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brightness of Venus
ncc1701d
post Dec 21 2007, 07:28 PM
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I was wondering.
If Venus reflects 70 percent of the sunlight that hits it.
If I was in spaceship on approach to that planet could I look at it with the naked eye out the window and not get blinded?
Would I have to at least use sunglasses?

I am wondering to how much brightness reduction is going on when processing the images before they are release to public or analized.
thanks
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ngunn
post Dec 22 2007, 11:14 PM
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I would recommend sunglasses at least. Even at Earth's distance from the sun bright clouds or snow are bright enough to cause discomfort. At Venus the intensity would be about double. We evolved in warm latitudes where the brightest thing around was sand.
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ugordan
post Dec 23 2007, 12:04 AM
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If you were in a spaceship, even Earth would appear almost uncomfortably bright (at a distance to render a planet a small orb) due to the fact the eye was trying to compensate for the blackness of space. Venus would, by far, be brilliant to human eyes and you'd want more than good sunglasses, I'd think. In fact, being closer to the planet you might actually feel the sun's heat reflecting off its clouds on your face.


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edstrick
post Dec 23 2007, 10:31 AM
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Something I've worried about is a hazard when you go beyond Earth's orbit. Sun-blindness.

People with normal eyes can look at the sun. Staring at it's bad, but evolution's prepped us to be able to glance at it or have it in our peripheral vision without frying our retinas in a hurry.

When you go out to Mars orbit and beyond.. the sun gets smaller.. and dimmer... but not with any lower surface brightness.

As you get out to the belt and Jupiter's orbit, the sun's getting really small, with a total angular-arc-minutes of area like the sun during the near-total stages of a solar eclipse... THE ONES WHERE PEOPLE FRY THEIR RETINAS!.

The problem is that as total brightness drops, the iris starts to open a bit from sun-safe maximum constriction.. and the brightness per square micrometer on the retina rises to "sizzling" levels.

People exploring beyond the sun may need active, smart eye-tracking, eye-shielding self-opaquing optics in suite helmets and the like, and windows that automatically darken or blur when the sun is visible.
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Stu
post Dec 23 2007, 10:41 AM
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QUOTE (edstrick @ Dec 23 2007, 10:31 AM) *
As you get out to the belt and Jupiter's orbit, the sun's getting really small, with a total angular-arc-minutes of area like the sun during the near-total stages of a solar eclipse... THE ONES WHERE PEOPLE FRY THEIR RETINAS!.


... brings to mind a true story. 1999, August... there's a total eclipse of the Sun visible from the extreme SW of the UK, everywhere else in the UK will see a good partial eclipse. As Secretary of my town's astro society I've organised a big "Eclipse Watch" event (later attended by over 1000 people, it was fantastic!!!) and am being interviewed on local TV and radio a lot about it, and have info pieces in all the local papers too, stressing again and again and again the safety aspects of observing the eclipse: only use eclipse glasses or pieces of VERY dark welding glass if they're safe... don't use smoked glass, CDs, Penguin or Kit Kat foil wrappers or anything else like that, they're not safe at all, and if you can't get any glass or glasses then prick a hole in a piece of card to make a "Pinhole projector" and watch the eclipse by projecting the Sun's image thru the card onto a wall. I figured I had all the bases covered. Common sense, right?

The night before the eclipse, my phone rings, and no surprise it's another caller asking for eclipse watching advice. "I saw your piece in the paper, and I have bought some eclipse glasses," the lady tells me. "But do I prick a hole in BOTH sides to look at the Sun through, or just one..?

rolleyes.gif


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J.J.
post Dec 23 2007, 03:46 PM
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A pretty interesting question, one I've speculated about myself...

I did a little back of the envelope calculation, using the differences between Earth and Venus's albedos, comparisons between the Moon and Earth's diameter a one lunar distance (as a baseline), the different solar constant between Earth and Venus, basic geometry, and finally the distance of geostationary orbit (for Earth, anyway) as the final comparison.

My very crude results suggest that at a distance from Venus equivalent to geostationary orbit around Earth (~35,800 km), Venus would be roughly 28,000 times brighter than the full Moon appears from Earth. Though its light would be spread over an area about 1,570 times greater, it would still be almost 18 times brighter per square arcsecond than the full Moon. In sum, I do think it would be hard on the eyes, and probably dangerous for long periods.

Feel free to check my figures, people...

Addendum:
A slightly less aggressive calculation still suggests Venus would be about 10 times brighter than the full Moon per square arcsecond...


