When the total solar eclipse traces a path across Mexico, the United States and Canada on April 8, spectators can anticipate a multitude of awe-inspiring moments. <\/p>\n
During a total solar eclipse, the moon completely blocks the face of the sun for a brief period known as totality \u2014 and 32 million people in the US who are located along the 115-mile-wide (185-kilometer-wide) path of totality for April\u2019s event will have a chance to enjoy this full expression of the celestial spectacle. <\/p>\n
It\u2019s worth taking some time to stop and take in this historic celestial event because a total solar eclipse won\u2019t be visible across the contiguous US again until August 2044 and an annular eclipse, in which the moon can\u2019t completely block the sun, won\u2019t appear across this part of the world again until 2046. <\/p>\n
\u201cUntil you\u2019ve actually seen (a total eclipse), it\u2019s almost impossible to describe,\u201d said Dr. John Mulchaey, Carnegie Institution for Science\u2019s deputy for science and the director and Crawford H. Greenewalt Chair of the Carnegie Observatories. \u201cWhen you see totality, you can see how it\u2019s had such a huge impact on humans through thousands of years. It\u2019s one of the most beautiful things most people will ever experience.\u201d <\/p>\n
But the phases surrounding totality \u2014 including a couple phenomena stunning enough to have earned their own names \u2014 are pretty memorable, too, eclipse experts say. Here\u2019s what to look out for. <\/p>\n
The moon doesn\u2019t suddenly appear between Earth and the sun \u2014 the event begins with a partial eclipse, in which the moon appears to take a \u201cbite\u201d out of the sun. Depending on your location, the partial eclipse can last between 70 and 80 minutes, according to NASA. <\/p>\n
For those living outside of the path of totality, a crescent-shaped partial eclipse, rather than a total eclipse, will be the main event. <\/p>\n
Within the path, the partial eclipse is the longest phase, but as the time for totality nears, look for changes in the sky\u2019s appearance. <\/p>\n
\u201cAbout 15 to 20 minutes before totality, the sky starts getting this really weird gloomy color,\u201d Mulchaey said. \u201cIt\u2019s almost like a gray because the sun\u2019s way high in the sky, but it\u2019s almost entirely blocked out. It\u2019s not like twilight, sunset or sunrise when (the sun is) low in the sky. It\u2019s above you. And all of a sudden, you\u2019re losing most of the sun\u2019s light, and it feels very weird.\u201d <\/p>\n
The eerily darkening sky is a cue for skywatchers that the stellar show is about to begin. Just make sure you have eclipse glasses handy to safely view the sun before the event gets underway. <\/p>\n
Two breathtaking phases occur within the final moments before totality, Mulchaey said. <\/p>\n
When the moon begins to cross in front of the sun, the star\u2019s rays will shine around valleys on the moon\u2019s horizon, creating glowing drops of light around the moon called Baily\u2019s beads. The phenomenon was named for English astronomer Francis Baily, who noted them during an annular eclipse on May 15, 1836. <\/p>\n
As totality nears, Baily\u2019s beads will quickly disappear and make way for the \u201cdiamond ring,\u201d a nickname for how it looks when a single point of light remains \u2014 like a glistening giant diamond ring. <\/p>\n
Both of these phases last less than a minute, Mulchaey said. <\/p>\n
Then, it\u2019s time for totality. <\/p>\n
The totality phase of the April 8 eclipse is expected to last twice as long as it did in 2017 because the moon is currently closer to the sun. Those squarely along the center line of the path will see a total eclipse that lasts between 3\u00bd and 4 minutes, according to NASA. <\/p>\n
\u201cAll of a sudden, totality happens, and the corona shows up,\u201d Mulchaey said. \u201cEven though it\u2019s dark out, it\u2019s somehow glorious.\u201d <\/p>\n
The corona is the sun\u2019s ultrahot outer atmosphere, which emits a glow that can be seen around the moon during the eclipse. Typically, the corona is hard to see because the sun\u2019s surface is so much brighter. During the total eclipse, the corona will resemble white streams of light, according to NASA. <\/p>\n
During the 2017 eclipse, the sun was approaching solar minimum, or the quiet phase of our star\u2019s 11-year activity cycle. Now, the sun is nearing solar maximum, when the sun is exceptionally active, Mulchaey said. The corona will likely appear brighter and fuller, and there may be a chance to spot flaring loops of solar activity resembling streamers within the corona during the eclipse. <\/p>\n
Spectators may also be able to see a region of the solar atmosphere called the chromosphere, which will appear as a thin, pink circle around the moon. <\/p>\n
Bright stars or planets like Venus may shine in the dark sky, and the air temperature will drop as the sun disappears. The sudden darkness also causes animals to behave in unusual ways. <\/p>\n
\u201cWe may start to see nocturnal behavior, like crickets chirping or bats emerging, and animals stopping daytime behaviors, like birds going to roost or flying insects landing,\u201d said Dr. Andrew Farnsworth, visiting scientist at the Cornell Lab of Ornithology. <\/p>\n
After totality ends, the diamond ring and Baily\u2019s beads will briefly reappear before the partial eclipse returns as the moon slowly moves across the sun. <\/p>\n
It has only been six years since a total eclipse crossed the US, the path of the April 8 eclipse is a very different one, trekking from west to east. <\/p>\n
On average, an eclipse occurs in the same place every 375 years, Mulchaey said. <\/p>\n
And we\u2019re living at the right time to truly enjoy the sight of a total eclipse on Earth, he said. <\/p>\n