Partial solar eclipse will be visible Thursday evening

A partial solar eclipse will be visible Thursday evening low on the horizon at sunset.

The eclipse begins at 6:00 p.m. for central North Carolina observers, although viewing the events along the East Coast will be a challenge.

Best viewing is further north and west. Observers in Alaska will get the best show (nearly 70 percent of the sun blocked), Florida pretty bad (only 12 percent), and no eclipse will be visible in Boston.

Here in central North Carolina, the moon will begin taking a bite out of the sun at 6:00 p.m. The show will all be over less than 30 minutes later as the sun sets completely behind the western horizon. This begins just 5º above the horizon, or about the width of 3 fingers stretched out in front of you. The better your view of the western horizon, the more you’ll see. If you are on the upper floor of an office building or your car is in a parking garage, this would be a good day to start your commute a little later.

Remember that it is never safe to look directly at a partial solar eclipse, especially this one.  No. 14 welders glass works well. Using a pair of binoculars to project the sun onto a sheet of paper is also safe. Morehead Planetarium handed out hundreds of eclipse glasses during the transit of Venus event in 2012 that are probably sitting in desk drawers around the Triangle. Be sure to check them for scratches or holes before using.

The new moon also occurs Thursday evening, at 5:56 p.m. to be exact. This is no coincidence. Solar eclipses can only occur at new moons (and lunar eclipses only at full moons), which makes perfect sense if you think about it. Solar eclipses are produced as the moon lines up between the Earth and the sun with the sun illuminating the far side out of our view.

If solar eclipses occur only when there is a moon and we have a new moon each month, then why isn’t there an eclipse each month? The answer comes in the moon’s orbit around the Earth which is tilted about 5º from the Earth’s orbit around the sun.

Most months, the shadow cast by the new moon misses the Earth. About every 18 months everything lines up showing a total eclipse somewhere on Earth. That somewhere is highly variable though.

For example, Los Angeles last saw a total eclipse in 1724 and won't see another until 3290. We only have to wait 2 years, 9 months, 29 days for the total eclipse of Aug. 21, 2017, where totality will be visible not far from our area.