Frequently asked questions about solar eclipses
Folks who are curous about solar eciipses have lots of questions about them. We attempt to provide answers to the most frequently asked questions. Of course we do not answer every question you may have, so feel free to post comments with your own burning questions about one of nature's most fanasitic astronomical phenomena.
1. What causes a solar eclipse?
A solar eclipse occurs when the moon passes directly between the sun and any portion of the surface of the earth. When that alignment occurs, the moon's shadow intersects the earth, and an eclipse occurs at those locations within the earth's shadow.
When the moon is between the earth and the sun, the moon is in its "new moon" phase. Accordingly, the illuminated portion of the moon faces away from the earth, and the moon itself is not visible in the sky. For that reason, as the moon passes in front of the sun, it will appear as though an unseen animal has taken a dark bite out of the sun's disk. The bite may include a portion of the sun (partial eclipse), up to the entire visible disk of the sun. When the moon blocks the entire disk of the sun from view at one particular location on earth, the resulting eclipse is a total eclipse.
The image above shows the alignment of the sun, moon and earth during a total solar eclipse. The moon casts a dark shadow, the umbra on the earth as well as a less dark shadow (the penumbra). In the areas where the umbra touches the earth's surface, viewers can see a total eclipse. By contrast, in the areas where the penumbral shadow touches the earth, only a partial eclipse is visible.
2. Why don’t we have a solar eclipse every month?
The moon passes between the sun and the earth every 29.53 days, on average. As a result, there is a new moon every month, and in some cases, there may be two new moons within one calendar month. On the other hand, solar eclipses are far rarer than are new moons, with solar eclipses occurring once or twice about every 6 months. Total solar eclipses are even rarer and occur only once every 18 months or so.
The moon's orbit is inclined from the plane of the earth's orbit by about 5 degrees. Because of this inclination, when the moon passes between the earth and the sun during a new moon phase, the moon can be well above or below the plane of the earth. In these two out-of-plane alignments, the shadow of the moon may completely or partially miss the surface of the earth. If the umbral shadow misses the earth the result is a partial eclipse in those locations where the penumbral shadow reaches the earth. If the penumbral shadow misses the earth, there will be no partial or total eclipse anywhere on earth. These misalignments are more frequent than the perfect alignment shown in the above figure. For that reason, most new moons do not produce eclipses.
A detailed explanation with an accompanying animation showing why eclipses occur with the frequency that they do can be founnd here.
3. What will I see during a solar eclipse?
4. Can I take an eclipse photo with my smart phone?
A search of the internet will turn up conflicting answers to this question. Many sources insist that taking pictures of the sun can damage a smartphone camera. An article in the USA today quotes Apple as saying that taking a picture of the sun with an iPhone will not hurt your camera. According to Apple, most smartphone cameras take wide-angle pictures in which the sun is a relatively small part of the picture and even normal sunlight should not damage a smartphone camera.
No portion of an eclipse supplies more sunlight light than does any daylight picture of the sky. Accordingly, you probably can take eclipse pictures with your smartphone. Additionally, if you are either wearing protective eyewear or are taking pictures during totality, you won't hurt your eyes either.
On the other hand, you won't take great photos with your smartphone camera. Your photos will look like the shot on the left rather than the one on the right. And let's be honest. Your plan is to take pictures more like the one on the right that was taken by NASA photographer Aubrey Gemignani.
Nevertheless, you will want that smartphone picture. Additionally, you will want pictures of your family and friends doing all that fun stuff that you told them that the trip was really about (wink). You will also want pictures of your real eclipse-taking camera set up, and obviously, you cannot take pictures of that with the eclipse camera. Your smartphone will also have a GPS, and it will have that Eclipse Planner app that will let you know that you have arrived at the perfect place to view and photograph the eclipse.
5. What is the Great American Eclipse of 2024?
The Great American Eclipse is a name given to the eclipse occurring on April 8, 2024. The term also applies to the August 21, 2017 eclipse. "Great American Eclipse" refers to the fact that the landed path of totality of each of these eclipses is primarily or entirely within the North American continent.
The span of the April 2024 eclipse is as follows:
First, after the eclipse begins in the South Pacific Ocean, the path of totality of the eclipse makes landfall near Mazatlán on the Western coast of Mexico. Secondly, upon leaving Mexico, the path of totality traverses the North American continent in a northeasterly direction, passing through 14 states in the United States before exiting the United States entering Canada. Finally, upon exiting mainland Canada at the east coast, the path of totality continues westward over the island of Newfoundland and then into the North Atlantic ocean. The total eclipse ends well well before its path of totality reaches Europe. For an interactive map of the path of totality for the April 2024 eclipse, please start here Path of Totality: April 8, 2024, Total Solar Eclipse
The next Great American total eclipse will be the total solar eclipse of August 12, 2045. In contrast, the eclipse of October 14, 2023, also spans the North American continent; however, the 2023 eclipse is an annular ("Ring of Fire) eclipse.
For more information about eclipses over the North American continent, past or future see The Great North American Eclipses.
6. What large cities are in the path of totality of the 2024 Great American Eclipse?
The path of totality of the Great American Eclipse of 2017 missed most of the largest cities in the United States. The largest city along the path of totality was Nashville TN. By contrast, the Great American Eclipse of 2024 will pass through a number of large cities in three countries; Mexico, the United States, and Canada.
Mexico
The largest Mexican cities along the path of totality are Torreon, Durango City, Mazatlan, and Piedras Negras. Torreon is the largest such city.
United States
The 2024 total eclipse passes by several large United States cities, with the largest being Dallas. In addition, the eclipse also passes through Indianapolis, Cleveland, and Buffalo. The best calculations indicate that the path of totality will narrowly miss San Antonio Texas.
Canada
Finally, the path of the eclipse also narrowly misses Toronto. Montreal is the largest city in Canada within the path of totality for the 2024 Eclipse. On the other hand, nearly the entire population of the United States, Canada, and Mexico will be able to see at least a partial eclipse. The exceptions include the most northwestern portions of Canada and all but the eastern portions of Alaska.