Friday, January 28, 2011

See Venus During the Day: January 2011 Edition

I know that this topic interests people since I see a slow but steady stream of searches that land on my blog that mention this topic. Therefore, since we have a good chance to see Venus during the day this weekend, I'll review how to go about it.

Venus is best seen during the day when it is far from the Sun in the sky. We call this greatest elongation. Venus passed greatest western elongation on January 8th and is still nicely separated from the Sun. Venus is hard to find during the day and it helps to have a nearby landmark to find it. The Moon provides a nice guide and makes a nice pass by Venus on January 29th. The Moon a waning crescent and sets late morning/early afternoon (depending on your location and time zone) so check sometime mid-morning is your best show. Here is a finder chart made for Tucson at 9:00am MST tomorrow.

The Moon moves about a half degree every hour (which is conveniently about the same as its diameter) so if you look earlier the Moon will be farther to the west of Venus and if you look later the Moon will be farther to the east of Venus. You can use the free program Stellarium to make a chart for your time and location.

Find the Moon and then slowly move your gaze toward Venus. Slowly scan the sky. There are a couple of tricks to finding Venus. First, you have to keep your eyes focused at infinity. When you look at the Moon, your eyes will focus at infinity. If you are conscious of your eyes focus point, you can keep it from changing. It may take a little practice, but it can be done. Looking at a blue sky, your eyes have nothing to focus on so the focus may drift if you are not paying attention to it!

Second, you have to look DIRECTLY at Venus. You want the image of Venus to form on your fovea, the part of your retina responsible for sharp central vision. You can't spot Venus out of the corner of your eye! It is amazing that you won't see it at all and then suddenly Venus pops into view when it his your fovea and is so bright and obvious you wonder how you missed it before. Don't be only get this view when you look directly at it!

Another trick is to stand near a building. You want to stand in a place where the building blocks direct Sunlight but you can see the Moon and Venus. Blocking the bright glare of the Sun helps.

If its your first time trying to see Venus during the day, you might try picking it up just before the Sun rises and track it over the course of the morning. That practice will help you in the future. The Moon will still relatively close to Venus on Sunday, so you can give yourself a test then!

If you have clear skies, there is no reason you can't see Venus anytime it is up and away from the Sun.

You can try this again next month as the Moon makes an even closer pass to Venus on February 28th.

Reprinted with permission from the Half-Astrophysicist Blog.


OrbsCorbs said...

It's winter in Racine. The sky is always cloudy. I briefly saw the afternoon sun the other day. I ran into the hall of my apartment building, shouting, "Rejoice, rejoice!"

hale-bopp said...

Yeah, I remember. Big part of the reason I wanted to move back south. If you got a clear day and I didn't copy this over, I would be kicking myself!

MinnesotaChick said...

Thanks for the notice! Cloudy here too, but I'll remember to look if the skies clear!