For some this will be the last time! You don’t see ‘em often, but when you do – time to take advantage. Next week Montana will be privileged to view the last viewable Eclipse from Montana for many a year. On April 8, 2024, a total solar eclipse will be visible from Texas to Maine. The next opportunities to experience a total solar eclipse over the United States will be in 2044 (in North Dakota and Montana) and 2045 (as it crosses from California to Florida).
What causes a solar eclipse? The first thing to understand about solar eclipses is that they occur because of a remarkable cosmic coincidence: the Sun is about the same apparent size in our sky as the Moon. While the Sun is actually about 400 times larger in diameter than the Moon, the Moon is also about 400 times closer than the Sun. Therefore, the Sun and the Moon appear to be about the same size in our sky.
This single fact explains why we see total solar eclipses – the Moon has an apparent size that just barely covers the Sun completely, yet is not too large that the Sun’s atmosphere, its corona, is eclipsed as well. We on Earth occupy a celestial sweet spot to witness this sight. We are the beneficiaries of a wonderful cosmic coincidence, lined up like a cosmic billiard shot.
It was not always so. When the Moon first formed around our Earth over 4 billion years ago, it was much closer to the Earth and appeared much larger in our sky. So total solar eclipses in the early epochs of our Earth did block the Sun but also most of the corona. Over the eons, the Moon has been gradually receding from the Earth due to the friction from the tides. At present, the distance from the Earth to the Moon increases by about an inch per year. In some distant future epoch, the Moon’s disk will become smaller such that no more total solar eclipses will be visible from Earth.
Not every eclipse of the Sun is a total eclipse. Sometimes, the Moon is too small to cover the entire Sun’s disk. The Moon’s orbit around Earth not perfectly round but is oval or elliptical in shape. As the Moon orbits our planet, its distance varies from about 221,000 to 252,000 miles. This 13% variation in the Moon’s distance makes the Moon’s apparent size in our sky vary by the same amount. When the Moon is on the near side of its orbit, the Moon appears larger than the Sun. If an eclipse occurs at that time, it will be a total eclipse. However, if an eclipse occurs while the Moon is on the far side of its orbit, the Moon appears smaller than the Sun and can’t completely cover it.
There are 5 distinct stages of an annular solar eclipse: 1st contact—partial eclipse begins: The Moon’s silhouette starts becoming visible in front of the Sun’s disk. The Sun looks as if a bite has been taken from it.
2nd contact—full eclipse, or annularity, starts: The ring of fire appears. For a few seconds just as the annularity begins, Baily’s beads, which look like beads of light, can sometimes be seen at the edge of the Moon’s silhouette.
Maximum eclipse: The Moon covers the center of the Sun’s disk.
3rd contact—annularity ends: The Moon starts moving away from the disk of the Sun. Once again, Baily’s beads may be visible along the Moon’s leading edge.
4th contact—partial eclipse ends: The Moon stops overlapping the Sun’s disk. The eclipse ends at this stage.
Annular eclipses can last over 3 hours in locations where annularity is visible. From start to finish, the total duration of annular eclipses can be over 6 hours but not in a single location. The annularity, when only a ring of fire is visible in the sky, can range from less than a second to over 12 minutes.
Cascade’s eclipse will be visible on October 14 beginning around 9:12:21 a.m. The Partial solar eclipse will be visible at 68.21% coverage of the Sun. The Duration will be 2 hours, 37 minutes, and 48 seconds or ending at 11:50:09 am.
The Library will be hosting a program with solar eclipse glasses free to the public and access to a solar eclipse telescope. Our program will begin at 8:00 a.m. and run throughout the eclipse activity Saturday October 14 in front of the Library. We will have water and refreshments available. Feel free to stop by for a minute or for the whole shebang.