Astronomical distances can be difficult to comprehend. The star nearest to Earth, our Sun, is about 150 million kilometers (93 million miles) away. The next closest star system is about 4 light-years (4 x 10¹³ km or 2.5 x 10¹³ mi) away and the nearest galaxy is about 2 million light-years (2 x 10¹⁹ km or 1.2 x 10¹⁹ mi) away. This interactive resource from the the Harvard Smithsonian Center for Astrophysics illustrates the immense scale of the universe and demonstrates some techniques astronomers use to measure distances.