Tomorrow’s new moon foretells October’s solar eclipse

Tomorrow July 26, 2014, the invisible new moon will pass a few degrees south of the sun in the daytime sky. Stellarium

New moons aren’t much to look at. You can’t even see them most months of the year. That’s true for tomorrow’s new moon which will invisibly accompany the sun in its journey across the sky.

New moons occur about once a month when the moon passes between the sun and Earth. We can’t see them for two reasons: first, no sunshine touches the Earth-facing side when the moon lies in the same direction as the sun. It’s completely dark. From our perspective, the out-of-view lunar farside gets all the sunlight. Second, since the moon is nearly in line with the sun, it’s utterly lost in the glare of daylight.

The moon seesaws 5 degrees north and south of Earth’s orbit during its monthly cycle because its orbit is tilted with respect to Earth’s. Only when the moon crosses the plane of Earth’s orbit at the same time as a new moon do we see a solar eclipse. Illustration: Bob King

We normally have to wait two days after new moon – when the moon’s orbital motion carries it to the left (east) of the sun – to see it as a thin crescent at dusk.

Most of the time the moon passes north or south of the sun at new phase because its orbit is tilted 5 degrees with respect to Earth’s. But 2.4 times a year on average, new moon coincides with the time the moon’s seesawing path slices through the plane of Earth’s orbit. For a brief time during that crossing, all three bodies are aligned and happy earthlings witness a solar eclipse.

If the alignment is imprecise, the moon blocks only a part of the sun, giving us a partial solar eclipse.  If dead-on, we see a rarer total solar eclipse.

View of the partial solar eclipse across the Upper Midwest a half hour before sunset on October 23. By coincidence, Venus will be near conjunction at the same time and only a couple moon diameters north of the pair. Seeing the planet in a telescope will still be challenging because of daylight glare.  Stellarium

On October 23 this year, the lineup at new moon will be a good if imperfect one with a maximum of 81% of the sun covered. The partial eclipse will be visible across much of North America; from the eastern half of the U.S. and Canada the event will occur near sunset, adding a touch of drama to the scene.

I wrote earlier that we can’t see a new moon. That’s only partly true. We mostly pay attention to the sun’s changing shape during solar eclipses, but the dark, curving bite working its way slowly across the sun’s disk is none other than the new moon seen in silhouette.

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

One thought on “Tomorrow’s new moon foretells October’s solar eclipse

  1. With New Moon so close, have you taken a look at Comet Catalina UQ4 lately? Hasit faded much? I thought about trying to find it with my 20 by 60 binoculars but it is probably too faint now.

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