Astronomical Distances
The light year and the astronomical unit
"The closest star to the Sun, Alfa Centauro, is located at a distance of 40,661,440,000 km. But most of the stars are further away, for example; Vega is about 240 billion km, Rigel about 8,600 billion, and the distance in km to a group of stars in the constellation Ursa Major is a six followed by twenty-one zeros".
The distances indicated in the previous text are so great that they become difficult to handle. For this reason, the unit of length called light year was created to express astronomical distances.
- Light Year: It is the distance that the light travels in a terrestrial year.
The speed of light in the vacuum is 299 792, 458 km per second, that is, approximately 300,000 km per second.
To convert a light year in km, we can multiply 300,000 km / s by 31 536 000 s, which is the number of seconds in a year:
1 light year = 300 000 km / s * 31 536 000 s = 9 460 800 000 000 km (approximately 10 billion kilometers).
To convert distances expressed in light years into kilometers, we multiply the number of light years by 10 billion. To do it in a simple way, we add thirteen zeros.
For example, the distance between the Earth and Antares is 520 light years = 5,200,000,000,000,000 km.
Distances in the solar system
The distances between the celestial bodies of the solar system are very large but much smaller than those between the stars. For the distances between celestial bodies that are very large to express them in km, but small to express them in light years, the astronomical measure (AU) is used where 1 AU = 149 600 000 km (distance measured between the Earth and the Sun).
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