to reading the above article I had assumed that only the Sun, Moon and Venus were capable of casting noticable shadows upon the Earth. Wikipedia claims that the app mag. for human-noticable shadows is ≤ -4 here: http://en.wikipedia.org/wiki/Shadow N.B the source for that claim is just the original article above!)

There seems to be some confusion on this however, as Wikipedia also claims here http://en.wikipedia.org/wiki/Apparent_magnitude that the maximum app mag. of Jupiter is -2.94, well above the -4 maximum a/m previously claimed in the previous link. Mars is not far behind, with a maximum a/m of -2.91.

So is there a - pardon the pun - faint chance that Mars can cast shadows under the optimum conditions also? Someone on this thread from another site claims that it can, and uses a link to the anecdotal 1905 claim to back it up.) Any thoughts or opinions on this? And if so, should the maximum apparent magnitude for casting shadows be recalculated?

Finally, I am now of the understanding that under the right conditions, the collective or "integrated" magnitude of the stars in the night sky can reach a maximum of -6.50. This raises more questions, as presumably the collective, albeit diffuse, light of the surrounding stars could cast shadows too. Any thoughts, experience or guidance on this would be muy apreciado

Steven

[Stu]

Interesting post Steven. I can't add much but I have certainly heard reports of the Milky Way being bright enough to cast shadows when in extremely dark locations. I've not experienced it myself, would love to though!

I guess, ultimately, if you are somewhere dark enough with perfect dark adaptation then Jupiter and others may potentially do the same.

Cheers,

Stu

[Stu]

Knew I'd seen it somewhere. This is from the Stephen O'Meara book on Messier Objects. Bottom of the first page, top of the second.

http://books.google.co.uk/books?id=jis4evHuuzUC&pg=PA27&lpg=PA27&dq=o'meara+milky+way+casting+shadow&source=bl&ots=rvqUjF-G2_&sig=GbvK-TlCgPlpmyvrQ7bSbJueAb0&hl=en&sa=X&ei=gXxnUoGDCJe-4AOPiIGoBA&ved=0CC0Q6AEwAQ

The Bortle Scale also references the same thing.

http://en.m.wikipedia.org/wiki/Bortle_scale

[michael.h.f.wilkinson]

I have seen shadows cast by Venus, but not by Jupiter. It is one thing for a shadow to be imaged successfully, quite another for us to notice it. I would think for a shadow to be noticeable the object should be near point source, and considerably brighter than the sum of other (point) sources. At -4 Venus qualifies quit easily, being as bright as 100 mag 1 stars. At mag -2(ish) Jupiter can only outshine about 15 mag 1 stars, which means the shadow is going to be quite weak.

[Via Lactea]

Just want to apologise for my lateness and thank you both, Stu and Michael, for those responses. I pored over that link Stu, truly enlightening (if you'll pardon the pun) and of great magnitude (OK, now I'm just punning for the sake of it!) I'm having another look at it just now, cheers to you... it's sharing info like this that makes this forum what it is. And Michael, that's a valid point - imaging doesn't equal "noticing", perhaps I am being too idealistic in my ideas of the importance of magnitude. Anyhow, cheers guys... I've a feeling I'll be asking questions on this topic again in the future as I study it more and more

[Ant]

Pete Lawrence posted several threads here on SGL a long time ago showing the shadow of a bunny rabbit (I believe) cast by Venus.

But it was a long long time ago.

Ant

[Ant]

Can't find the threads on Sgl, but have found them on Pete's site.

http://www.digitalsky.org.uk/index.php?wrapname=projects⊂=shadow1

Cheers

Ant

[Via Lactea]

I really seriously can't thank you enough for that link, Ant. Cheers - I'm already reading it!

[Via Lactea]

Fantastic article. The pics alone were amazing, couldn't believe how big Venus appeared when photographed.

Hmmm... and now I'm suddenly wondering whether Jupiter and Mars in conjunction have a raised combined magnitude, I assume they must. I have a feeling I may end up contacting Pete for advice!