Where can I see Baily’s Beads on 8 April 2024?

Baily’s Beads as seen during the 2017 total eclipse (NASA/Aubrey Gemignani)

One solar eclipse phenomenon prized by photographers is Baily’s Beads - the “ string of pearls ” that can appear in certain circumstances around the times of second or third contact.

The appearance of the beads requires the Sun and Moon to do a very particular dance whereby the Moon obscures the Sun at a point on its edge (or ‘limb’) where the surface is particularly uneven. Although it appears essentially smooth to the naked eye, the Lunar surface is in fact very uneven, with various large valleys and mountains.

During an annular eclipse, the mountains of the Moon break through the edge of the Sun’s bright photosphere as it moves in and out of the solar limb.

During a total eclipse, the light of the Sun lingers on, shining through the lunar valleys - but only if the circumstances are right!

How can we know? Is it a matter of luck?

The Lunar Limb

Astronomers have for many years sought to improve their maps of the moon. Observations from Earth using telescopes, and later, cameras, provided the earliest maps. In recent years, space-based mapping has been the go to method. The Japanse SELENE mission, popularly known as Kaguya provided a detailed map of the lunar surface in 2009. More recently, NASA’s Lunar Reconnaissance Orbiter has also mapped the Moon.

Happily for eclipse chasers, both missions have yielded data that allows us to predict and simulate exactly where and when Baily’s beads will appear for any solar eclipse.

Traversing the path through Texas

The upcoming April 8 2024 total eclipse passes over Mexico, Texas, and sweeps on northeastwards towards Canada’s Atlantic provinces. If you want to see Baily’s Beads, where should you go? We can use the eclipse simulator in Photo Ephemeris to find out.

Let’s look at some potential locations in Texas. We’ll start near the northern limit of the eclipse and work our way south, traversing the central line:

Our locations are:

• Near Comanche
• Hamilton
• Gatesville
• Temple
• Near Cameron

What should we be looking for? To get an idea of that, let’s start by taking a look at the lunar limb profile:

Lunar limb at max eclipse in Gatesville, TX

The orange line shows an exaggerated relief profile of the lunar limb. The blue circle is the default ‘smooth limb’: you can compare the two to identify lunar peaks and valleys. Two things to note:

• The roughness varies: you can see some areas are significantly more varied than others
• The profile you see depends on the time and place: the Moon’s libration and observer’s location change the profile you see

That said, here’s an insider tip for searching for Baily’s beads locations: the limb profile only varies a little during the eclipse from the northern limit of the path to the southern in a given geographic area.

Three more tips. Generally speaking:

• the more varied the limb profile, the more interesting the beads will appear
• the deeper the valley, the longer a bead at that point on the limb will last
• the closer to the path limits you are, the longer beads may last (but totality will be shorter)

Looking at the limb profile above, the ‘interesting’ areas are at 2 o’clock, 4 o’clock, and from 6 to 9 o’clock. Locations where the eclipse contacts occur in those areas should give the most appealing Baily’s beads. Let’s see what we find.

The image below shows how Baily’s beads will appear right at second contact (left) and at third contact (right) at each of our five locations:

Baily’s Beads at standard contact times, 8 April 2024

These are the standard ‘spherical Moon’ contact times - i.e. not adusted for the effects of the lunar limb. These are the times you’ll typically see quoted online. Look closely at each image - in particular the area underneath the yellow line. The yellow line shows the areas where beads are possible. Underneath you’ll see some bright white areas - those are the actual beads visible at this time and at each location.

What does it tell us? A few observations:

• There’s nothing going on at C2 (start of totality), except near Comanche, TX near the northern limit
• C3 (end of totality) is generally more interesting: every location except Temple, TX shows some beads at C3
• You can be on the centerline at Gatesville and see Baily’s beads - however, they’re not going to last terribly long
• At Hamilton, the beads are already prominent and joined together at C3: this means that totality is shorter than advertised using the standard times. Why? Because the contact occurs at a point where the lunar limb is depressed below the average radius (the blue line)

Next, the image below shows how Baily’s beads will appear at 5 seconds before second contact (left) and 5 seconds after third contact (right) at each of our five locations:

Baily’s beads at 5s before C2 and 5s after C3, Apr 8 2024

It looks like we have the potential for beads in all locations. However - what still images from the simulator cannot capture is how the beads evolve over time and how long they last. It’s important to play back the contact times in the simulator to get a real sense of what can be observed.

Also, beware: just because the locations near the central path appear to show more ‘bright’ areas, that doesn’t mean you’ll perceive them as beads: the Sun’s photosphere is so bright, that too much of it, and you cannot discern the individual beads any more. They need to be small and separated in order to be seen clearly (or you need a solar filter on your lens).

Nonetheless, an interesting pattern emerges. If we play ‘join-the-dots’ with the apparent positions of the beads between C2 and C3 for each location, you can see how your position in the path determines where the contacts will occur:

Contact angles (approximate) by location

If you’ve visually identifed where the ‘interesting’ beads might appear from the limb profile on the central line, you can work out whether you need to head north or south in order to ‘place’ the contacts over your target limb area.

The conventional wisdom amongst Baily’s beads hunters is to head towards the southern limit for total eclipses. The rationale is clear from the diagrams above: near the southern limit, the contacts occur in the 6 to 9 o’clock region of the limb. Indeed, around C3 in particular, the beads appear to last around 20 seconds, with some attractive patterns emerging.

Click to watch the simulation play out at 5× speed. We start around 20 seconds before C2 and continue until ~30s after C3. You’ll notice that the beads around C3 last nearly 40 seconds:

But look also at Gatesville, right on the central path. Beads also form around C3:

The downside is: they don’t last long at all (maybe 3-4 seconds) before the Sun’s photosphere overwhelms and a traditional diamond ring forms. However, if you’re ready for them, you can photograph them - timing and continuous shooting are key.

Summing it up

• For the longest-lasting and most visually interesting beads, head towards the southern limit (for a total eclipse) - but it’s at the expense of time in totality
• You can see beads on the central line, but they’ll be fleeting: be prepared, know your timings, and take LOTS of exposures!
• Some locations will give you a taste of everything, particularly if you identify the ideal contact points for Baily’s beads (areas of greater roughness)
• Do your research: use the simulator in Photo Ephemeris Web and Photo Ephemeris for iOS to plan your April 8 eclipse shots