A bubble in space: Abell 39 marks the death of a star like the sun. Wind from the aging central star pushes into the surrounding interstellar gas, building up a dense shell that glows blue in this image. After 36 years of travel, the Voyager spacecraft is just now reaching the edge of the sun's own wind-blown bubble.
This is a composite of 25 separate images spanning the period from April 16, 2012, to April 15, 2013. In a video, NASA has also collected three years' worth of such images and set them in a new video.
The planet Venus is seen crossing the sun in June 2004 as photographed through a telescope at Planetarium Urania in Hove, Belgium. The earliest known observation of such a transit was in 1639 by English astronomer Jeremiah Horrocks.
Geert Vanden Wijngaert/AP
Safety over style: In 2006, a Palestinian man and boy were careful to protect their eyes while watching a partial eclipse of the sun. The same cautions are in order for Venus' transit of the sun on Tuesday.
Saif Dahlah /AFP/Getty Images