There is little fundamental difference between "natural" fuels such as wood and fossil fuels such ascoal and oil. Both contain the same combustible substances essential oils and body fats from dead plants and animals.
Answer:
When stargazers go outside at night to look at the sky, they see the light from distant stars, planets, and galaxies. Light is crucial to astronomical discovery. Whether it's from stars or other bright objects, light is something astronomers use all the time. Human eyes "see" (technically, they "detect") visible light.