Eclipse fever has gripped the world, but why is this eclipse such a big deal? Not only will today's total solar eclipse be a jaw-dropping celestial spectacle you’ll never forget – it presents a rare opportunity for scientists. It will allow them to study various phenomena, offering valuable insights into solar physics, Earth’s atmosphere, and the interaction between the two.
The difference between a 99 per cent partial eclipse and 100 per cent totality is quite literally the difference between night and day. But don’t worry if you can’t make it to the path of totality, it will be a day to remember for society and science regardless.
Related: Solar eclipse 2024: How to see the biggest cosmic event of the year this April
1. Solar activity is peaking
When totality hits, the most spectacular sight will come from the Sun’s corona – a fiery halo of plasma (hot, ionised gas) – around the silhouette of the Moon.
Back in 2017, when the last total solar eclipse cast its shadow on US soil (that particular eclipse stretched from Oregon to South Carolina), the Sun was near a 'solar minimum’.
The Sun goes through an 11-year cycle, known as the 'solar activity cycle'. It’s characterised by regular and observable fluctuations in the number of sunspots and solar activity. This activity reaches a maximum and minimum approximately every 11 years, driven by changes in the Sun's magnetic field.
“During the 2017 total solar eclipse that crossed the United States, the Sun had just entered a quiet phase. But for this year’s total solar eclipse, the Sun is in peak activity, which will give us a different view of the solar corona during totality,” Dr Darren Baskill, an astronomer from the University of Sussex, explains.
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This period of peak activity is called a ‘solar maximum’. And it's where the frequency and intensity of solar activity are at their highest. This means that there are more sunspots and solar flares this year. And, for us, this means a more exciting and visually spectacular corona that will be visible around the silhouette of the Moon at totality.
Wouldn’t it be great if a coronal mass ejection happened at the same time? Now there’s a front-page story.
2. The planets will align
For a brief moment, some of the other planets in the solar system will become visible, and they will appear in a slightly wonky line:
Jupiter > Mercury > Eclipse > Venus > Saturn > Mars
At -3.78 magnitude (the lower the magnitude, the brighter the object), Venus will become the brightest object in the sky, visible to the right of the eclipse.
You should also be able to pick out a well-positioned Jupiter to the left. Saturn and Mars will be sitting close together but further out, past Venus. They might be a bit trickier to spot, but they’re there.
Mercury will also be loitering close to the left-hand side of the Sun, but it’s too dim to see with the naked eye unfortunately.
3. You might also be able to see a comet
But it’s not only the planets that we’ll be able to see, as the Sun’s light is blocked out by the Moon. We may also be treated to a glimpse of the rare Devil Comet (aka 12P/Pons-Brooks), which may reveal itself to the naked eye.
If it’s bright enough, the Devil Comet (so-called because of its unusual ‘horned’ appearance) will be positioned near Jupiter, between Jupiter and the eclipse.
Taking into consideration the alignment of the planets, the peak in solar activity and the potential for a rare comet to be visible – all in the same region of sky – makes the 2024 total solar eclipse special in itself. But wait, there’s more.
Related: How to see the Everest-sized ‘Devil Comet’
4. The 2024 total solar eclipse might be the most convenient ever
Not only is the path of totality carving across Mexico, the US and Canada, but it has also decided to travel across where people actually live.
This eclipse is simply more readily accessible to a larger percentage of the population.
Contrast this to an eclipse that happens over the ocean, or a less populated continent like Antarctica, for example, and it wouldn’t be nearly as exciting.
Although thousands of people will be travelling to see the eclipse (including many from the UK), this accessibility will offer millions of Americans the opportunity of a lifetime, without extensive travel.
As a result of it scooting across major cities and urban centres (looking at you, Dallas), there’s more widespread public interest and engagement this time around.
5. There’s a long wait until the next one
Quite simply, this eclipse in this location is rare. Although the US doesn’t have as long to wait as the UK (which won’t see another total eclipse until 2090), this will be the last total solar eclipse in the contiguous US until 22 August 2044.
And even then, the 2044 eclipse will only be visible over Montana, South Dakota, and North Dakota. After that, it will head into Canada, where it’ll be visible from Alberta, the Northwest Territories and Nunavut, before ending in Greenland.
Even though somewhere on Earth will experience a total solar eclipse approximately every 18 months or so, due to the narrow path of totality, they are very rare for any one specific location. So, to have a total solar eclipse that covers so much of a populated landmass, regardless of the location, is quite spectacular.
Prior to the 2017 total solar eclipse, it had been over one hundred years since the last one swept across the contiguous US in 1918. Some locations can wait 400 years between solar eclipses!
- Related: When is the next solar eclipse?
6. At some point in the future, Earth will never witness another total solar eclipse
Did you know the Moon is drifting away from the Earth? It’s moving away from us at a rate of around 3.8cm per year – that’s roughly the same speed as our fingernails grow. At some point in Earth’s future, total solar eclipses will cease to exist, and nobody on our planet will ever witness one again.
Now, the Sun appears to us as being around 400 times wider than the Moon, and (conveniently) lies around 400 times further away. But as the Moon drifts away, it will become too small to completely cover the Sun.
“Total solar eclipses will no longer be visible from Earth, and all solar eclipses will become annular (or partial) eclipses,” says Baskill.
“Don’t panic, though, as this won’t happen for another 600 million years! And by then, space travel will allow us to fly a bit closer to the Moon to carry on enjoying total solar eclipses!” he adds.
Perhaps this is something to think about when you watch today’s eclipse; how incredibly fortunate we are, that humans exist at a time when conditions are just right to create this profoundly beautiful and otherworldly experience.
