See Venus In The Daytime? No Way … WAY!

At 2:30-3 p.m. local time, Venus will lie about three outstretched fists to the lower left of the sun and two fists above the southern horizon. Illustrations created with Stellarium

This illustration looks a little weird with fists floating in the sky, but I’m hoping it will serve a useful purpose. The other day we talked about how finding Venus is difficult this month because it’s so low in the west after sundown. Venus, like all the planets, follows the sun’s path in the sky called the ecliptic. The particular portion of the ecliptic it’s on right now makes a very low angle to the western horizon resulting in poor placement for northern hemisphere sky watchers.  Why not try to find Venus when it’s higher up and better placed? Great idea Astro Bob, except the only way to do that is when the sun’s up. Exactly.

Venus looks like a crescent moon this month. Unlike the moon, it's completely cloud-covered and appears pearly white in binoculars and telescopes.

Venus is bright enough to be visible all day long if you know just where to look. And right now, since the planet is relatively close to Earth, it’s large and quite bright. Should you find it, take a look in binoculars. You might just be able to discern its phase – it looks just like a miniature crescent moon.

Go out and face due south around 2:45-3 p.m. To find the planet, you’ll need a clear, deep blue, haze-free sky and a bit of persistence. Reach your fist toward the sun (remember never to stare directly at the sun, as it can damage your retina) and move it three widths to the left and below. Venus is two fists above the due south horizon. Look for a tiny, bright white spark. Some of us older observers have to contend with those dark floaters swimming around our eyes. Don’t let them get in your way. I keep going and try to see past them. Once you latch onto the planet, you might be surprised how well it stands out after all. It never ceases to amaze me that you can see Venus in a blue sky. Another way to spot it is to start with binoculars. Make sure they’re focused for Venus by first focusing them on a cloud in the distance. Follow the directions and search the location to find the planet. Your field of view is smaller, but binoculars will make it pop out better.

Once you’ve found Venus, keep the planet in view while carefully lining it up with a nearby tree or power pole. That way you can easily find it again in case you lose it. Congratulations on a tricky observation! Now bring your binoculars to the subject and see if you can make out that crescent. While you can try other times to find the planet, 2:30-3 p.m. is best because that’s currently when Venus is highest in the sky and due south. I’ll be trying today to spot it and share my report tomorrow.

Last night was one of the quietest, finest nights I’ve ever been out observing. The only sound was the occasional leaf tumbling from tree to ground, tapping on branches as it fell. Silence is as enriching as studying a planet in detail or surveying a galaxy cluster. Cassiopeia was way up there and Comet Hartley 2 was plainly visible in binoculars. Now you’re going to think I’m “Cassiopeia-crazy”, but we’re going to use that constellation again to find the curious star Algol in Perseus the Hero.

Algol’s name originates from the Arabic Al Ra’s al Ghul which means “the demon’s head”. The Greeks knew the star as the head of Medusa; one look into her eyes would turn a person to stone. All this scary stuff perhaps hints at Algol’s habit of fading and rebrightening with precise regularity every 2 days 20 hours 49 minutes.

Algol is really two stars but too close to one another to separate in a telescope. The larger star, Algol B, periodically eclipses the smaller, hotter star. Illustration: Bob King

Much later, it was discovered that Algol is an eclipsing binary or a pair of stars that revolve closely around one another. Algol A is a white star much hotter than the sun, while its companion, Algol B, is a larger, cooler orange star. Every 2.87 days Algol B passes in front of Algol A for about 10 hours, covering or eclipsing 80% of the star and causing the whole system to dim noticeably. Sometimes eclipses happen at 3 a.m. or in the middle of the day, but tonight the middle of the eclipse – when Algol is faintest – occurs at 9:28 p.m. Central time. The star remains dim for an hour on either side of eclipse. Then as Algol B slides past A, the system gradually brightens back up to normal.

Look 1 1/2Â outstretched fists below the lower end of the W of Cassiopeia to find Mirfak. Algol is "four fingers" to the right and below Mirfak.

If you’re out early tonight, use Cassiopeia to take you to Perseus’ brightest star Mirfak and then on to Algol. Midwestern observers will notice that Algol is only about as bright as nearby Rho Persei from around 8:30 to 10:30. Later its brightness will be nearly that of Mirfak. If you live in the western states, Algol will be past minimum and growing brighter as night begins. East coasters can watch it fade to minimum if they check as soon as it gets dark. For the Midwest, Algol will be around minimum at the start of night and brighten up later.

If you don’t feel like staying up that late to find out, simply take note of Algol’s brightness early tonight and then compare on the next clear night. The difference – more than a magnitude – is very obvious. Careful though, don’t stare too long at the demon’s eye. I don’t want to be responsible for any of you turning to stone.

6 Responses

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  3. Stephen Buckland

    Greetings Bob,
    There has been a few pictures taken of what is being called by some planet X from Australia.
    Is Venus visible during the day now (April 2011)?

    1. astrobob

      Hi Stephen – While there are probably many asteroids way out beyond Pluto awaiting discovery, no large planet beyond Pluto has been photographed or found. There’s always a chance one might be there awaiting future discovery. Venus is out all day but rather near the sun. You can catch it very low in the east before sunrise.

  4. Xavier

    Hi Bob, thanks for the post! If you think about it, Venus is much brighter and more reflective than out moon, and we can easily see our moon during daylight hours, right? The trick with Venus, as you point out, is that its disk is much smaller in the sky than the moon. The other ‘trick’, of course, is that Venus is normally too close to the sun to look for. Right now, however, Venus is quite far, so thanks for your “handy” diagram to find it! -X

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