Rapa Nui Annular Eclipse of October 2nd, 2024

Eclipse with the Mo'ai

Rapa Nui, also called Isla Pascua and Easter Island, is the southeastern-most inhabited island of Polynesia, about 3,500 kilometers west of South America. It's a five-and-a-half hour flight from Santiago, Chile. The island is controlled by Chile, but it definitely isn't a part of Chile.

I had gone to Chile in 2019 for a total solar eclipse. It would be foolish to travel that far just for a five-to-eight-minute event that might easily be invisible due to weather. We went to where the totality centerline crossed the edge of the Atacama Desert, north of La Serena, so the conditions were likely to be good, but even the Atacama provides no guarantee. I used the eclipse as an excuse for my first visit to Chile — Santiago, Valparaiso, and La Serena, then south through Middle Chile to Rancagua, Talca, and Constitución.

My friends had continued onward to Rapa Nui in 2019. When 2024 and the annular eclipse came closer, I decided that I needed to visit Rapa Nui. If it was cloudy on eclipse day, there was plenty to see and do on Rapa Nui anyway.

Orbits and Eclipses

What is an annular eclipse? It's when the Moon is slightly too far away from the Earth to completely cover the Sun's disc. The angular diameter of the Sun is greater than that of the Moon. There's a "ring of fire" effect, a thin ring of the Sun remains visible. This is a little confusing because Rapa Nui is within what is also called the Ring of Fire around the Pacific Ocean, tectonic plate boundaries where volcanos form and strong earthquakes occur. So I would be in one Ring of Fire looking at a distant Ring of Fire.

There are no integers involved in orbital mechanics. Everything moves along non-circular ellipses defined by irrational numbers. Orbits are not co-planar, and rotational axes are not parallel. Everything perturbs everything else.

The Moon's orbit around the Earth has an eccentricity of 0.0549. Its perigee or closest distance is nominally 362,600 km and its apogee or greatest distance is nominally 405,400 km. Given perturbations, those are actually 356,400–370,400 km and 404,000–406,700 km.

Then, the Earth's distance from the Sun varies, closest in early January and furthest in early July. The Earth's orbit around the Sun has a lower eccentricity, just 0.0167, so it is closer to being a circle than the Moon's orbit around the Earth. The aphelion and perihelion, Earth's furthest and closest distance from the Sun, are 152.10 and 147.10 million kilometers, respectively. (And, of course, slight perturbations also intrude here.)

All that means that the width of the Sun's disc as seen from the surface of the Earth ranges from 31.6' to 32.7' of arc, while the Moon's ranges from 29.4' to 33.5'. If the Moon's disc appears wider than the Sun's, a total eclipse is possible. But if it appears smaller, the Moon can't block the entire Sun and only an annular eclipse is possible. If the Moon is at or near apogee, only 29.4' wide, it simply isn't wide enough to block the entire Sun.

Using an online lunar perigee and apogee calculator, you can find that on 2 October 2024, the day of the eclipse, the Moon would go through apogee. It would be 406,516 km from Earth, very close to its maximum distance. The Earth would be half-way between its minimum and maximum distance from the Sun, so the Sun would appear about 32.15' wide. This could not be a total eclipse, the Moon would be too far away and it would not appear large enough.

A year before I had observed an annular eclipse in Roswell, New Mexico, and knew that it was still quite a sight. So, I planned to go to Rapa Nui and see many wonderful and interesting things, possibly including, if the weather was right, an annular eclipse.

The excellent Totality smartphone app from the American Astronomical Society helps you plan things. For annular eclipses of the future and past, follow its "More Future Eclipses" link to xjubier.free.fr.

The below screenshot shows how far Rapa Nui lies to the west of South America. The blue line is the centerline of the eclipse, the black circle is the point where the annular phase of the eclipse lasts the longest, and the red pin is slightly north of Rapa Nui.

Here's the view considerably zoomed in. The white dot is the island of Rapa Nui. Haŋa Roa is the town on the island.

Unlike in Roswell the year before, I couldn't simply drive to a spot directly on the centerline. Rapa Nui was about half-way from the centerline to the edge, where the annular ring is no longer complete. But, there would still be about six and a half minutes of the annular phase.

