Annular eclipse — solstice ring over Taiwan (2020)

On the solstice, a razor-thin ring (99.4 % covered) from Africa over Tibet to Taiwan — a one-minute thread of light at Chiayi.

The moment of Annular eclipse — solstice ring over Taiwan (2020): https://nowsky.org/e/annular-eclipse-2020 — opens at the right place and time, replayable, no login.

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The story

21 June 2020 was the northern solstice, and on that day a thread-thin ring of fire crossed the Earth. The Moon covered 99.4% of the solar disk, leaving only a filament of light around the rim, and nowhere did the ring stay closed for more than 38 seconds — as close to the boundary between total and annular as eclipses come.

The path began in the DR Congo, crossed South Sudan, Ethiopia, Yemen and Oman into the Arabian Sea, then Pakistan and northern India (Kurukshetra, Dehradun), the Tibetan plateau and southern China (Xiamen), reaching southern Taiwan before ending in the Pacific south of Guam. The Himalayan and Tibetan stretch ran over nearly empty high ground.

At Chiayi in Taiwan the ring lasted barely a minute around 16:13. Taiwan's main island rarely falls inside an annular path, so observers converged from across the island, told that the next chance would not come until 2215. Even at 99% coverage the surviving rim was bright enough that the sky only dimmed to an overcast-afternoon level.

The first half of 2020 was the pandemic's travel freeze. Public events in India and Taiwan were capped or replaced by live streams, and many people watched from a rooftop with a single filter. The sky replay shows that Chiayi afternoon; the orbit view shows the shadow slicing diagonally across Asia.

Why it matters

Coverage of 99.4% teaches how different "almost total" is from total. In a total eclipse the last 0.1% vanishing brings corona, prominences and stars all at once; an annular never crosses that threshold and sunlight keeps command of the sky. This eclipse was a textbook demonstration of how steep that threshold is.

A thin ring is extremely sensitive to the lunar limb. Instead of closing cleanly it broke into chains of Baily's beads along mountain ranges for extended stretches, and campaigns in India, China and Taiwan used the beads to measure the solar radius and lunar terrain simultaneously.

The solstice coincidence was chance but resonant: on the longest day of the northern year the Sun briefly shrank to a ring, an image recorded alongside midsummer festivals in many places.

How to watch

Annular track: the Congo, South Sudan and Ethiopia (morning) → Yemen and Oman → Pakistan and northern India (late morning) → Tibet and southern China (Xiamen, afternoon) → Chiayi, Taiwan (16:13) → the sea south of Guam. Partial phases covered East Africa, the Middle East, South Asia, China and South-East Asia; Seoul saw about 45% covered around 4 p.m.

The thinner the ring, the more the filter matters — even 0.6% of the Sun is dangerous to the naked eye. With annularity lasting around a minute, fixing camera exposure in advance and shooting the bead chains continuously on either side gives the best results.

The sky replay tracks the Sun over Chiayi and slows for the ring; switch the location to Seoul for that afternoon's partial.

See this for yourself — open that sky at that moment · replay the moment in the orbit view

Background

The eclipse is the 36th of Saros 137. Its predecessor on 10 June 2002 was an annular over the Pacific; its successor on 2 July 2038 crosses the Atlantic and Africa. Series 137 is in transition from annular to total, so its rings grow thinner with each return.

Six months earlier, on 26 December 2019, an annular had crossed the same southern India and South-East Asia; six months later, on 14 December 2020, a total eclipse crossed Chile and Argentina. Even in a pandemic year there were two central eclipses.

Taiwan's previous annular was on 19 April 1958 and the next is in 2215. Kurukshetra in northern India, a site of Hindu eclipse pilgrimages, was a place where observation and religious observance overlapped.

The annular eclipse of 21 June 2020 fell on the solstice itself, a rare coincidence, with a path from Congo through Ethiopia, Yemen, Oman, Pakistan, northern India, Tibet and China to Taiwan and the Pacific. With 99.4 percent of the Sun covered it was among the thinnest rings of any annular eclipse, and at Chiayi in Taiwan the ring held for less than a minute. It was an eclipse on the borderline — a slightly closer Moon would have made it total — and for moments the Sun’s rim broke into beads like Baily’s beads.

FAQ

Why did the sky not go dark?

Even with 99.4% covered, the remaining 0.6% shines at full photospheric brightness. The darkness of totality arrives only when the last 0.1% goes.

How long was the ring at most?

38 seconds at maximum; Chiayi had a little over a minute on the centre line.

How much was covered from Korea?

About 45% around 4 p.m. in Seoul; no ring.

When is Taiwan's next annular eclipse?

Calculated for 2215; the previous one was in 1958.

Related

• The 2019 annular over Singapore
• The 2020 total eclipse over Chile and Argentina
• The 2021 Arctic annular
• The Moon — object index
• The Sun — object index

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Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.