Venerean phases
Venus has been very bright in the evening sky lately, as you may have already noticed. A friend of mine was playing with an astronomy program on his iPod Touch while we were walking the other evening and asked what «that bright star» was. I said that an object in the sky as bright as the one we were looking at could only be Venus (correct) and I speculated that Venus might be brighter when farther from us, because we’d be seeing more of the bright side (not correct. Sorry!)
Said speculation was wrong because I’d underestimated the change in apparent size of a planet that always looks like a point of light to the naked eye. Venus orbits at about seven-tenths as far from the Sun as we do. When Venus is at its closest to us it is about 0.3 Astronomical Units (one AU is the distance from the Earth to the Sun) which is very much closer than 1.7 AU so even in crescent phase the bright side of Venus takes up more space in the sky than when it is full on the other side of the Sun. (I’m not going to bother with the math for how far away Venus would be at various points on its orbit relative to us. «A lot closer» is good enough for me.) This appears to be true until the crescent gets very thin.
An Astronomy Photo of the Day from a couple of years ago illustrates this.
It seems that Venus is approaching as near to us as it ever gets. I’m assuming that for my purposes I can disregard the elliptical nature of Venus’ orbit because Wikipedia says that Venus’ orbit is much closer to circular than ours. Venus will transit the Sun in the beginning of June and we pass perihelion in the beginning of July, so I think it’s fair to say that Venus is pretty darn close now and will be nearly as close as it ever gets in June.
(I could do the math for this as well, but my math skills are so rusty that it might take all afternoon and I’m too lazy to do that right now.)
I took my binoculars out to look at Venus last night to see whether I could see a crescent shape. I thought that I glimpsed the crescent through my 12x binoculars, but owing to them being binoculars it’s difficult to get a perfectly sharp focus in both eyes at the same time. It’s also very difficult to find an adequate surface to use to keep the binoculars steady. Even propping my arm against the ground there was enough movement in my hands that I didn’t get as good a look at Venus as I’d like. It’s difficult to know whether my eyes actually resolved the crescent shape or if my mind filled in the blank from seeing motion «blur» from persistent vision or monochromatic aberration in the binoculars’s lens (or my eye, for that matter.)
It’s too bad that I don’t have enough magnification to see clearly the second-nearest object in our solar system. Living in the City means fighting to see through light pollution, and I don’t have anything stronger than the 12x binoculars. I’ve wondered at the possibility of getting a telescope, but it would have to be a pretty small one in order to be transportable with tripod on my motorcycle, and I’d need the motorcycle to get the ‘scope far enough away from the City that I’d get dark skies.
Venusian.…
…is the far more commonly-used adjective. Venerean, venerian, and venerien are generally considered obsolete. Interesting article, though, and good to hear you are still looking up!
You should be able to see the crescent shape starting with about 8x binoculars. My arm-held 6″ f/4 rft shows it clearly at 19x. Maybe I’ll take my 7×50 binoculars out the next time it is clear. See! You’ve inspired me!
One interesting point is that Venus is bright enough to cast a shadow here – on moonless nights, of course. The first time I ever noticed this was at Stellafane. I was in the Porter Turret with the door open, and as I glanced away from the eyepiece I saw the bright outline of the door on the floor and wall. My first thought was that it was an airplane, but it didn’t move, so I went to the door and looked. Venus, in all her glory!
Dad
Venereal?
I forget whether it was Neil deGrasse Tyson, but someone whose lecture I listened to in the last few years said that the correct term should be «Venereal» but that it isn’t used because of other connotations (though it’s all named for the goddess of love.)
Good to know that seeing the crescent was probably not just my imagination. It would still be great to see with something that is not hand-held. It wouldn’t take very much more magnification to make it a really great sight.
Tests
Tonight I went out with several sets of optics to view Jupiter. I left the big boy in the shed as the answer to whether you can see Venus’ crescent with a superb 12″ scope on a steady mount seems rather obvious. First I tried my handheld 6″ f/4 at 19x and 30x. It was harder than I remembered getting the view steady enough, but Venus was clearly crescent shaped. (Handheld is a little bit of a misnomer. I use a shoulder strap and cradle the tube assembly tightly across my chest with both arms.) Next I tried my excellent Fujinon FMTR 7×50 Polaris binoculars. It was not easy, but I finally was able to convince myself that I was not just imagining the shape. Steadiness was not much of an issue, but the image was pretty small. Finally, I took out my Swift 60mm 15x-60x spotting scope. It has a small tripod for use as a target spotting scope when shooting prone, so I laid in the road and used the tripod. It was simple, clear, and steady at the 60x end, but the optics aren’t as good at the 15x end, so focussing was a bit of a challenge. After focussing, I was able to stand and handhold at both 15x and 60x and see the crescent cleanly.
So, IMHO you should have been able to see the crescent in your 12x binoculars. BTW, I usually focus on stars before turning to Venus. It is soooooo much easier to tell when a pinpoint is smallest than to tell when a blob is sharpest.
Dad
Wait. Jupiter?
Wait. Jupiter? According to the GoSkyWatch app on my iPhone, Jupiter is directly on the other side of the Sun. Maybe I’ll have to consult another source for locating planets. If you can see Jupiter, GoSkyWatch has a bug.
It was cloudy last night but tonight I’ll try focusing on a star first and then check out Venus. Thanks for te suggestion! Though it does look pretty hazy to the West. We might have fog/clouds roll in this evening like we did yesterday.
Where’s your scope?
Your 4″ should do a great job on Jupiter.…..
Dad
The 4.25″ ‘scope
My telescope is in Albany. It’s not terribly portable so even if I had it here in California it wouldn’t get used very much. I think I’m going to need something with a really short focal length.