To complete my imaging session, I captured the Great Globular Cluster in Hercules (Messier 13), which was getting higher in the sky after midnight. Its apparent magnitude is 5.8 and can be spotted with the naked eye under a dark sky.
Located 25,000 light-years from Earth, it was discovered in 1713 by the English astronomer Edmond Halley (known because he recognized the periodicity of the comet that has his name). It’s home of over 100,000 stars!
Fun fact: On November 16, 1974 the Arecibo radiotelescope sent a message at the current location of M13, to potential extraterrestrial civilizations.
From Wikipedia: “The Arecibo message is an interstellar radio message carrying basic information about humanity and Earth that was sent to globular star cluster M13 in 1974. It was meant as a demonstration of human technological achievement, rather than a real attempt to enter into a conversation with extraterrestrials“. The message will take 25,000 years to get there, and we will have to wait 25,000 years to get a potential response!
Since Messier 13 is a very bright object, I had to take several short exposures (10 seconds) as long exposures could blow up the bright stars. The total integration time for Messier 13 was 11 minutes and 20 seconds (68×10 secs., dark, flat, bias).
When I processed the image with PixInsight, I noticed that I captured a distant spiral galaxy (IC4617), 489 million light years distant. Light has traveled almost half a billion years from this distant galaxy to reach our eyes!
Note: Scroll the slider to switch between the images of M13 with and without annotation.