Catherine Pilachowski, Distinguished Professor of Astronomy and the Daniel Kirkwood Chair in the IU Bloomington College of Arts and Sciences, explains what will happen during the 2024 eclipse.
Question: What is a total solar eclipse?
Answer: A total solar eclipse happens when the moon passes in front of the sun and completely blocks our view of the sun. At any given spot on Earth, on average, we can see a total eclipse about once every 375 years. So, not very often. The last one here in Bloomington was in 1869, so we’re pretty lucky to have one this soon
Q: What determines if a city will be in the path of totality?
A: We see a total eclipse every year or two on the Earth, but always in a different location. And that depends exactly on where the moon is in relation to the sun and the Earth.
The moon is about one-quarter the size of the Earth, and it lies about 400,000 kilometers away from the Earth, orbiting around the Earth. When the moon falls directly between the Earth and the sun, it casts a shadow on the Earth.
It’s just big enough that it can completely block the sun during the total eclipse. What that means is that the point of the full coverage of the sun is a fairly small dot on the side of the Earth. And that dot moves across the face of the Earth as the moon moves around its orbit and the Earth rotates on its own axis. The location of the spot of darkness depends exactly on where the moon is in relation to the Earth.
Q: What will people who are in the path of totality experience during the eclipse?
A: First, it will get dark during the four minutes of totality. Viewing the eclipse safely means having a solar viewer of some kind during the partial phases — specifically, eclipse glasses that are safe for looking at the sun.
Never ever look at the sun — even a partially covered sun — with the naked eye. But, during totality, toss that viewer aside and just look. We’ll be able to see the glow around the sun from the solar corona — this is material that is being blown away from the solar surface. And, if we’re lucky, we’ll see prominences around the edge of the moon.
I find that as a total eclipse occurs, I am just mesmerized by the phase of totality. Being able to see the planets in the sky — all five of the classic naked-eye planets will be in the sky around the sun during the total eclipse phase in 2024. Mercury, Jupiter, Saturn, Venus and Mars will all be up there, although Mercury will be too faint to see.
Q: How could the weather impact the 2024 eclipse?
A: If the weather is cloudy, we will experience total darkness, but we won’t be able to see the sun or the planets or the stars in the sky. We’ll be able to see interesting effects as the total eclipse phase approaches.
We’ll see darkness approaching on the southwestern horizon. It will get totally dark here in Bloomington, and then we’ll see it brighten on the southwest horizon and we’ll see the northeast side darken. So, we’ll be able to watch for those phenomena in the sky. But we won’t be able to see the total phase ourselves.
Historically on April 8, we have about a 40 percent chance of clear weather and a 60 percent chance of cloudy weather.
Q: How is the 2024 eclipse different from the 2017 eclipse some Indiana cities experienced?
A: The eclipse in 2017 was only about 94 percent of the sun’s disc covered, so that means we still had a view of at least a portion of the sun; it was still daylight in Bloomington. With a total solar eclipse, the sun is completely covered, and we will have four minutes of darkness — no sunlight at all.