A Clue Hidden in Sunlight
How can scientists find out what the Sun is made of without taking a sample? One answer is hidden in its light. In 1868, a thin yellow line in sunlight gave scientists a clue to an element they had not yet identified on Earth.
On August 18, 1868, French astronomer Pierre Janssen observed a total solar eclipse from India. During a total eclipse, the Moon briefly blocks the Sun’s bright surface. This makes it easier to study features around the Sun that are usually lost in the glare. Janssen used an instrument called a spectroscope to examine light from the Sun’s outer atmosphere.
A spectroscope separates light into a band of colors called a spectrum. Within that spectrum, scientists can see narrow lines. Different chemical elements produce patterns of lines at particular positions. These patterns act like clues: by comparing them with lines produced by known elements on Earth, scientists can identify materials in distant objects.
Janssen noticed a bright yellow line in the Sun’s spectrum. At first, it was thought to be connected to sodium, an element already known on Earth. But the line did not quite match sodium’s familiar yellow lines. That small difference mattered. It suggested that another substance might be producing the light.
- element:
- A basic substance made of one kind of atom.
- glare:
- A bright light that makes it hard to see.
- atmosphere:
- The gases surrounding a star or planet.
- independently:
- On one’s own, without relying on another person’s work.
- proposed:
- Suggested an idea for others to consider.
- dispute:
- A disagreement or argument.
- mineral:
- A naturally occurring material found in Earth.
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Preview questions from this passageShowHide
- 1How can scientists identify elements in a distant object without taking a sample?
- 2Why was a total solar eclipse helpful to Janssen’s study of the Sun?
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About this explanatory article passage for Upper Elementary
“A Clue Hidden in Sunlight” is a explanatory article reading passage about The discovery of helium, written for Upper Elementary. It takes about 3 minutes to read (461 words) and comes with an interactive quiz and a printable worksheet with comprehension questions and an answer key.