Thursday, September 23, 2021

Rare type of annular solar eclipse to occur on April 29


An annular solar eclipse, where the sun looks like a ring of fire to observers on Earth, will occur on Tuesday, April 29, and be visible only in Antarctica, while a partial eclipse will be visible on the island nation of Tasmania, in Australia, and the South Indian Ocean.

No parts of the eclipse will be visible from the Americas, as it will occur during the night in this part of the world. The eclipse ranges from a point between South America and Antarctica through points in mid-Australia. The greatest eclipse will be visible for about six minutes in the corner of Antarctica, but the sun will be on the northwest (azimuth = 318.0°) horizon (altitude = 0.0°).

Circumstances of the eclipse

The northern edge of the antumbral shadow first touches down in Antarctica at 01:57:35 AM, EDT (UT-4 hours), NASA’s Goddard Space Flight Center reports. The instant of greatest eclipse, when the distance between the moon’s shadow axis and Earth’s geocentre reaches a minimum, occurs just six minutes later at 02:03:25 AM, EDT. For an observer at the geographic coordinates nearest the shadow axis (131° 15.6′ East longitude, 79° 38.7′ South latitude), the sun would appear on the horizon during the 49-second annular phase. Six minutes later (02:09:36 AM, EDT), the antumbral shadow lifts off the surface of Earth as the annular eclipse ends. The entire zone of annularity appears as a small D-shaped region in eastern Antarctica.

Why this eclipse is rare

Very few solar eclipses are annular to begin with. For example, in the series of this eclipse, known as Saros 148, which runs from Sept 21, 1653, through Dec 12, 2987, there are 75 solar eclipses, including 32 partial eclipses, 40 total eclipses, one hybrid eclipse, and only two annular solar eclipses. Some series have more, though.

But of the 3,956 annular eclipses occurring during the 5,000-year period from 2000 BCE to 3000 CE, only 68 of them, or 1.7 percent, are classified as non-central annular eclipses, like this one. That means the central axis of the moon’s antumbral shadow completely misses the Earth, while only one edge of the shadow touches the Earth.

In the illustration at right, provided by the UK Hydrographic Office, you can see what we mean about this eclipse being non-central. It comes close, but never quite gets to the center of the moon’s shadow anywhere on Earth.

On the site, you can also view animations of local views of the eclipse. For example, if you choose Perth, Australia, on the western edge, you’ll see the entire partial eclipse, but in Melbourne, in the east, you’ll see only part of the partial eclipse, because the sun will set before it’s over.

Two eclipses remain in the 2014 calendar year: a total lunar eclipse on Oct 8, and a partial solar eclipse 15 days later, when the moon gets to the other side. The northwestern third of North America will see all stages of the total lunar eclipse, while most of the partial solar eclipse will be visible from the US and Canada. In the lunar eclipse, the moon is just two days post-perigee, and it will appear about 5 percent bigger in the sky than it did during the total eclipse on April 15.

Paul Katula
Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.

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