Venus...

I see there people said its impossible to make a shape out when looking at venus.....i thought it was weird that i looked and thought cresent straight away.....best get a clear night soon as point the scope @ it :shock:

we all vary when it comes to eyesight, some can see better than others. I only recently got glasses for both reading and another set for driving. When i look up at the night sky now, stars are sharper and seem a little smaller. So as regard seeing a phase of Venus with the naked eye....just wonder, as there are people with poor eyesight (both genetic and age related) there are for certain, individuals with exceptional eyesight. - maybe a lucky few.

I wonder myself if you went back far enough in time to when the atmosphere was cleaner, and there was no light pollution, and if you got yourself the ideal observing site (like on a hill, and not by the sea), would you be able to discern a shape to Venus by naked eye? Sometimes, I think I can make out Jupiter as a round dot in the sky when it is at perihelion to us i.e. it is an ever so small blob. The last time I ever thought I'd seen that was in the 90's.

Seanie.

Venus' apparent angular size varies from 9.7 to 66 arcseconds as seen from Earth.

The theoretical resolving power of the *perfect* human eye (with a 5mm pupil - remember you'll only ever see Venus in twilight) is 20 arcseconds (555nm light - peak sensitivity of the eye.) However this theoretical resolving power does not take into account such optical aberrations as misconvergence or astigmatism, floaters in the eye, corneal damage, cataracts(!) or how well light sensors in the eye function.

Your only theoretical hope of seeing phase on Venus will be when it is somewhere between inferior conjunction (closest to earth) and greatest elongation from the sun and showing its thinnest crescent and therefore pretty close to the horizon... which means the atmosphere will probably scupper your chances anyway!

... but that doesn't mean you shouldn't try!

Phil.

PS - Venus is just 14 arcseconds in size at the moment... so no hope - not even theoretically - of seeing phase

Fred Schaaf, in his book "Seeing the Sky", discusses the visibility of the crescent phase of Venus with the unaided eye. There have been validated reports and it is possible to achieve the feat. As Philip says, there are a number of limitations and really, really good eyesight is a must.

Schaaf also discusses the other interesting observation of the Galilean moons of Jupiter. But for the glare of their parent planet, these moons would be naked-eye "stars". The limitations here are how far elongated they are from Jupiter at the time and attempting to somehow block the glare from the planet. Again, valid observations exist.

Others have seen stars and deep-sky objects much fainter than the generally accepted naked-eye limit of magnitude 6.5. I'm thinking observations of M81, a galaxy in Ursa Major, which shines at magnitude 7.8. Keen-sighted observers from exceptionally dark sights have seen stars as faint as magnitude 8.2 under documented conditions.

An interesting project for observers would be to use a 1x power telescope/finder and try and see some of the sights mentioned above

I bought a 4x binocular recently based on what Roger Sinnott wrote about them in Jan 08's Sky and Telescope. He said that you could see almost the whole of the constellation of Orion in them but with extra stars, and that the Pleiades really looked "tangled in a silvry braid".

atb,

John

I must have a look for that book thanks john....by any chance the 25x100 binos you have listed are they celestron??

Hi Tony,

The binoculars are made by Apogee but the 25x100 Skymasters are very similar to them. A variation of the Apogees have a filter wheel which you can use to spin built-in nebula filters but I've never tried them although have seen them at star parties. Very heavy binoculars so a strong tripod is a must.

"Seeing in the Sky" is just one of three similarly styled books that Fred Schaaf wrote. The one mentioned is subtitled "100 projects for the naked-eye observer" and is excellent. It covers lots of subtle sky phenomena that the naked-eye observer can follow including atmospheric optics, planetary motions, aspects of the Moon, and aurora (had to get that last one in!) Omitted are observing naked-eye sunspots and following artificial satellites but that does not detract from the book.

The other two books are "Seeing the Solar System" and "Seeing the Deep Sky" and are equally excellent in suggesting projects and guiding you through all aspects of observing various celestial phenomena.

Amazon UK have "Seeing the Sky" for as little as 25p!!! I'd recommend www.bookfinder.com and used.addall.com as two book dealer search engines which trawl not just Amazon but Abebooks, Alibris, and many other on-line sellers simultaneously.

Happy browsing!

John