As NASA's MESSENGER spacecraft arrives in orbit around Mercury this month, we take a look at the journey it has made so far, and some of the targets it has lined up in its sights. As well as interesting surface features, MESSENGER will also probe the planet's tenuous exosphere made of hydrogen, helium and stony and metal particles from the surface, to learn how it interacts with the solar wind. The mission will also complete mapping of the last unknown territories, such as the planet's polar regions.

Elsewhere in this issue, the story of Hanny's Voorwerp is told by its discoverer Hanny van Arkel, alongside the latest Hubble Space Telescope image of that famous green 'blob'; David Powell ventures into the distant past to find out what Earth was like before its calamitous collision with a protoplanet that resulted in the formation of the Moon and changed our world forever, and Martin Mobberley explores the astronomy that can be done between the hours of night and day in the "twilight zone". Meanwhile, Keith Cooper searches for the Sun's siblings – stars that were born in the same nebula as the Sun – which won’t just tell us about our Sun’s birth, but lead to an unravelling of the history of star formation in our whole Galaxy, but discovers that finding those siblings may be harder than we first thought.

With the spring star party season and accompanying Messier marathons upon us, we have observing tips galore, including a tour of the highlights of Messier’s catalogue to find out what these faint fuzzies really are, telescopes that will help you bag those gems, and even a lesson in sketching those objects in a single night, as well as a bumper sky tour of the fertile galaxy hunting territory of Leo.

All this and more, only in the UK's longest running astronomy magazine!