Astro Bob: The crescent Venus is within your reach

"Astro" Bob King is a freelance writer for the News Tribune. Read more of his work at

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Venus reflects in a lake near Duluth, Minn. on May 11 at dusk. The star just above the planet is Beta Tauri also known as El Nath. Venus approaches the star in the coming nights but never reaches it because the planet is now sinking back toward the sun. (Bob King for the News Tribune)

Venus appears as a tiny crescent between tree branches yesterday evening (May 11) through a telephoto lens. You can easily see its phase in binoculars now. (Bob King for the News Tribune)

Have you noticed that Venus is starting to slide in the sun’s direction? It’s not quite as high up in the evening sky as it once was. I hate to say this but we’ve only got till the end of this month before our favorite planet disappears in the solar glow. Venus is headed towards inferior conjunction when it will swing between the Earth and the sun. That happens on June 3. Venus and Earth will be closest then but we won’t see it because it lines up almost directly in front of the sun.

Planets being planets they’re always on the move. In a couple weeks Venus will swing to the other side of the sun from our perspective and reappear low in the eastern sky at dawn. Right now it’s still the “evening star”. After June 3 it will transition to “morning star.”


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As Venus cycles around the sun very 225 days, it passes between the Earth and sun in inferior conjunction and on the opposite side of the sun in superior conjunction. During this time, the changing angle the planet makes with the sun causes it show phases just like the moon. At inferior conjunction, it’s closest and in crescent phase. (Bob King for the News Tribune)

Whenever Venus is near inferior conjunction we see it as a crescent for the same reason the moon is a crescent — the angle the planet makes to the sun is slight, so the sun lights only an edge. And because Venus is spherical like the moon and other planets its edge is curved, giving it a crescent shape. When Venus lies on the opposite side of its orbit from Earth it’s shaped like miniature full moon and appears very tiny.

But since it’s close to us right now it’s also BIG. Big enough to discern its crescent shape in as little as a 7x pair of binoculars. I looked at the planet yesterday evening (May 11) with my 8×40 pair about 5-10 minutes after sunset. I had no problem finding the planet at that time. It stood two-and-a-half vertical fists (25°) high in the northwestern sky. Once I got the planet in sharp focus I had no problem distinguishing the tiny, white crescent. It almost seemed as if I were looking at our own moon from a great distance.

This superb sequence of Venus starting in October 2016 (left) and ending in Feb. 2017, clearly shows its changing phase and size from gibbous to crescent. Shahrin Ahmad

You can do it, too. Grab your pair and go out shortly after sunset. Don’t wait until the sky gets dark. If you do Venus will be too shiny, and it will be harder to see its shape. A little light in the sky helps to lessen the glare of this mighty bright world. Also, you’ll soon notice that Venus is already dropping behind the trees if you wait till dark. Focus and see this little gem for yourself! As the month wears on Venus will grow even larger but at a cost — the crescent will thin and the planet will get trickier to spot in the twilight glow.

Tonight the planet spans 48 arc-seconds or 12 arc-seconds shy of one arc-minute (60 arc-seconds = 1 arc-minute). 30 arc-minutes adds up to the apparent size of a typical full moon. Before it disappears in twilight Venus will expand to 57 arc-seconds, almost big enough to see its crescent shape without optical aid. The human eye limit is 1 arc-minute, very close to the maximum apparent size of Venus.

While there have been anecdotal reports of people seeing the Venusian crescent at least some of these observations were made in error because Venus was a thick crescent at the time and too small to make out. But that shouldn’t stop you from trying. I plan to make the effort, too starting the third week of May. Be sure you watch no later than mid-twilight to avoid the glare issue again.


You may not be able to see the crescent no matter how hard you try (my hopes are low!) but you might at least notice that the planet doesn’t look exactly round — a hint of its real phase.

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