Great American Eclipse of 2017


The Great American Eclipse of 2017 will be the biggest astronomical event this year. On Aug. 21, the moon will pass directly between the Earth and Sun and cast its shadow onto Earth in a total eclipse of the Sun.

Since the sun is a disk and not a point, there are two parts of the moon’s shadow, the penumbra, where only part of the sun is blocked and the umbra, where the entire Sun is blocked. The umbra is a cone of darkness extending 236, 000 miles from the moon into space. This is about 2,000 miles longer than the average Earth-moon distance, so the tip just barely touches the Earth when the alignments are right. Most months when the moon is in its “new” phase, roughly between the Earth and sun, this cone of darkness misses the Earth because the moon’s orbit is not in the same plane as Earth’s. Thus the shadow falls above or below the Earth. About twice a year, though, the new moon is in the same plane as the Earth and sun, allowing the shadow to fall on the Earth, treating Earthlings to a solar eclipse.

On Aug. 21 this year, the cone of the moon’s umbra will contact the surface of Earth at sunrise (12:48:45 pm Eastern Daylight Time, EDT) northwest of the Hawaiian Islands. At 10:15:50 a.m. Pacific Daylight Time (1:15:50 p.m. EDT), the umbra will sweep onto the Oregon coast, just north of Newport. A swath of total darkness about 100 miles wide and lasting about two minutes for those in its center, it will race eastward at almost 3,000 mph across the United States as shown in Figure 1. Gradually slowing to 1,500 mph and spreading to 115 miles wide, it will leave Cape Island in South Carolina’s Cape Romain Wildlife Refuge at 2:49:07 p.m .EDT. At sunset a few hundred miles south of the Cape Verde Islands the moon’s umbra will leave the surface of Earth at 3:03 p.m. EDT to again extend, unnoticed, into the darkness of space until July 2, 2019 when it will again cross the Earth, this time in the Pacific Ocean and South America. A video of the Moon’s shadow crossing Earth is available at

For the hour and 34 minutes it takes the shadow to cross the United States, including a number of major cities, millions of Americans will experience what I am told is the most magnificent of cosmic experiences, a total eclipse of the Sun. Unfortunately, I have never had the privilege to view this, though the current chair of the Adirondack Public Observatory’s Board of Trustees has seen a number of them. I should be able to see this one as I have been invited to Atchison, Kansas for the event where we will experience about 2 minutes and 20 seconds of totality.

As well as those lucky enough to experience the total eclipse, everyone in North America will be able to view a partial eclipse of the Sun (the view from the penumbra). In Tupper Lake, the moon will begin to cover the sun at 1:21 p.m. and block 62.6 percent of it at 2:38:56 p.m. as shown in Figure 2. This will dim the sun so little, some people won’t even know it’s happening. For the attentive, the darkness will be much like that of a passing cloud, but the “bite” out of the disk of the sun as seen through eclipse glasses will be very obvious. The partial eclipse will end in Tupper Lake at 3:53 p.m.


Yes, you can view the eclipse with eclipse glasses that will be available at the Adirondack Public Observatory’s Tupper Lake office at 36 High St. and the Roll-Off Roof Observatory above Little Wolf Pond during Friday night observing sessions and on the day of the eclipse. They are also available with free shipping and bulk discounts at, a website created by astronomers for this event. There has been a great deal of frightful misinformation about solar eclipses that has prevented people from viewing and allowing children to view these fascinating events. The sun is no more dangerous during an eclipse than it is normally. But normally, it’s too painful to look at long enough to harm our eyes. During an eclipse, when it is dimmer, it’s easier to stare at, so that’s the danger. Eclipse glasses are certified to filter the sun’s harmful UV radiation and allow safe viewing of the disk of the Sun.

Another way to view the eclipse is to use a pin-hole camera. Simply put a tiny hole in an index card and allow the sun to shine through the hole onto another index card, wall or the ground. In the dappled shadows under leafy trees, the usually round spots will be crescent suns since the gaps between the leaves act as natural pinhole cameras. A colander held in the sunlight will produce the same effect in its shadow!

There will be many organized viewing opportunities all over North America. If you are on the continent, you will be able to see the eclipse, barring clouds. There are many resources on the internet. I recommend you start at or www. where you can access information about the eclipse circumstances wherever you may be as well as learning how to observe it safely. Another resource is We astronomers want everyone to observe this amazing cosmic alignment.

Don’t fret too much if you can’t get to the path of totality this year because the Adirondacks will be in the path of totality on April 8, 2024! In Tupper Lake will be able to experience totality from 3:24:25 p.m. to 3:27:57 p.m. … 3 minutes and 31 seconds of darkness at mid-afternoon! So observe this year’s eclipse as practice and start looking forward to 2024.

The astronomers of the Adirondack Public observatory will be happy to share the wonders of the night sky and the eclipse of August 21 from our RORO above Little Wolf Pond in Tupper Lake. We’re open to the public on the first and third Fridays of each month, weather permitting. For updates and notices, check out our website at and our Facebook page. On our public observing days you can also call the RORO at 518-359-6317 to talk with one of our astronomers. Observing starts about one half hour past sunset.