To measure the vast distance in space ,scientists use a unit called a _, which is how far travels in one year. The closest star to Earth is _.

(Look at the picture)

light-year; the sun

Explanation:

A light-year is the distance light travels in one year. This means that a light-year is a measure of distance, and is useful on a larger scale because of its large size (light travels a pretty big distance in a year!), so light-years are used by scientists to measure the vast distance in space.

The closest star to the Earth is the Sun.

Gravity is the natural phenomenon in which all objects with mass are attracted to (or gravitate towards) one another. Since gravity is neither a measure of distance nor a star, it doesn't fit any of the answer blanks.

Light is the portion of the spectrum of electromagnetic radiation that is visible to the human eye (between infrared and ultraviolet wavelengths). Since light is neither a measure of distance nor a star, it doesn't fit any of the answer blanks.

A megameter is an instrument for determining longitude by observation of the stars. Since a megameter is neither a measure of distance nor a star, it doesn't fit any of the answer blanks.

Betelguese is a star that is part of the Orion, notable because of its brightness and size, as well as the fact that it is likely to become a supernova in less than a million years. While Betelguese is a star, it isn't the closest star to the Earth. Therefore, it doesn't fit any of the answer blanks.

Hope this helps! :)