Answer:
Betelgeuse is 640 light years away from earth.
Explanation:
A light-year is an astronomical unit to measure the distance the light travels in a calendar year.
If the light from a star takes 640 years to reach us, then that star its 640ly away from us.
Betelgeuse has been labeled as a Variant Star, which means that its brightness can fluctuate over the course of years, this has made difficult for astronomers to measure the exact distance of the star. Right now the star is estimated to be around 613 and 881ly away from earth, although, for the sake of your second question, we will take 640 years as our estimated value.
In 1380 (640 years ago) the Battle of Kulikovo took place. A battle of remarkable importance to Russian history, in which the Russian army, led by Prince Dmitry of Moscow, defeated the Mongol army, defining a turning point in the Mongol dominance, and setting the bases for what Russia is today.
