Coming Soon to New Jersey Skies: A Darkened Sun During a Solar Eclipse
A Rutgers professor of planetary sciences shares some eclipse dos and don'ts
On Monday, April 8, a total solar eclipse will cross North America, passing over Mexico, the United States and Canada.
From the vantage point of New Jersey, residents will witness a partial solar eclipse, weather permitting. Lujendra Ojha, an assistant professor with the Department of Earth and Planetary Sciences in the Rutgers–New Brunswick School of Arts and Sciences, studies how planets evolve, and how it affects their potential to develop the components necessary for sustaining life.
Ojha, known to all as “Luju,” joined the Rutgers faculty in 2019. He earned his doctoral degree in planetary science from the Georgia Institute of Technology and his bachelor’s degree in geophysics from the University of Arizona. While an undergraduate, Ojha discovered compelling evidence that briny water flows on Mars, a critical step toward identifying possible life on Mars.
He explained solar eclipses, their significance and what to expect on April 8.
What is a solar eclipse?
In very simple terms, the word “eclipse” refers to what happens when the light from a particular body is being blocked by another body. There are many kinds of eclipses in astronomy but, in this case, during the upcoming solar eclipse, the moon will pass between the sun and Earth and block the face of the sun.
We can very accurately predict when eclipses are going to happen. It’s all about physics. We know that the Earth is moving around the sun and the moon is moving around the Earth. It just so happens that, every couple of years, the stars align – no pun intended – and the moon gets right between Earth and sun. When this happens, the sunlight diminishes significantly. It looks like it's dark in the middle of the day.
Where and when can the April 8 solar eclipse be seen?
To view a total solar eclipse, you will have to be located within a long but narrow path, usually less than 150 miles wide, called the path of totality. This path will run through 15 U.S. states.
A partial solar eclipse, however, will be visible across a much larger area, but not large enough to include every part of Earth. The partial eclipse will be visible from most of North and Central America. An eclipse map, like the one I’ve constructed, shows where the eclipse will happen and what type of eclipse is visible in different locations.
Viewers in New Jersey, according to astronomical calculations, will start to see a partial total eclipse April 8 at 2:09 p.m. The eclipse will peak at 3:24 p.m. then diminish, finishing up at about 4:35 p.m.
Why does the viewing differ, depending on a person’s position on Earth?
Imagine that a candle is in front of you. If you stuck your thumb straight out, you would not be able to see the candle anymore. But your thumb might not completely block the view of the candle for a person sitting next to you, seated at a slightly different angle. The reason a viewer in New Jersey won’t see a total eclipse is that they are like the person watching the candle from the side. The path of totality doesn’t go over New Jersey because of the specific alignment of the Earth, moon and sun on that date.
Another contributing factor to the unique view is something known as “angular size.” The sun and the moon have the same angular size – despite their difference in mass, they look to be similarly sized from Earth. The sun is about 400 times wider than the moon, but it is also about 400 times farther away. This allows the moon to block the sun during eclipses.
How can you observe the eclipse? Are there any safety issues to be concerned about?
No one needs a telescope to see an eclipse. If the weather is clear, the sun will be visible in the sky. The eclipse can be viewed by those wearing specialized eye protection, such as eclipse glasses, a solar viewer or through a telescope with a solar filter. People can also use an indirect viewing method, such as a pinhole projector.
Even with protective glasses, viewers should not stare continuously at the sun but only look occasionally.
There is no danger, whatsoever, to being outside during an eclipse.
What should you expect to see?
For those witnessing a partial eclipse, the sun will consistently appear crescent-shaped, as though it is a cookie with a bite taken out of it. It will never darken completely, the way it would during a total eclipse. That “bite” will swell and then diminish as the eclipse progresses.
In the path of totality, at the very moment when the moon completely covers the sun, the sky will become dark, as if it were dawn or dusk. For those who experience a partial solar eclipse, the sky will appear slightly darker than it was before the eclipse, depending on how much the moon blocks the sun in their location.
Are eclipses unusual? When is the next one?
Total eclipses happen once every 18 months in some place on the Earth. The April 8 eclipse will be the last total solar eclipse visible from the contiguous United States until 2044. The last partial solar eclipse visible from New Jersey occurred in August 2017.
How are eclipses predicted?
Astronomers first must work out the geometry and mechanics of how Earth and the moon orbit the sun under the influences of the gravitational fields of these three bodies. From Newton's laws of motion, they mathematically work out the motions of these bodies. Scientists then feed the current positions and speeds of Earth and the moon into these complex equations and then program a computer to "integrate" these equations forward or backward in time to calculate the relative positions of the moon and sun as seen from the vantage point of Earth. Current eclipse forecasts are accurate to less than a minute in time over a span of hundreds of years.
Do scientists learn anything from the occurrence of a solar eclipse?
Yes, there's a lot of observations that happen. Eclipses help scientists make new discoveries about the sun, Earth and our space environment. Total solar eclipses allow scientists to see a part of the sun’s atmosphere – known as the corona – that’s too faint to see against the bright light of the solar disk. As a planetary scientist who also studies exoplanets, I find it interesting to note that eclipses in other star systems caused by planets blocking their suns helps us detect these planets that are beyond our solar system.
