Well, not the last chance in your lifetime. But you have less than a week left in Venus’s current run as “evening star” for one of visual astronomy’s greatest challenges — to see the crescent Venus with nothing more than your eyes. No binoculars. No telescope. To aid you in your quest I want to share a new technique briefly mentioned by Sky & Telescope columnist Fred Schaaf in the magazine’s May issue.
I stared at Venus a week ago trying to eke out a crescent but couldn’t. It looked spiky to me, a little like a porcupine. I squinted but that didn’t help either. Binoculars show the phase beautifully but my eyes were hopeless. Then I heard that if you look at the planet through a pinhole device it reduces the glare and porcupine spines. So I tried it on May 21. I have small metal eyepiece barrel with a neat 1/16-inch (1.6 mm) hole drilled through it. I held this up to my eye and peered at Venus through the tiny aperture and lo and behold the planet appeared much sharper.
The same principle applies when you want to get more of a scene in focus with your camera. If you decrease the size of the aperture the light passes through it will increase the camera’s depth of field, making both foreground and background sharp.
Now that Venus appeared sharper could I see the crescent? The planet spanned 53.5 arc-seconds at the time or 6.5 arc-seconds shy of the theoretical naked-eye limit of 60 arc-seconds. Close enough. A word about terminology. One degree (1°) equals 60 arc-minutes, and one arc-minute equals 60 arc-seconds. The full moon is 0.5° or 30 arc-minutes wide so Venus is about 1/30th the apparent size of the full moon right now.
I peered through the hole on and off for 10 minutes, and this is what I discovered. While I couldn’t convince myself of seeing the crescent I did notice that Venus wasn’t round. Instead of a dot it appeared like a bar or short streak of light tilted on its side like this: / … only a little shorter.
Occasionally, I thought I saw the crescent with its horns pointing in the right direction (up) but a few moments later they looked pointed down in the wrong direction. So while I couldn’t see a precise shape, at the very least discern I could tell that Venus was elongated and tilted in the right direction. I’ve looked at Venus for over 50 years, and this was the first time I’ve ever seen a whiff of crescent.
I encourage you to try the same technique. Drill a 1/16-inch (1.6 mm) hole in a bottle cap and make sure you remove any excess plastic for a completely unobstructed view. For the best results try to find Venus as close to sunset as possible and then follow it down. A bright sky will temper the planet’s glare and make the shape easier to see. Although Venus is quite low it’s also a little bigger compared to when I saw it — almost 55 arc-seconds across.
I would love to hear about your attempt to see the crescent. Use the comments area here or send me an e-mail at firstname.lastname@example.org