How to plan for this year's once-in-a-century solar eclipse - KVOA | KVOA.com | Tucson, Arizona

How to plan for this year's once-in-a-century solar eclipse

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It is not too early to begin preparing for the Great American Solar Eclipse of Aug. 21, 2017 — and the sun's position on April 19, 20 and 21, but especially April 20, will offer a perfect dress rehearsal for that historic event.

When preparing for the eclipse, an important aspect to consider is the sun's location in the sky for your location. Across the western third of the United States, the eclipse will reach its peak during the late morning hours. Over the nation's midsection, the maximum eclipse will come at midday, and for the eastern third of the country, the time of greatest coverage of the sun by the moon will happen in early to mid-afternoon.

Will tall trees or nearby buildings block your view of the sun at the critical moment? You can get a very good idea of where the sun will be in the sky during the eclipse by noting its position on April 19, 20 and 21.

During these three days, the sun will track across the sky along a path that will be very similar to the path it will take on the actual eclipse day, Aug. 21. In fact, the path that the sun will take on Friday, April 21 will virtually match its track on the day of the eclipse. The declination of the sun — its angular distance north of the celestial equator — will be equal to 11.73 degrees on April 20, compared to 11.87 degrees on Aug. 21, a difference of just 0.14 of a degree.

On April 20, the sun will be less than a half degree (equal to its apparent width) to the south of its path on eclipse day, while on April 21, it will be a similar distance to the north of its Aug. 21 position.

The only other significant difference is that the sun will arrive at its eclipse-day position about 4 minutes earlier on the three April dates compared to Aug. 21. The reason for this difference is related to what is known as the "equation of time," which is a way of quantifying the variable part of the difference between time kept by an ordinary electrical or mechanical clock and the time kept by the sun, such as what a sundial would read.

Put in simple terms, in late April, the sun appears to cross the meridian about 4 minutes earlier than it does in late August.

Click here to see 20 selected cities, including Tucson, where viewing may be maximized.

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