Podcaster: Jay Pasachoff
Title: Partial Solar Eclipse October 23, 2014
Organization: Williams College and Caltech
Links: http://www.eclipses.info and http://www.totalsolareclipse.org
Description: Preparation for the partial solar eclipse in the western United States on October 23 in the afternoon.
Bio: Jay Pasachoff, Chair of the International Astronomical Union’s Working Group on Eclipses, is Field Memorial Professor of Astronomy at Williams College and a Visitor at Caltech. He has viewed 64 solar eclipses, and is an expert on both their use for scientific observations and their use for public education. Pasachoff is a former president of the International Astronomical Union’s Commission on Education and Development and Chair of the Historical Astronomy Division of the American Astronomical Society. He received the Education Prize of the American Astronomical Society, the Janssen Prize of the Société Astronomique de France, and this year’s Richtmyer Memorial Lecture Award from the American Association of Physics Teachers. Pasachoff is the author or co-author of The Cosmos: Astronomy in the New Millennium, the Peterson Field Guide to the Stars and Planets, and Nearest Star: The Surprising Science of Our Sun plus, on a more technical level, The Solar Corona, as well as a new, 2017 book, The Sun, for the Science Museum, London.
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Transcript:
This piece is scheduled to appear on October 21st 2014, two days before a partial eclipse of the sun will be visible in the whole United States except for the easternmost part of the Eastern Seaboard. Usually, there is a total eclipse of the sun about every 18 months and an annular eclipse of the sun, when the moon isn’t quite big enough to cover the sun across the center, also about every 18 months. The year 2014 is unusual in that there is no total or annular eclipse but there are a couple of partial eclipses: the first one was back in April and the second is on October 23rd.
In the afternoon of October 23rd, the eclipse will be about 60% coverage of the sun by the moon through Oregon and Washington, ranging down to about 45% in Southern California. There will be a meeting of professional/amateur eclipse enthusiasts at the Sacramento Peak Observatory of Sunspot, New Mexico, in the days following the eclipse. We will all be observing the eclipse from that 9200-ft altitude on the afternoon of October 23rd.
This eclipse will be good practice also for observing the eclipse of August 21st, 2017, in which a path of totality will cross the continental United States from upper left to lower right, that is, Oregon to South Carolina. That path is only 100-km-or-so wide, so most people will have just a partial eclipse. And the partial eclipse could be 80%, 90% etc. But whenever any little sliver of the everyday sunlight, which is the photosphere, appears it is too bright to look at safely, so the precautions that one has to take to observe a partial eclipse of the sun are the same for this October 23rd, 2014, eclipse as they will be for everybody outside the path of totality on August 21st, 2017, and also for the people even in the path of totality before and after the couple minutes of totality.
In order to observe the sun safely on any day, including today, you need to cut down the sun’s intensity by a factor of between 100,000 and 1,000,000; that is, neutral-density 5, because of the five zeros, and neutral-density 6, because of the six zeros. That can be done with a readily available welding filter of at least shade 12, which is more commonly available than the more desirable shade of 14.
There are a lot of possibilities of getting some aluminized mylar that is made to safe specifications. Companies like Rainbow Symphony and Thousand Oaks Optical sell these filters for 50 cents or a dollar apiece. But between when you read this on the 21st, you’re not going to be able to get one on the 23rd. Still, it would be a good notification for you to be prepared for the eclipse of 2017, for when many of us are trying to arrange for such filters to be more widely available locally for people.
We know there are stories of misguided individuals saying that eclipses are too hazardous to look at all or that you should see them on TV or that you’ll go blind. And we think it is important for people to have correct information. In fact, eclipses can be very inspiring, especially to students, who may be really interested in seeing the sky go pretty dark at the time of the eclipse; this will happen in 2017, but it won’t happen in this year’s partial eclipse. So students should be encouraged to see the eclipse but to see the eclipse safely. For an eclipse like this one, where the moon half-covers the sun for the peak of the eclipse, you can just use the idea of a pinhole camera, where a punched hole on a piece of paper or cardboard projects an image few feet away. And under a tree, you might naturally get a lot of little pinhole images of partially eclipsed sun on the ground or on the wall on an angle. (It might appear often on a wall in the western United States because the eclipse will be low in the sky in the afternoon of October 23rd.)
During the total eclipse that will be visible for 2 minutes in that narrow 100-km-wide band in 2017, then you can and should watch without any eye protection because then the everyday sun is covered and only the solar corona will be visible, which would be exciting to see and it is about the same brightness as the full moon and equally safe to look at. But again, before that and after that and off to the sides for a partial eclipse like this one, and for an ordinary day like any other day that the sun is shining, you do need some protection if you are going to look up at the sun or you should project the sun down on the ground and stand with your back to the sun and look at the projection. One can use binoculars, for example, also to project down on the ground, but you must be very careful not to look at the sun through to the binoculars. Use it only to project away from you and stand with the sun on your back if you are using binoculars.
Eclipses are fun to see. The next total eclipse will be in Svalbard in the Arctic north of Norway on March 20th in 2015. The year after, there will be an eclipse site that goes across Indonesia on March 9th of 2016. And then little more than a year later will come the Great American eclipse of August 21st, 2017; in fact, there is a website by Michael Zeiler called GreatAmericanEclipse.com that has a lot of maps and information about where to go and what to see in 2017.
On behalf of the Working Group on Eclipses of the International Astronomical Union, I run a website at the easy-to-remember address of eclipses.info. So just type “eclipses.info” into your web browser and you can see links to maps by several people who have automated the maps so that you can click on the Google map to see the local circumstances and times and angles for your particular location. Increasingly there are several different kinds of maps that are available for eclipses, including some by Fred Espenak, who has an eclipse site at eclipsewise.com, taking over from his former NASA eclipse site. There are maps from Michael Zeiler, a professional mapmaker who is now applying his skills to eclipse maps. And from Xavier Jubier, a French information technology specialist who has put these Google maps online with the path of totality or of the limits of the partial eclipse on them. Also, the meteorologist Jay Anderson, with whom I have just submitted to Houghton Mifflin Harcourt the Peterson Field Guild to Weather, has a website at eclipser.ca, (that’s in Canada). So, eclipser.ca. And his website has his calculations of cloud statistics from satellites over about 25 years and also some tables based on ground-based observations on cloudiness for 25 years. So, particularly for the 2017 eclipse, you can look at that website and evaluate where the average cloudiness on that day of August is likely to be least. It turns out that the western sites are on the whole better than the eastern sites on that occasion.
I wish you happy observing of eclipses both these partial possibilities and eventually the Great American Eclipse of August 21st, 2017. This is Jay Pasachoff talking.
End of podcast:
365 Days of Astronomy
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