Eclipse: Who? What? Where? When? and How?
Total Solar Eclipse
On Monday, August 21, 2017, all of North America will be treated to an eclipse of the sun. Anyone within the path of totalitycan see one of nature’s most awe-inspiring sights – a total solar eclipse. This path, where the moon will completely cover the sun and the sun’s tenuous atmosphere – the corona – can be seen, will stretch from Lincoln Beach, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun’s disk.
Image Credit: Rick Fienberg, TravelQuest International and Wilderness Travel
Figure 1- In this series of still from 2013, the eclipse sequence runs from right to left. The center image shows totality; on either side are the 2nd contact (right) and 3rd contact (left diamond rings that mark the beginning and end of totality respectively).
Who Can See It?
Lots of people! Everyone in the contiguous United States, in fact, everyone in North America plus parts of South America, Africa, and Europe will see at least a partial solar eclipse, while the thin path of totality will pass through portions of 14 states.
Image Credit: NASA’s Scientific Visualization Studio
Figure 2- This map shows the globe view of the path of totality for the August 21, 2017 total solar eclipse. You can find more information at: https://svs.gsfc.nasa.gov/4518(link is external) (link is external)
What is It?
This celestial event is a solar eclipse in which the moon passes between the sun and Earth and blocks all or part of the sun for up to about three hours, from beginning to end, as viewed from a given location. For this eclipse, the longest period when the moon completely blocks the sun from any given location along the path will be about two minutes and 40 seconds. The last time the contiguous U.S. saw a total eclipse was in 1979.
Figure 3 – Diagram showing the Earth-sun-moon geometry of a total solar eclipse. Not to scale: If drawn to scale, the Moon would be 30 Earth diameters away. The sun would be 400 times that distance.
Where Can You See It?
You can see a partial eclipse, where the moon covers only a part of the sun, anywhere in North America (see “Who can see it?”). To see a total eclipse, where the moon fully covers the sun for a short few minutes, you must be in the path of totality. The path of totality is a relatively thin ribbon, around 70 miles wide, that will cross the U.S. from West to East. The first point of contact will be at Lincoln Beach, Oregon at 9:05 a.m. PDT. Totality begins there at 10:16 a.m. PDT. Over the next hour and a half, it will cross through Oregon, Idaho, Wyoming, Montana, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, and North and South Carolina. The total eclipse will end near Charleston, South Carolina at 2:48 p.m. EDT. From there the lunar shadow leaves the United States at 4:09 EDT. Its longest duration will be near Carbondale, Illinois, where the sun will be completely covered for two minutes and 40 seconds.
Figure 4 – A map of the United States showing the path of totality for the August 21, 2017 total solar eclipse.
When Can You See It?
Times for partial and total phases of the eclipse vary depending on your location. This interactive eclipse map(link is external) will show you times for the partial and total eclipse anywhere in the world.
How Can You See It?
You never want to look directly at the sun without appropriate protection except during totality. That could severely hurt your eyes. However, there are many ways to safely view an eclipse of the sun including direct viewing – which requires some type of filtering device and indirect viewing where you project an image of the sun onto a screen. Both methods should produce clear images of the partial phase of an eclipse.
Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”), when the moon entirely blocks the sun’s bright face, which will happen only within the narrow path of totality (https://go.nasa.gov/2pC0lhe(link is external)).
The only safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses” (example shown at left) or hand-held solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the sun; they transmit thousands of times too much sunlight. Refer to the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers(link is external) page for a list of manufacturers and authorized dealers of eclipse glasses and handheld solar viewers verified to be compliant with the ISO 12312-2 international safety standard for such products.
- Always inspect your solar filter before use; if scratched or damaged, discard it. Read and follow any instructions printed on or packaged with the filter.
- Always supervise children using solar filters.
- Stand still and cover your eyes with your eclipse glasses or solar viewer before looking up at the bright sun. After looking at the sun, turn away and remove your filter — do not remove it while looking at the sun.
- Do not look at the uneclipsed or partially eclipsed sun through an unfiltered camera, telescope, binoculars, or other optical device.
- Similarly, do not look at the sun through a camera, a telescope, binoculars, or any other optical device while using your eclipse glasses or hand-held solar viewer — the concentrated solar rays will damage the filter and enter your eye(s), causing serious injury.
- Seek expert advice from an astronomer before using a solar filter with a camera, a telescope, binoculars, or any other optical device. Note that solar filters must be attached to the front of any telescope, binoculars, camera lens, or other optics.
- If you are within the path of totality (https://go.nasa.gov/2pC0lhe(link is external)), remove your solar filter only when the moon completely covers the sun’s bright face and it suddenly gets quite dark. Experience totality, then, as soon as the bright sun begins to reappear, replace your solar viewer to look at the remaining partial phases.
- Outside the path of totality, you must always use a safe solar filter to view the sun directly.
- If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them, or hold your handheld viewer in front of them.
Note: If your eclipse glasses or viewers are compliant with the ISO 12312-2 safety standard, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren’t scratched, punctured, or torn, you may reuse them indefinitely. Some glasses/viewers are printed with warnings stating that you shouldn’t look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 standard adopted in 2015. To make sure you get (or got) your eclipse glasses/viewers from a supplier of ISO-compliant products, see the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers(link is external) page.
An alternative method for safe viewing of the partially eclipsed sun is pinhole projection(link is external). For example, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a waffle pattern. With your back to the sun, look at your hands’ shadow on the ground. The little spaces between your fingers will project a grid of small images on the ground, showing the sun as a crescent during the partial phases of the eclipse. Or just look at the shadow of a leafy tree during the partial eclipse; you’ll see the ground dappled with crescent Suns projected by the tiny spaces between the leaves.
Figure 5 – Check with local science museums, schools and astronomy clubs for eclipse glasses—or purchase an ISO 12312-2 compliant pair of these special shades!
Figure 6 – This list describes when to wear your glasses and when you can safely look at the eclipse, only during totality!
Image Credit: NASA Kepler Mission
Using a projection method to view the sun.
Image Credit: NASA Jet Propulsion Laboratory.
Credit : NASA