The sun ejects a mid-level flare, rated M6.5, on April 2. NASA's Solar Dynamics Observatory captured the event in two wavelengths of extreme ultraviolet light.

M-class flares are a tenth as powerful as X-class events, the most intense flares our sun spits out. The flare also created a coronal mass ejection, which occurs when the sun belches a plume of superheated gas. A flare aimed directly at Earth can cause significant damage to electrical systems and satellites. (See "Solar Flare: What if Biggest Known Sun Storm Hit Today?")

View Images Photograph by European Southern Observatory

Released on April 2 by the La Silla Observatory in Chile, this composite image of two galaxies reveals two very different life histories. The small spiral galaxy on the right, NGC 1317, has led a relatively peaceful life.

But its larger companion on the left, NGC 1316, bears scars from a violent past. Dust lanes embedded in a matrix of stars suggest that it gobbled up a spiral galaxy about three billion years ago. It has also ripped stars from their moorings and flung them into interstellar space, as evidenced by faint tidal tails—wisps of star matter that trail or precede a galaxy. (Get a closer look at NGC 1316's dust lanes.)

View Images PHOTOGRAPH BY BABAK TAFRESHI, ESO/TWAN

The Milky Way galaxy lights up the night above two ALMA radio telescopes in Chile's Atacama Desert. The altitude—16,400 feet (5,000 meters) above sea level—allows for exceptional visibility. The image was submitted to "The World at Night" by photographer Babak Tafreshi on April 1.

The Southern Cross constellation is visible to the left of the radio telescope in the foreground; Saturn is the brightest orb of light halfway down the image to the right.

View Images Photograph by Daniel J. H. McDonald, National Geographic Your Shot

The surface of the moon is pockmarked with craters, punched by ancient collisions with asteroids or comets, in this image submitted to YourShot by Daniel McDonald on April 3.

View Images Photograph by NASA, ESA, J. Jee (Univ. of California, Davis), J. Hughes (Rutgers Univ.), F. Menanteau (Rutgers Univ. & Univ. of Illinois, Urbana-Champaign), C. Sifon (Leiden Obs.), R. Mandelbum (Carnegie Mellon Univ.), L. Barrientos (Univ. Catolica de Chile), and K. Ng (Univ. of California, Davis)

A composite image released on April 3 combines x-ray data from the Chandra Observatory and optical data from the Hubble Space Telescope to form this brightly colored image of the galaxy cluster El Gordo—"the fat one" in Spanish. Information gathered from Hubble observations indicates El Gordo may be three million billion times the mass of our sun, or about 43 percent larger than researchers had thought.

The galaxy cluster, first discovered in 2012, is about seven billion light-years from Earth and is the most massive known galaxy cluster at that distance or beyond. Researchers think most of its mass is tied up as dark matter, colored blue in the image above.

View Images PHOTOGRAPH BY P-M Hedén, TWAN