Final answer:
The dark lines in the Sun's spectrum are caused by the absorption of specific wavelengths of light by atoms in the Sun's atmosphere, leading to the absence of light at those wavelengths when observed.
Step-by-step explanation:
The dark lines in the Sun's spectrum represent light that is absorbed by the Sun's atmosphere. These lines, known as Fraunhofer lines, occur because atoms in the Sun's cooler outer atmosphere absorb certain wavelengths of light, creating dark lines in the spectrum that we observe. This absorption removes light at specific wavelengths, causing a lack of emission in those areas when we view the Sun's spectrum. The absorption lines allow scientists to analyze the chemical composition and properties of the Sun's atmosphere.