7. The 2024 total solar eclipse is the most dramatic type of solar eclipse
Of all the different types of eclipse (partial, annular or lunar), a total solar eclipse is by far the most dramatic. It’s simply an unforgettable experience. The perfect alignment of the Earth, Moon and Sun allows the Moon to completely cover the Sun, turning day to night for one brief, magical moment. But it’s not just the darkening of the sky that will leave you awestruck.
Bailey's Beads
In the moments before and after totality, Bailey's Beads will appear as fleeting, shimmering pearls of light around the Moon's edge. They’re caused by the last rays of the Sun streaming through the valleys on the Moon, quite literally highlighting the jagged and undulating lunar terrain.
The Diamond Ring
As totality nears, Bailey’s Beads will give way to the Diamond Ring. When just a single bright point of sunlight remains, peeping out from behind the silhouetted Moon, it will create the appearance of a ring with a dazzling ‘diamond’ set into it.
Shadow Bands
But we’re still not done. At the last gasp just before totality, we’re likely to see something called ‘shadow bands’. These are long, thin, wavy lines – ripples – of alternating dark and light that will spread rapidly across the ground. Shadow bands are most likely caused by Earth’s atmosphere bending the very last rays of sunlight, and it’s one of the more eerie phenomena that will accompany today’s eclipse.
The chromosphere
Then, for totality itself, we’ll be treated to a view that’s otherwise completely invisible to us, the Sun’s atmosphere. This is made up of the chromosphere and corona. The chromosphere will appear as a narrow, reddish-pink ring, perhaps with bright, gaseous features called ‘prominences’. These will appear as glowing tendrils, shaped like loops or arcs.
These prominences often extend into the Sun’s outer atmosphere, called the corona – this is what we really want to see.
The corona
Appearing as a delicate, ethereal halo of pearly white light surrounding the dark silhouette of the Moon, the sight of the Sun’s corona promises to be spectacular. Streamers, plumes and loops will dance outwards, providing a stark contrast against the darkened sky.
8. NASA are launching rockets to study the effect on the ionosphere
Solar eclipses cause changes in the ionosphere, an electrified region of the upper atmosphere filled with charged particles, and this can affect the electric field around Earth. It will trigger large-scale atmospheric waves, as well as small-scale disturbances (‘perturbations’).
During an eclipse, the sudden reduction in sunlight causes the ionosphere to cool, which can alter its conductivity and density. These changes can lead to fluctuations in the Earth's electric field, which in turn affect radio waves, GPS and communication systems.
To study these short-term changes at exactly the right time and place, NASA is launching sounding rockets as part of their Atmospheric Perturbations around Eclipse Path (Apep) mission.
Sounding rockets are a type of (relatively inexpensive) research rocket, which are designed to carry scientific instruments into suborbital space. These particular rockets are expected to reach a maximum altitude of 420km (260 miles) and will measure the charged and neutral particle density, and surrounding electric and magnetic fields.
Three rockets will be launched in succession: 45 minutes before totality, during, and 45 minutes after the peak local eclipse at NASA’s Wallops Flight Facility in Virginia.
9. You can take part in making a 2024 total solar eclipse megamovie
Although this sounds like it could be the codename for the latest top-secret Hollywood blockbuster, the Eclipse Megamovie 2024 is actually a citizen science project. If you’re planning on (safely) taking pictures of the event, you can help produce a high-def, time-expanded video of the whole eclipse. Not to mention you’ll be contributing to real scientific research.
This exciting, NASA-funded project aims to uncover more about the secret lives of solar jets and plumes, and their interactions with solar wind – the stream of charged particles released from the upper atmosphere of the Sun.
Your photographs will help identify solar jets as they leave the Sun's surface and solar plumes as they grow and develop.
10. NASA is chasing the 2024 total solar eclipse with high-altitude planes
Flying above the (hopefully non-existent where you are) clouds, 50,000 feet in the air will be NASA’s high-altitude research planes, the WB-57s. Flying at around 460 mph, the jets will quite literally chase the Moon’s shadow during the 2024 total solar eclipse.
As a result, they will experience totality lasting around 25 per cent longer than on the ground; 6 minutes and 22 seconds. And this means more data.
Carrying suites of scientific instruments, the planes will measure the temperature and chemical composition of the corona and coronal mass ejections, take high-res images of the solar atmosphere, and measure how charged Earth’s ionosphere is. The experiments may even reveal asteroids that are orbiting close to the Sun.
Why is the Sun’s corona millions of degrees in temperature, when the surface of the Sun is just 5,000C (9,000F)? This mission hopes to provide some clues.
Imagine explaining all that to the viewers of the 1918 eclipse – back then, it was a mere 15 years after the Wright Brothers flew the first-ever powered aeroplane.
11. 600 balloons will be released into the atmosphere
As part of the Nationwide Eclipse Ballooning Project, 53 teams across the US are sending around 600 balloons into the atmosphere. Equipped with instruments, the balloons will study gravity waves, humidity, wind direction and wind speed, as well as livestreaming the event.
Aimed at STEM students, the project will observe in situ perturbations in atmospheric phenomena. It will enable learning opportunities, including career skills and cultural perspectives, but will address real science, with the results presented in peer-reviewed papers.
Key research areas include measuring the extent of eclipse-induced gravity waves, temperature variations in different parts of the atmosphere, whether variations in temperature and wind are instantaneous or time-lagged, as well as providing a real-time benchmark for current high-res weather-forecasting models.
In short – there’s a lot of science going on during this eclipse.
About our expert
Dr Darren Baskill is an outreach officer and lecturer in the Department of Physics and Astronomy at the University of Sussex. He previously lectured at the Royal Observatory Greenwich, where he also initiated the annual Astronomy Photographer of the Year competition.
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