July is probably my favourite month for observing the stars. As nights gradually get longer, evenings provide relief from frequent summer heat waves. Summer’s humidity gives the stars a diffuse air, and the aroma of the countryside creates a magical atmosphere. Far from the city, when the humidity dissipates, moonless nights reveal a breath-taking sight: the Milky Way stretching across the sky.
Stars by the billion
Summer’s back, and with it so is the Milky Way. That milky-white glow stretching overhead is our galaxy. But what exactly is a galaxy? If all the stars in the sky were houses, then galaxies would be cities. Our celestial city is the Milky Way, and the Sun is one of 200 billion stars that constitute it. The Milky Way is shaped like a flat disk; the Sun is somewhere between the edge and the centre.
In summer, Earth’s position with respect to the Sun is such that our night side faces the centre of the Galaxy (downtown); in winter we face toward the outside (the suburbs). That’s why the summer sky affords a view of billions of stars concentrated in our galaxy’s central regions and along its disk. Because they’re so far away, we can’t distinguish these stars individually, but their combined light produces the glowing white band that arches across the sky. But our galactic city contains more than stars; there’s also a lot of interstellar dust that absorbs light. This dust appears like dark lanes silhouetted against the brighter parts of the Milky Way. If you scan these regions with binoculars or a telescope, you can imagine all the stars, nebulae and exoplanets that lie hidden there…
A lengthy meteor shower
July is also a great month for observing shooting stars. Whenever the subject comes up we usually think of the August Perseids, but there’s another noteworthy meteor shower, the Delta Aquarids, which begins around mid-July and lasts for nearly a month! The new moon, on the 26th, will offer excellent observing conditions since it coincides with the shower’s maximum. During this peak period, over 10 meteors per hour should easily be visible. The Delta Aquarids are most active after midnight: Scan the sky in all directions and keep your eyes peeled.
The first week of July is your last chance to see Jupiter early in the evening; after that, the giant planet disappears in the Sun’s glare and will re-emerge at dawn, in August. Mars, the Red Planet, is in Virgo; Saturn, the ringed planet, is in Libra. Both can be easily seen from early evening to midnight. On July 13, Mars will pass 1.4° north of the bright star, Spica.
Mercury and Venus are presently in Taurus and are visible at dawn, just before sunrise. Dazzling Venus is easy to find above the eastern horizon. Mercury orbits closer to the Sun and is harder to spot, but from July 12 to 20, conditions will be favourable: Look for the tiny planet just to the lower left of Venus.
The Moon will be full during the night of July 11 to 12, and new on the 26th. On the evening of July 5, the Moon will be just half-a-degree (the diameter of the lunar disk) to the south of Mars — a splendid encounter! Two evenings later, on the 7th, it will pass slightly farther from Saturn. On the 24th, a very thin, waning lunar crescent will appear to the right of brilliant Venus; yet another splendid sight!
Make the most of warm summer days and the magnificent night-time sky. And don’t forget to prepare your wish-list for the shooting stars at the end of July!