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Why are some eclipses longer than others?
The longest lunar eclipse of the 21st century arrives on July 27, with a total duration of 43 minutes on Africa, the Middle East, and Central Asia. Nearly 4 hours will go from the moment the Earth's shadow darkens the edge of the moon until the full moon returns, according to Earthsky.org
For Comparison , the next lunar eclipse visible from North America, Jan. 21, 2019, will last just an hour and 2 minutes. According to NASA, the solar eclipse that swept through 14 US states in August 2017 remained in full for more than 2 minutes and 40 seconds.
What is the reason for these huge disparities between eclipses?
Solar eclipses – when the moon prevents sunlight from reaching Earth – it is still much shorter than lunar eclipses, when our planet moves between the sun and the moon. Kaisa Young, an astronomer at Nicholls State University in Louisiana, says, "If we think about it from an outside point of view, a solar eclipse is a small moon that casts a small shadow on a big planet." , did she say. "A lunar eclipse is a great planet casting a large shadow on a small moon."
When the moon blocks the sun's shadow of the Earth, as during a solar eclipse, the shadow – the complete shadow area, where the sun is totally blocked – is only a few tens of kilometers wide and zips across the planet. But the Earth's shadow is big, and the moon can take a long time to cross it – especially if it moves in the middle of the shadow, rather than bypassing the edges, says- she.
different solar eclipses and different lunar eclipses, said Young. And that has everything to do with the different models and cycles that govern their behavior.
The Earth, the moon and the sun are not in perfect alignment, explained Young. The orbit of the moon has a tilt of about 5 degrees and does not cross the same plane as the Earth and the sun twice in each of its 27-day orbits. This is the basic model that governs each eclipse.
About twice every 11 months, these crossings are timed so that the Earth, the Moon and the Sun are all aligned with each other. Each of these alignments occurs once – with the Earth between the moon and the sun (lunar eclipse) – and once with the moon between the Earth and the sun (solar eclipse), Young says
C & # 39; why solar and lunar eclipses tend to arrive. she added.
But not all alignments are created equal, because this 11-month cycle is not totally regular and stable. . Sometimes the alignment is imperfect, she says, and a shadow barely crosses a part of the Earth or the Moon. This is what happened on July 13, when the partial solar eclipse of the lunar eclipse swept the southern edge of Australia and the waters close to the sea. Antarctica
On other occasions, the alignment is near and the moon passes in the middle. from the shadow of the Earth, where the shadow of the moon passes near the Earth's equator. These eclipses last a lot longer, says Young.
The last factor affecting the length of an eclipse, she says, is the time of year. In July, the Earth reaches the farthest point of its sun's orbit, and it seems the smallest in the sky compared to other times of the year. This means that the Earth and the Moon cast larger shadows, which take longer to move. The Earth reaches its closest point to the sun in January, so our star at home seems particularly tall in the sky at this time, and the shadows of eclipses are smaller.
That is why the longest eclipses take place in the summer. The hemisphere, and the shortest eclipses occur when it is winter in the northern hemisphere.
This eclipse of July 27, with the moon passing in the middle of the Earth's shadow, will be about as long as possible
Document originally published on Live Science
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