On Aug. 21, North America will be treated to a spectacular sight: a solar eclipse. People along a 70-mile swath of the mainland from Lincoln City, Oregon, to Charleston, South Carolina, will spend two to three minutes in the dark as the moon totally covers the sun.
But why does this happen, what will we see on the Big Island and is it really a big deal?
Solar eclipses occur when the moon is directly between the Earth and the sun. The sun is 400 times wider than the moon, but also 400 times farther away. As a result, the moon and the sun are the same size in our sky. Thus when moon is exactly between the earth and the sun, the moon completely blocks the sun from view. Astronomers call this a total solar eclipse. Total eclipses last two to 10 minutes in a given location.
At this point, you may be remembering elementary school science and wondering why we do not have an eclipse every month. The moon, sun and the planets orbit along the same plane in the solar system, called the ecliptic. We know the ecliptic by the constellations that mark it in the sky — the constellations of the Zodiac. The path of the sun and the moon are not perfectly aligned, the moon moves five degrees above and below the ecliptic. While the moon and sun appear to be the same size in our sky, their actual sizes are very different. For a solar eclipse to occur, the moon must be exactly between the earth and the sun, not a few degrees above or below.
A total eclipse is rare and only visible on a very small portion of the Earth’s surface, a path roughly 70 miles wide known as the path of totality. Many more people see a partial eclipse where the moon covers a portion of the sun. Right outside the path of totality, the moon may cover 99 percent of the sun, while areas farther away may see five to 10 percent of the sun covered. Other places in the world will see nothing special.
The Aug. 21 eclipse is a partial eclipse in Hawaii. About 20 percent of the sun will appear to be covered here on the Big Island. The maximum of the eclipse, the time when the full 20 percent will be covered, will be at 6:35 a.m., with the sun rising at 6:02 a.m.
While Hawaii is not the optimal location for viewing the eclipse, it is important to keep in mind eclipse safety. Our eyes are very sensitive to light and even the smallest amount of direct sunlight can cause damage to the eyes in a few seconds. The only way to safely view the eclipse directly is through the use of special filters, either in the form of eclipse glasses or specific telescope filters. Pinhole cameras or other projection methods allow you to safely view the eclipse by looking at the sun indirectly.
Total solar eclipses occur every year or two worldwide. For example, the next total solar eclipse will be in 2019 and will be visible in parts of Chile and Argentina. However, a total solar eclipse occurring in your location is a rare occurrence. The last total solar eclipse in Hawaii was July 11, 1991.
Another total eclipse will not be visible in Hawaii this century. Our next best eclipse, a partial eclipse, will be on Feb. 5, 2046, when 92 percent of the sun will be covered.
For more eclipse information, check out the Canada-France-Hawaii Telescope Facebook page. We will post links to eclipse viewing webcasts, eclipse photos and news throughout August.