This month we step back 400 years to Galileo's discovery of the four largest moons of Jupiter – Io, Europa, Ganymede and Callisto – which are collectively known as the Galilean Satellites in their discoverer's honour. Allan Chapman kicks off this month's Focus by telling Galileo's story, before Emily Baldwin profiles each of the four moons, bringing them to life as exciting worlds in their own right. From fiery Io, the most volcanically active body in the Solar System, to Europa, which may host a subsurface ocean with conditions that could support life, the tour then whisks you to the largest of the Solar System's moons Ganymede, and the only moon with its own self-generated magnetic field, and finally on to Callisto, likely the most cratered satellite in the Solar System.

Keeping with the moon theme Ian Welland tells the story of how Saturn's moon Enceladus was discovered by Herschel, and as NASA's Cassini spacecraft prepares to swoop past this enigmatic moon, Michael Caroll looks at what we have learned about the nature of its watery geysers, and interviews Cassini's chief photographer Carolyn Porco. In other features Keith Cooper probes the ferocious jet blasting out of the supermassive black hole lurking in giant elliptical galaxy M87, and we reminisce with our photo diary of AstroFest 2010.

In our regular sections Jeremy Perez shows you how to sketch galaxy clusters, Carole Stott explores the wonders of hot jupiters, Martin Mobberley looks at software that makes planetary imaging that little bit easier, and Nick Howes reviews Meade's latest revolutionary telescope, the six-inch ETX LightSwitch. Plus our new Grassroots astronomy pages for all your society news, our extensive 14-page night sky guide for the month ahead and a news round-up from around the Universe. Plus this month try your luck at winning some great astronomy dvds!