自美国革命以来，这颗恒星的光芒就一直在穿越太空。以下是如何找到它

The United States' 250th birthday is right around the corner and what better way to celebrate than by looking for a star whose light began its journey to Earth around the time the Declaration of Independence was signed?

Starlight travels through the near-perfect vacuum of space at a staggering 186,282 miles (299,791 kilometers) per second— or the speed of light. Even at this pace, it can take hundreds, thousands, or even millions of years for starlight to reach its destination, rendering each point of light in the night sky a twinkling time capsule, which represents a snapshot in the life of a star encoded at the moment the radiation left its source.

蓝白色双星系统处女座阿尔法星（俗称角宿一）恰好在距离地球约 250 光年的地方发光。 In other words, the light we see today left the star's surface 250 years ago, around the time that America's founding fathers signed the Declaration of Independence in 1776.

How to find Spica in the night sky

Finding Spica is easy. First, locate the Big Dipper, shining above the northwestern horizon in the hours following sunset in June for viewers in the U.S., with the three stars representing its "handle" pointing up and away from the horizon.

Next, draw an imaginary line following the arc of the handle out into space, until you find the red light of Arcturus, the 4th brightest star in the night sky. Continue the arc beyond Arcturus and the next dazzling bright blue-white star that you spot will be Spica, which twinkles above the southwestern horizon at sunset in early summer.

The single point of light that we call Spica is actually a pair of massive stars that orbit each other once every four days, while shining with the combined light of over 12,000 suns.

Want to get a closer look at the night sky? Then be sure to read our roundup of the best telescopes and binoculars for exploring the post sunset realm, along with our beginner's guide to amateur astronomy.