How do astronomers determine which elements are present in a star?

• A. By calculating the mass of the star using its gravitational effects
• B. By observing the brightness of the star over time
• C. By measuring the temperature of the star's surface
• D. By analyzing the emission spectrum of the star and matching the observed spectral lines to known elements

Answer: (D)

Verified step by step guidance

1. Understand that each element emits or absorbs light at specific wavelengths, producing a unique pattern of spectral lines known as its emission or absorption spectrum.
2. Astronomers collect the light from a star using telescopes and pass it through a spectroscope to spread the light into its component wavelengths, creating a spectrum.
3. They observe the positions and intensities of the spectral lines in the star's spectrum, which correspond to the energy transitions of electrons in atoms or ions of elements present in the star.
4. By comparing the observed spectral lines with known reference spectra of elements obtained from laboratory measurements, astronomers can identify which elements are present in the star.
5. This method relies on the principle that each element has a characteristic set of spectral lines, allowing for precise identification without needing to measure other properties like mass or brightness.