| | September 17
Mystery Green Blob in Distant Galaxy | | | |
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 | | | A visible-light image of the Fireworks Galaxy, overlaid with data from NASA's NuSTAR X-ray telescope (in blue and green). The mystery green blob is toward the middle of the galaxy, apparently coincident with one of its spiral arms. Image via NASA/JPL-Caltech. | | |
| Mystery green blob in distant galaxy | | The universe is full of mysteries, and now there's a new one for astronomers to puzzle over. NASA's space-based NuSTAR telescope - an X-ray observatory - saw a green blob in the distant galaxy NGC 6946, also known as the Fireworks Galaxy. The blob appeared within a 10-day period and then disappeared again just as quickly. What was it? Read more. | | | What makes a red rainbow? | | | You might see a red rainbow if you're outside at sunrise or sunset, at a time when there's rain in the air. Red rainbows have a surreal beauty, but their explanation is fairly ordinary. They're created via the same physics that makes a sunset or sunrise looks red. Read more and see pictures. | | | | | | | |
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|  | | Tonight … Use Big Dipper to find North Star | | Tonight’s chart shows Polaris and the Big and Little Dippers for a September evening. You can use the Big Dipper to find Polaris, which is also known as the North Star. Notice that a line from the 2 outermost stars in the bowl of the Big Dipper points to Polaris. And notice that Polaris marks the tip of the handle of the Little Dipper. Read more. | | | | | |
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 | | We stand corrected | | Our friend Dr Ski, in Valencia, Philippines, has been looking at images of the sun posted at EarthSky Community Photos, and he gave us a stern talking-to about how to view and photograph the sun safely. Here are his guidelines. In the above photo, Dr Ski said, he “moved the camera a bit to expose just a small portion of the sun's limb to get those cool diffraction spikes (caused by the small aperture blades).” Thank you, Dr Ski! | | |