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dvandorn
post Dec 23 2007, 04:50 PM
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I'd just like to bring into this conversation the experience of the guys who have dealt with something similar -- those who went to the Moon.

Now, the Moon is a lot darker than Venus, by something like an order of magnitude. It reflects a lot less light. But astronauts who operated in orbit around it, or on its surface, regularly wore sunglasses, and skipped the sunglasses at their own peril.

As one example, John Young, on Apollo 16, decided he didn't need sunglasses when preparing for ascent from the lunar surface, and ended up riding into orbit in an almost completely sun-blinded condition. Per his own statements in debriefing, Young couldn't really see anything during ascent, and he blamed it on sun-blinding from the brightly illuminated surface. (Granted, the highlands site where Young and his LMP, Charlie Duke, had landed was of a higher albedo than other landing sites, but not that much higher.)

So, if the Moon can cause sun-blindness in those who don't take the proper precautions, I can just imagine how much greater the problem would be in orbit around Venus.

-the other Doug


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J.J.
post Dec 23 2007, 05:29 PM
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^
Ditto--and the Sun is twice as bright at Venus's distance, to boot.


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Mayor: Er, Master Betty, what is the Evil Council's plan?

Master Betty: Nyah. Haha. It is EVIL, it is so EVIL. It is a bad, bad plan, which will hurt many... people... who are good. I think it's great that it's so bad.

-Kung Pow: Enter the Fist
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JRehling
post Dec 23 2007, 10:39 PM
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The John Young incident is interesting, and not one I'd heard before. And a priori, it's somewhat surprising. After all, the Earth is lit almost as brightly as the Moon, and in many places has higher albedo. And sunglasses are not de rigeur on Earth.

My guess is that the black sky is to blame. With the visual field partly taking in sky, the difference between the Earth's blue sky (which is not so bright as to cause damage with sustained foveation) and the utter blackness of the lunar sky should make a difference in pupil diameter. I guess that staring down at the Moon would be less of a problem than doing a lot of sky gazing with a few quick glances down at the Moon.
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dvandorn
post Dec 24 2007, 07:45 AM
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Many of the Apollo astronauts chose to wear sunglasses when doing a lot of "out of the window" stuff both in lunar orbit and on the surface -- and, of course, the LEVVA visor assemblies had built-in sunglasses (the outer gold-coated visor).

Pete Conrad almost landed on the Moon wearing sunglasses inside his bubble helmet, but all of the standard-issue sunglasses back then were the green-tinted kind, and Pete decided rather late that the green shading washed out too many details. But he indeed removed his helmet and took off his sunglasses just prior to descent.

As for Young, recall that 1) the Descartes landing site was in one of the highest albedo terrain units the Moon has to offer, and 2) by the time they lifted off, Young and Duke were sitting under the highest Sun angle anyone in Apollo would ever see from the surface (owing to their three-rev, six-hour landing slip). Add to that the airlessness, which not only gave the pure black sky in contrast to the brightly lit surface but also allowed full unfiltered Sunlight to beat down. Any place on Earth lit with that kind of unfiltered Sunlight would likely make you "snowblind," as well.

-the other Doug


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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Guest_PhilCo126_*
post Jan 2 2008, 05:42 PM
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Guests






Talking about a bright Venus, ESA made a website on which observers can contribute and download their images of our sisterplanet:
Wanted: Your pictures of planet Venus:
www.rssd.esa.int/vaa
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Guest_PhilCo126_*
post Nov 25 2008, 05:42 PM
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Guests






Looking South these winter evenings, You'll notice 2 bright spots, the lower one is Venus, the upper one is Jupiter.
Good binoculars show Venus as a half disk and Jupiter's moons were on the left side of the gas giant this evening.
Remember that by the end of the month, the Moon, Jupiter and Venus will be very close together.
Best time to watch: For West-Europe: 16:30 GMT
smile.gif
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Stu
post Nov 25 2008, 05:47 PM
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This is how they looked this time last week from n California...

Attached Image


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CAP-Team
post Nov 26 2008, 10:04 PM
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Yes, Venus and Jupiter look very nice in the evening sky this month!
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scalbers
post Nov 27 2008, 06:55 PM
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I suppose I need sunglasses just being on Earth's surface in Colorado where there is more UV than at many other locations. And I really need them when flying in an airplane looking down at bright clouds. So I can further imagine how they would be needed in orbit around Venus.


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