- M 25 (IC 4725)
M 25 is an open cluster located within the stream of the Milky Way in Sagittarius close to the nebulas M 16 and M 17. Like these other objects, M 25 was originally discovered by the Swiss astronomer Phillippe Loys de Cheseaux in 1745 or 1746. It was independently discovered by Messier in 1764. The English astronomers William and John Herscell did not observe M 25, which is why it does not have an NGC number.
M 25 contains around 220 member stars. The brightest star, U Sagittarii, is a classical Cepheid variable with a magnitude that varies from 6.3 to 7.1 over a period of 6.75 days. This is the bright orange-ish star close to the center of the cluster in my image. The cluster is located at a distance of around 2020 LY, which puts it between our local spiral arm (Orion-Cygnus arm) and the Sagittarius arm in our galaxy. This object is easily seen in 10 × 50 binoculars, where it appears as a bright patch of light along the course of the Milky Way.
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