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PRINTA Daytime Moon?
Ever wonder why you can sometimes see the Moon when it’s still daylight out?
Actually, you can see any celestial object in the daytime sky, provided the object is bright enough and large enough. The Moon fills both requirements. Another example is the planet Venus, which is often readily visible during the daytime, especially when it is near its greatest brilliancy. Because Venus is no more than a speck in the sky, though, you have to know exactly where to look against the “sea of blue sky” in order to find it.
Supernovae, massive stars that blow themselves to bits at the end of their life cycles, have also been visible during the day. Two famous examples are the Guest Star of Taurus in 1054 and Tycho’s Star of Cassiopeia in 1572.
Brilliant meteors have, on occasion, been seen flaring across the daytime sky. One such meteor blazed a path across the Grand Tetons in August of 1972, and was seen by tens of thousands of people. A few comets have also been seen in the daytime. The Great Comets of 1843 and 1882 could be seen even when they were right next to the sun. They likely were each at least 100 times brighter than the full Moon. In fact, the 1882 comet was compared to the flame emitted by a smelting furnace.
So, if the Moon is bright enough to be seen by day, why can’t we see it every day? When the Moon is full, and at its brightest, it sits directly opposite the Sun in the sky, which means it is below the horizon while the Sun is up. The New Moon rises during the day, but sits too close to the Sun to be seen. It sets at night, which is why the night sky is dark during the New Moon. It’s only as the Moon gets close to its quarter phases that the conditions are ideal for it to be seen during the day. That is, it is bright enough, far enough away from the Sun to be seen, and rises or sets during daylight hours. When all of these conditions come together, and when the sky is clear enough, the Moon becomes visible during the daytime.
Caleb Weatherbee is the official forecaster for the Farmers' Almanac. His name is actually a pseudonym that has been passed down through generations of Almanac prognosticators and has been used to conceal the true identity of the men and women behind our predictions.
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If you notice a hole in the upper left-hand corner of your Farmers' Almanac, don't return it to the store! That hole isn't a defect; it's a part of history. Starting with the first edition of the Farmers' Almanac in 1818, readers used to nail holes into the corners to hang it up in their homes, barns, and outhouses (to provide both reading material and toilet paper). In 1910, the Almanac's publishers began pre-drilling holes in the corners to make it even easier for readers to keep all of that invaluable information (and paper) handy.
3 comments
New to our first grade science core this year is a study of the moon in the daytime sky. How do I know at what time of the day and year it will be most visible?
Hi Joey,
Several ways you could do this:
1) The easiest is to locate Venus right around the time of sunset. Carefully note its position in the sky relative to foreground and/or distant objects. Now head out the following day about five or ten minutes earlier and concentrate on that particular part of the sky that you were looking at the day before. You should be able to pick up Venus appearing as a tiny white speck against the blue sky . . . even though the Sun is still above the horizon.
2) Wait until the crescent Moon passes through the same part of the sky. The Moon is a much easier object to see in the daytime because of its larger angular size. If you know where Venus is relative to the Moon, you should be able to locate it against the daytime sky. This month, Venus will appear closest to the Moon on July 14. Check out this diagram from Sky & Telescope magazine:
http://www.skyandtelescope.com/observing/ataglance
3) A somewhat more complicated method is find a star in the sky that has the same declination as Venus. Then, based on the difference in the hour angles/right ascension between the two objects, Venus can be readily located. Unless you’re into the technical aspects of astronomy I won’t get into an explanation as to how to do this . . . but I’ve used this method many times to find Venus during the middle of day through my telescope.
Of course try to do this on a day when the sky is clear with no clouds or haze around. And it would also do yourself well to use binoculars to scan around that part of the sky where you presume Venus is located; the best type to employ for this job are 7 x 35 binos with a wide angle (11-degree) field, but you can also use regular 7 x 35 or 7 x 50 binos as well.
Good Luck!
Joe Rao
Staff Astronomer
The Farmers’ Almanac
Where can you look to find Venus during the day.
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