HERCULES can hardly be described as a striking constellation but it is still fascinating. Many of its stars, like its brightest, Rasalgethi (the lowest in the constellation), are double. Rasalgethi is also one of the biggest stars known, with a diameter 600 times greater than the Sun - if placed in our solar system, it would stretch to Jupiter. This huge red giant, with its blue companion, is a beautiful sight in a small telescope.

But to find the main attraction of Hercules, you don't need a telescope. Take the top "rectangle" of the constellation's shape, and look a third of the way down the right-hand side. If you have clear, transparent skies, you'll see a fuzzy patch. The "blur" is the combined light of about half a million stars, arranged into a tight ball 100 light years across: a globular cluster.

Summer constellations such as Scorpius are putting in an appearance now, and the "Summer Triangle" - Vega, Deneb and Altair - is rising higher in the sky. Red giant Arcturus (meaning "the bear-driver"), the fourth- brightest star in the sky, is highest on June evenings.

Diary for June (all times 24-hour, BST)

2nd 0245 Moon at first quarter

10th 0518 Full Moon

17th 1138 Moon at last quarter

21st 1503 Summer Solstice

24th 0450 New Moon

This column was held over from last week. The Stars column will next appear, as usual, on the last Monday of the month, 29 June.