¡SkyCaramba! Weekly astronomy blog for the week ending September 8, 2012
Did you know you can see Venus in the daytime? You don’t need to look for it during a solar eclipse or get high above the atmosphere. You just need to know exactly where to look. It’s actually bright enough to be seen with the naked eye in the daylight from Earth.
The clouds in Venus’s atmosphere are highly reflective. You can immediately recognize the planet when you see it at night because it’s one of the brightest objects in the sky. About 70% of the sunlight that reaches Venus is reflected. Consider how it’s fairly close to the sun and you can understand there’s a lot of sunlight reaching Venus to be reflected.
Think about how the earth is fairly close to Venus. The light reflected from the second planet is dimmer the farther you get from it. But Earth is always less than two earth-sun distances from Venus.
Venus would actually be brighter if not for being closer to the sun than the earth. How’s that? Venus has its back or side turned to us much of the time. Just like the moon, which goes through phases because we see part of its dark side, we see Venus as a crescent or gibbous object when we see it in a telescope. Even when only a tiny sliver of Venus is visible in a telescope, it outshines nearly everything else in the sky. If Venus were as far away as Mars, we’d always see it in near full illumination.
Before you go looking for Venus in the daylight, let’s talk about safe observing. You’ll need a pair of binoculars to get started. Once you find Venus with them, you can take them away from your eyes and see the planet without them.
Because the sun is up there too, you want to make sure you don’t point the binoculars at it. You risk permanent blindness if you do. So always make sure you aren’t pointing them anywhere near the sun. The best way to do that is to find a building you can stand next to. Your house may be just fine for the task. Look for Venus in the building’s shadow.
The building will help you in another way. If the sun is shining on your face, your pupils will contract. While Venus is bright, letting your pupils dilate will help you find it a little easier.
Of course, the shadow has to be on the right side of the building. Right now, Venus rises a few hours before the sun. It’s west of the sun. So you have look for it while the building is casting a westward shadow. In other words, you’ll be looking for it in the morning.
Next, you’ll need to know about what angle Venus is at from the sun. In early September, it’s about 45°. That’s half way up one side of the sky from the horizon. If the sun has been up a few hours, Venus will be close to “high noon”. When you estimate the planet’s approximate position, scan the sky with your binoculars until you see a little dot standing out against the blue background. It may help if you focus the binoculars on a distant object first so Venus is more likely to be in focus too.
Don’t’ be disappointed if it takes several minutes of patient trying to find Venus this way. It’s possible a high flying jet or other object will catch your eye, but you’ll know that by the way it moves. Venus will just hang there in place. And once you succeed, take the binoculars away from your eyes. Don’t turn your head or eyes and you should still see Venus right there. You may stand in awe wondering why you never saw it in the daytime before. You’ll be even more awestruck a few moments later when you turn your head away, look back, and see Venus right there again.
I’ll stress again how important it is not to look at the sun, especially with binoculars. Have a safe view. ¡SkyCaramba!