Grand Traverse Astronomical Society

August 21, 2017 Total Solar Eclipse


Tips for viewing the August 21st Total Solar Eclipse

Last Chance to View a Total Solar Eclipse* until 2024

GTAS Links

Bob Moler's Links

NASA Links

Other Links

Tips for viewing the August 21st Total Solar Eclipse

By Bob Moler

* From the May 2017 issue of the GTAS newsletter Stellar Sentinel

What is a solar eclipse?

Solar eclipses or eclipses of the Sun occur in about one in six new moons. However one must be in the right part of the Earth to see them, which is why they may seem rare.

In a solar eclipse the moon’s shadow is cast upon the Earth. Because the Sun is a disk, the Moon’s shadow is fuzzy with sometimes a dark core. The fuzzy outer part of the shadow is called the penumbra. Observers there will see the Sun partially covered by the Moon, a partial eclipse. Observers in the dark core of the shadow are in the umbra, and see the face of the Sun completely covered by the Moon, a total eclipse. The maximum length of totality is never more than about seven minutes. Maximum for this eclipse will be 2 minutes 40 seconds. The maximum partial eclipse would be about 2 hours.

What is observed

The outer three layers of the Sun are potentially visible to us: photosphere, chromosphere, and corona. The photosphere is the bright ball of the Sun we normally see. Looking at it for any length of time will cause blindness. Never look at the Sun’s photosphere without an approved solar filter. The chromosphere is a thin red layer of gas above the photosphere. The other two layers can be seen during the totality of a solar eclipse. The chromosphere is a thin layer of gas just above the photosphere and can be seen in a Hydrogen Alpha solar telescope. The corona is a silvery white extended solar atmosphere that can be seen out to several solar radii out from the edge of the Moon eclipse Sun. It’s shape changes hour to hour.

Viewing the partial solar eclipse

Never look directly at the partially eclipsed Sun without an approved solar filter. Solar filters must comply with ISO 12312-2 and transmit no more than 0.0032% of sunlight, and preferably less. Items sold as Eclipse viewing glasses must state that they comply with ISO 12312-2. People like me who wear glasses will find gaps above and below the frames of these filters where the Sun can get in, so must be used with extreme caution. No eclipse is worth your eyesight. The damage caused by looking directly at the Sun may not be known for several days after exposure, then it’s too late.

I never use these filters, and prefer to project the Sun’s image on a white screen. I’ll have more on that next month.

Local eclipse times

Traverse City Open Space

Starts 12:58 p.m.

Maximum 2:20 p.m. 75.11% covered

Ends 3:40 p.m.

Sleeping Bear Dunes Dechow Farm on M22 about 4 miles north of Glan Arbor

Starts 12:57 p.m.

Maximum 2:19 p.m. 75.26% covered

Ends 3:39 p.m.

NASA provides an interactive map of the August 21, 2017 eclipse on the internet to allow the display of eclipse times for any location:

See Viewing the total solar eclipse in part 2 next month (June 2017) along with Sun projection methods

We will also be discussing it at this month’s meeting. If you plan on traveling to the path of totality please don’t miss this meeting.

Last Chance to View a Total Solar Eclipse* until 2024

By Bob Moler

* If you don’t want to travel outside of the continental United States.

Article from the August 2017 issue of the GTAS newsletter Stellar Sentinel

Warning: Viewing totality can be habit forming.

We have given you plenty of information and warnings with programs, Stellar Sentinel Articles, and web page links on our website But for many eclipse fever is now taking hold, so it’s a last time to reiterate the information for viewing the partial and total phases of a solar eclipse.

Going for Totality

The path that the Moon’s umbral shadow will take across the United States is at most about 90 miles wide, and the duration of totality will be from 2 minutes in Oregon to 2 minutes 40 seconds at the most in Kentucky, down to 2 minutes 35 seconds in South Carolina. That is the duration at the central line of the path. The duration of totality doesn’t change much if you are near the central line, but diminishes rapidly near the edge. So if you are within 5-10 miles of the central line of the path of totality, you’ll pretty much get the maximum effect.

Getting hotel accommodations anywhere near that path will be impossible, assuming you could afford it, which you can’t. At least I can’t. Accommodations can be found, hopefully, 2-300 miles away from the path of totality.

