A total solar eclipse will sweep across North America on Monday, giving millions of people the rare opportunity to see the afternoon sky temporarily darken as the moon blocks the face of the sun.
The eclipse's path happens to pass through Mexico, fifteen U.S. states and a small portion of eastern Canada. In all other states in the continental US, viewers will be treated to a partial solar eclipse, where the moon will appear to take a bite out of the sun and darken some of its light.
Here's everything you need to know about this rare celestial event.
What is a solar eclipse?
Solar eclipses occur when the sun, moon and Earth align. The moon passes between the Earth and the sun, temporarily blocking the sun's light and casting a shadow on the Earth.
A total solar eclipse occurs when the moon completely obscures the sun, while a partial solar eclipse only blocks part of the sun's face.
Solar eclipses only occur at the new moon. Because the moon's orbit is tilted around the Earth, the three bodies do not always lie on a line that causes an eclipse.
"Imagine if the moon's orbit were in the plane of the Earth's orbit around the sun - if that were the case, you would have a total solar eclipse with every new moon and a total solar eclipse with every full moon lunar eclipse," Neil DeGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, told NBC News. "So because things don't always line up, it adds to the rarity of the event and the special nature of the event."
Where and when will the solar eclipse be visible?
This year's solar eclipse will follow a slightly wider path over more populated areas of the continental US than other total solar eclipses in the recent past.
NASA estimates that 31.6 million people live within what is known as the path of totality, where the total solar eclipse will be visible. Another 150 million people live within 200 miles of the path, according to the agency.
The trail passes through Texas, Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine. Small parts of Michigan and Tennessee may also witness totality if conditions are clear.
After the eclipse moves into Canada, it will pass over southern Ontario, Quebec, New Brunswick, Prince Edward Island and Cape Breton, on the eastern side of Nova Scotia.
Those outside the path of totality can still participate in the astronomical event by watching a partial solar eclipse - visible in all 48 states of the contiguous U.S. - or a NASA livestream.
The timing, including how long totality lasts, depends on location, but in some spots the moon will completely cover the sun for up to 4 minutes and 28 seconds.
Below is a list of timings for some cities along the path of totality, as provided by NASA. A number of other resources, including NationalEclipse.com and TimeandDate.com, can also help people plan.
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Dallas: Partial solar eclipse begins at 12:23 PM CT and totality at 1:40 PM
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Little Rock, Arkansas: Partial solar eclipse begins at 12:33 PM CT and totality at 1:51 PM
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Cleveland: Partial solar eclipse begins at 1:59 PM ET and totality at 3:13 PM
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Buffalo, New York: Partial solar eclipse begins at 2:04 PM ET and totality at 3:18 PM
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Lancaster, New Hampshire: Partial solar eclipse begins at 2:16 PM ET and totality at 3:27 PM
How to watch a solar eclipse safely
It is never safe to look directly at the sun, even if it is partially or mostly covered by the moon. To view solar eclipses safely and prevent eye damage, special eclipse glasses or pinhole projectors are needed. Failure to take proper precautions can lead to serious eye damage, according to NASA.
Eclipse glasses are thousands of times darker than normal sunglasses and are specially made to allow wearers to look at the sun during these types of celestial events.
Sky watchers should also never view any part of the sun through binoculars, telescopes or camera lenses unless they have specific solar filters attached. Eclipse glasses should not be used with these devices as they do not provide adequate protection.
However, during the few minutes of totality when the moon completely blocks the sun, it is safe to view with the naked eye.
Beware of fake eclipse glasses. For legitimate pairs, the lenses must have a silver appearance on the front and black on the inside. The manufacturer's name and address must be clearly labeled and not torn or punctured. Also check that the ISO logo and code "IS 12312-2" are printed on the inside.
If you don't have eclipse glasses, you can make a homemade pinhole projector, which lets sunlight in through a small hole, focuses it, and projects it onto a piece of paper, a wall, or other surface to create an image of the sun. safe to watch.
All you need are two pieces of white cardboard or plain white paper, aluminum foil and a pin or thumbtack. Cut a 1- to 2-inch square or rectangle from the center of a piece of white paper or cardboard. Place aluminum foil over the cut-out shape and poke a small hole in the foil with a pin or drawing pin.
During the solar eclipse, place a second piece of white paper or cardboard on the ground as a screen and hold the projector with the foil facing up and your back to the sun. Adjusting how far you hold the projector from the second piece of paper changes the size of the image on the makeshift screen.
What to pay attention to while viewing the total solar eclipse
For those on the path of totality, there are some fun milestones to track as the total solar eclipse unfolds.
As the eclipse progresses and the sun gets thinner in the sky, Tyson says it will get eerily dark.
When the last rays of the sun are about to be eclipsed, watch for the "diamond ring effect": the sun's atmosphere will appear as an illuminated halo, and the last visible light will resemble the diamond of a giant ring.
As sunlight diminishes even further, the moon's rugged terrain will create an effect known as Baily's beads. Small "beads" of light will be visible around the dark moon for just a few seconds, as the last bits of sunlight peer through the moon's mountains and valleys.
When the moon completely blocks the sun, it is safe to take off the eclipse glasses and watch the total solar eclipse with the naked eye.
Some lucky sky watchers might even catch a glimpse of a comet.
Comet 12P/Pons-Brooks - nicknamed the 'devil's comet' because an outburst last year left behind two distinct trails of gas and ice in the shape of devil's horns - is currently visible from the Northern Hemisphere as it meanders through the inner solar system.
The comet can be seen early in the evening by staring at the west-northwest horizon. During the solar eclipse, when the sky darkens during totality, it may be possible to see the comet near Jupiter, but its visibility will depend on whether it is in the middle of an outburst and thus brighter than normal.
Most likely, all eyes will be on the alignment of the moon and sun.
"Most people won't even notice," Tyson said. "But if you know how to look, it's there."
When is the next solar eclipse?
The next total solar eclipse will occur in 2026, but will be largely over the Arctic Ocean, with some visibility in Greenland, Iceland, Portugal and northern Spain. In 2027, a total solar eclipse will be visible in Spain and part of North Africa.
The next total solar eclipse visible from North America will occur in 2033, but only over Alaska. In 2044, a total solar eclipse will cross Montana, North Dakota, South Dakota, parts of Canada and Greenland.
The next total solar eclipse that will cross the continental US from coast to coast will occur in 2045. The path of totality for that eclipse will cut through California, Nevada, Utah, Colorado, New Mexico, Oklahoma, Kansas, Texas, Arkansas, California, Nevada, Utah, Colorado, New Mexico, Oklahoma, Kansas, Texas, Arkansas, California, Nevada, Utah, Colorado, New Mexico, Oklahoma, Kansas, Texas and Arkansas run. Missouri, Mississippi, Louisiana, Alabama, Georgia and Florida.
This article was originally published on NBCNews.com