Four contact events are significant during an eclipse:

• 1st contact or C1 when the Moon first begins to move in front of the Sun.
• 2nd contact or C2 when the Moon has first moved entirely in front of the Sun.
• 3rd contact or C3 when the Moon reaches the other side and begins to move out from in front of the Sun's disc.
• 4th contact or C4 when the Moon no longer covers any of the Sun's disc.

From C1 to C2 is the first partial phase, C2 to C3 is the annular phase, and C3 to C4 is the final partial phase.

The events in local time, GMT-5, were:

Start of partial, C1	12:23:44.0
Start of annular, C2	14:03:55.9
End of annular, C3	14:10:20.9
End of partial, C4	15:52:17.1

A total solar eclipse had crossed Rapa Nui on 11 July 2010, the first such occurance in over 1,300 years. And now, a little over just 14 years later, here came an annular eclipse.

Palm Trees and Mo'ai

Yes, I was in Polynesia, there are some palm trees! There were some clouds, but the sky was mostly clear. Any clouds moved past the Sun within a minute or two.

You read about Easter Island "heads", but that's because many pictures show partially buried examples. The mo'ai are human figures with an elongated head and a torso and arms. The head is about three-eighths of a typical mo'ai statue.

The mo'ai depict deified ancestors, and were usually placed on platforms near the shoreline, looking inland to watch over the settlements. They depict specific ancestors, so each one is unique.

Some have pukao, red scoria topknots. Some have white coral eyes with black obsidian or red scoria pupils.

Notice the small blue crescent-shaped lens flares in the two pictures above, easily seen against the dark torsos of the mo'ai. That shows the shape of the partially eclipsed Sun. The lens flares are opposite the Sun around the optical axis, and so they are rotated 180°. I took these two pictures during the final partial phase as the Moon was moving off the Sun to the upper right as viewed from here.

Below is a picture of a cloud moving away from the Sun during the initial partial phase, getting close to the annular phase. Notice that there are two crescent-shaped lens flares. J.J. Abrams would approve, his movies are notorious for being filled with them.

Above is the result of cropping the original 3000×4000 image down to 750×1000 before resizing it to 600×800.

Observing the Eclipse

Of course you must use proper eye protection. It used to be that you were limited to shade 12 or darker electric arc welding glass. That meant you had to carry a piece of glass 60×110 mm in size.

Now, low-cost but safe eclipse glasses are available. But make certain that what you have meets the ISO 12312-2:2015 standard. They will have two "lenses" in a folding cardboard frame that easily fits into your shirt pocket. I saw my first total eclipse in Chile, Rapa Nui is administered by Chile, and Chile is a center of astronomical research given the conditions at high altitudes in the Atacama Desert north of La Serena. Quality eclipse glasses are easily found in Chile.

And, while eclipse glasses are too small for many camera lenses, you could hold them as a filter in front of your smartphone camera lens. That is, you could do that. But experiment a few days in advance, I expect that you will be as disappointed as I have been with the performance of a smartphone camera for eclipse photography, as shown below.

Human visual acuity for the ideal 20/20 vision is about 1' or 60" of arc, 1/60 of a degree. So, with your vision well-corrected with glasses you should be able to see features about 1/30 the width of the Moon. Put on your glasses, then put your eclipse glasses over those. Or maybe reverse the order, depending on the design of your glasses.

If you are observing a total eclipse, then you will want to use a camera during totality to capture the very eerie appearance of an absolutely black hole in the sky surrounded by the corona.

My Unimpressive Photography Results

Wear your eclipse glasses and enjoy your view of the first partial, annular, and last partial phases. But you may also be tempted to attempt to capture some pictures by holding a pair of eclipse glasses over your smartphone camera's lens.

The problem is that a typical smartphone camera simply can't handle the dynamic range of an almost entirely black frame with a tiny bright filtered Sun near the center.

The auto-exposure function can't decide what setting is appropriate, fluctuating constantly and only settling down on over-exposure. While that is going on, the auto-focus function can't keep up. When auto-focus does briefly settle on what seems to be a somewhat reasonable image, auto-exposure will almost immediately change its setting, the image of the Sun will swell into a fuzzy area, and the two are off on another random chase.

