Serenissimo Principe manuscript with observations of Jupiter's moons

What it is

This is a handwritten manuscript by Galileo Galilei from 1610, beginning 'Serenissimo Principe' (Most Serene Prince). It combines a draft letter offering his telescope for military use with dated notes and small diagrams recording his observations of Jupiter and the four 'stars' moving around it.

Why it matters

The page captures Galileo's discovery as it actually happened, day by day, rather than in the polished form later printed in Sidereus Nuncius. It also shows that Galileo saw practical, even military, value in his telescope — spotting ships and troops — alongside its scientific use, revealing how new science and political patronage were closely linked in his time.

Look closer

• What differences do you notice between this working draft and a finished, printed scientific publication?
• Why would Galileo mention the telescope's military uses when writing to a political leader?
• What do the small star diagrams suggest about how Galileo tracked and recorded changes night by night?