From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). the spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 485.9 nm. what can we conclude?
- the "star" actually is a planet.
- the star is moving away from us.
- the star is getting colder.
- the star is getting hotter.
- the star is moving toward us.

The star is moving toward us

Explanation:

The wavelength of a distant object changes due to the change in the distance between the observer and the object. This is known as the Doppler effect.

If the wavelength decreases this means that the wavelength in going towards blue which is shorter wavelength. This is known as blue shift. If blue shift occurs then it means that the object is coming closer to the observer.

Hence, the star described here has blue shifted and is moving closer to us.