Your smartphone camera's "Manual" or "Pro" setting may allow you to make this behavior a little less bad. However, if you compare what you see on the phone's display to what you observe looking through your eclipse glasses, you will see that your filtered natural eyeball view is far superior.

Wear your glasses and enjoy the phenomena. Then you can look online or buy an issue of Sky and Telescope to see what the pros captured with filters on long lenses, manually focused with proper exposure times.

A lot of trial and error yielded a few fairly clean crescent images, although they're still not focused very well. The crescent appears here much thicker than it did when simply looking through the eclipse glasses, and the ends of the crescent appear rounded in these images.

The below two images are 300×300 samples of 3000×4000 JPEG images. These are in the initial partial phase, before annularity, with the Moon moving from about 8 o'clock to 1 o'clock across the Sun's disc as seen from Rapa Nui. The crescent was actually much thinner at this point, and its ends tapered to infintesimal points.

I tried using the 3× optical zoom and the 10× optical-plus-digital zoom. That required figuring out which of the three lenses on my Samsung S23 FE is used for 0.6×, 1×, and 3× optical zoom and shifting the filter appropriately. That's easy — adjust the zoom setting, point the camera at the ground, and watch the display as you move your finger in front of the lenses.

However, optical zoom results seemed promising at first but were generally much worse. Until the exposed crescent became very thin, all it produced was an orange blob.

For a short time on either side of the annular phase, 3× or 10× zoom could produce a crescent image on maybe one frame out of ten, but it was much worse focused than the tiny images with 1× zoom. See my trip to Roswell for results during the annular phase.

Some Promise for the Next Eclipse, Maybe

Crowds were in the parks along the waterfront, but they dispersed quickly after the annular phase of the eclipse.

During the final partial phase, I did pick up a tip from a couple who were able to get so-so results with a handheld camera. However, it almost requires two people using both hands.

Their trick was for one of them to hold the smartphone while the other held the filter, one lens of eclipse glasses, 2–3 cm away from the camera lens. You have to hold the two so the camera lens is looking through the center of the filter, so the Sun is near the center of the field of view. At the same time, tip and tilt the filter so the camera isn't seeing too much of a reflection of itself.

I think that the trick works (somewhat) because the auto-exposure function isn't presented with an image that is almost entirely dark. The edge of the filter and some reflection of the camera front are around the edges of the image, so the auto-exposure algorithm can stabilize on a setting. Then, the auto-focus algorithm is confronted with most of the image being the filter itself, far too close for it to focus. So, the image of the Sun is all that it has a chance of using. Here is a result I got:

Here is the result of cropping down the above picture, taken with the 1× optical zoom, and then doing similar with an image taken with 3× optical zoom.

However, remember that human visual acuity for corrected 20/20 vision is about 1' of arc, and the Sun's disk was about 32.15' of arc. The above two pictures do not resolve anything at close to 1/32 of the width of the crescent. Your view through eclipse glasses would still be much sharper than the above.

However, I may experiment with making a filter holder for my phone and trying it when there are "naked-eye sunspots", meaning that through eclipse glasses you can (barely) make out one or more sunspots.

Were animals confused by the annular eclipse the way they are by a total eclipse? Not that I could tell. The many stray dogs were intrigued by all the humans looking at the sky, but that was about it.

As in Chile, on Rapa Nui stray dogs are tolerated and even loved. However, when there are numerous stray dogs they have been through harsh selection for behavior. Only the most mellow are allowed to survive to breed, so within a few generations the dogs are very non-aggressive.

Making Notes

I went to the nearby Iti Lafken bar-restaurant across the street from the park. I organized some notes while having a local Mahina Brewery beverage. The brewery was just a little further out the road from where I was staying. Mahina means "Moon" in the Rapa Nui language, and I had just watched the Moon (mostly) cover the Sun. Notice the crescent and mo'ai in the logo on the label. Also, motu means "island".

Mike Rapu and two partners from the continent founded Mahina Brewery in 2008. They were also making a pale ale and a porter at the time of my visit. Producing beverages has been a family tradition for him. His grandfather made a corn distillate. But unfortunately, at the time all alcoholic beverages were illegal and he was sentenced to several lashes across the back, scarring him for life.

Next❯ Vaihū — Ritual Circle, Houses, and Gardens