Mobility and timing is the key. I’d like to have a big old Bermuda high over the eastern United States, hot, clear, though somewhat hazy. But the way this year is going with lots of storms, I’ve not much hope for that. The weather last year was clear in the western states and cloudy in the eastern ones. There’s no guarantee that that will be the same this year.

Check forecasts from several sources. I have links to AccuWeather, The Weather Channel, and the National Weather Service apps on my smartphone. Most have interactive weather maps that can show a layer showing clouds taken by satellite. There’s a nice color coded satellite map provided by NOAA, the National Oceanic, and Atmospheric Administration. The GOES East satellite will show cloud cover in the infrared, so it will show clouds day or night at NOAA also has this eclipse 2017 website: It has statistical information about cloudiness statistics for August 21st, during the eclipse time for all parts of the nation.

Viewing the partial eclipse

Most of a solar eclipse, if you are in the path of totality or the entirety of the partial eclipse, part of the Sun’s brilliant photosphere will be exposed. The surface brightness of the partially eclipsed Sun is basically as bright and the uneclipsed Sun on your retina, since it is imaging the Sun, so it has the same inherent danger to your eyes, no more and no less than the uneclipsed Sun.

Projecting the Sun’s image is the safest way to view the partial eclipse. In my four total eclipses, I’ve made it a point, especially before totality to never look anywhere near the Sun, and to wear sun glasses as long as possible before totality so as to not affect my vision, or put any retinal fatigue spots in my vision from looking at too bright an object, even the projected Sun’s image too long.

Projection by pinhole is an easy way to view the Sun. Especially when the pinhole is the size as a paper punch hole and taped to a mirror, and the image is directed to the shady side of a building 10 or more feet away. Someone suggested bringing a colander and projecting a whole bunch of overlapping eclipsed suns with it. Or sit under a tree and let the tree act as a pinhole projector.

We’re expecting 100 cardboard eclipse glasses at the Sleeping Bear Dunes National Lakeshore’s Dechow/Klett farm for the event. They’ll go fast, But there will be better ways to view the eclipse there.

GTAS Links

The Great American Solar Eclipse August 21, 2017 and How to View it Safely

Slides from the the May 5, 2017 presentation to the Grand Traverse Astronomical Society.

Notes from the the May 5, 2017 presentation to the Grand Traverse Astronomical Society.

Bob Moler's Links

My July 20, 2017 Wordpress post at one month and a day prior to the eclipse. It includes a description of my first eclipse:

Other programs:

NASA Links

Main NASA site for the 2017 August 21 eclipse.

NASA Eclipse Web Site: Total Solar Eclipse of 2017 August 21.

Total Solar Eclipse Interactive Map, based on Google Maps.

Learn all about the August 21, 201 7 total solar eclipse: when and where you can see it, viewing techniques and safety tips.

Find out which spacecraft, balloons and ground-based teams will observe the August 21, 2017 total solar eclipse.

Visit the NASA Science website to find celebrations, information and activities for researchers, citizen scientists, educators, teens and kids.

NASA's Eyes on the 2017 Eclipse is an interactive, 3-D simulation of the August 21, 2017 total eclipse.

NASA will host the Eclipse Megacast, which will provide unique broadcast coverage across multiple locations.

Experience the 2017 solar eclipse in many fun, creative and challenging ways, from family-friendly activities to sophisticated science projects. Explore activities and find out about public engagement happenings in your community.

Other Links (in no particular order)

Reputable Vendors of Solar Filters & Viewers from the American Astronomical Society:

National Oceanic and Atmospheric Administration (NOAA) Eclipse weather page Ready Set, Eclipse:

NOAA's GOES East nearly real-time satellite images:

American Astronomical Society eclipse website about filters:

Astronomical Society of the Pacific 2017 Solar Eclipse Resources:

Photographing Space: How to Photograph a Total Solar Eclipse:

Dan McGlaun's Site: (Veteran of 12 total solar eclipses) Lots of information and links:

Popular's link for the eclipse:

A web site published by Michael Zeiler and Polly White:

Sky and Telescope, the premier astronomy magazine has this link:

Climate and weather for the total solar eclipse by Jay Anderson and Jennifer West::

Fred Espanek produced much od NASA's eclipse information before he retired a few years ago. Here is his eclipse site:

National Eclipse web site:

A Google Earth overlay for the August 21, 2017 eclipse by Xavier M. Jubier: TSE_2017_08_21.kmz
His website with many files for other eclipses is here:

Updated August 13, 2017, including the location of the Sleeping Bear Dunes event