Month’s planets

Jupiter takes pride of place in the dawn sky for early risers, while Mars and Venus grace the twilight

Our Planet of the Month this issue is the largest planet in the Solar System: mighty Jupiter. Between mid-July and mid-August Jupiter will be visible all through the night. Rising in the ESE at around 22:00, looking like a blue-white ‘star’, it will then trace out a low arc across the southern sky during the night, eventually fading from view as the light of the approaching dawn washes it from the western sky.

Though Jupiter will be shining at magnitude -2.7, at this time of year, thanks to summer’s late sunsets and early sunrises, the sky never gets truly dark, so although Jupiter will be an easy naked-eye object, it won’t appear as strikingly bright as that magnitude suggests. It will look noticeably brighter than Saturn, which will be shining to its left all through the summer.

Jupiter is one of the most photographed planets in the Solar System, and it’s easy to understand why. A gas giant world so enormous that our own planet could fit across its disc a dozen times, and so huge that it could contain a thousand Earths, Jupiter has a thick, turbulent atmosphere that churns relentlessly, constantly changing its appearance.

When we look at Jupiter through a small telescope, we can see several horizontal bands of dark clouds crossing its flattened, pale disc. Larger telescopes show more detail, but visiting space probes have given us our clearest views of this amazing world. Today the Juno orbiter is sending back breathtaking images of Jupiter, showing how fierce winds sculpt its multicoloured clouds into ragged streamers and roiling oval-shaped storms.

Jupiter has so many moons – 79 at the last count – that in many ways it’s like a mini solar system orbiting the Sun. The four largest of these moons, discovered by Galileo in 1610, can be seen through just a pair of binoculars as tiny points of light shining close to Jupiter itself, almost lost in the planet’s glare. But you won’t see all four of these ‘Galilean satellites’ every night: the number visible changes from night to night as they whirl around Jupiter, sometimes passing in front of or behind the giant planet.

Constellation: Gemini Magnitude: +0.4 AM/PM: PM

Mercury, the closest planet to the Sun, starts our observing period as a reasonably bright morning star, visible low in the sky before sunrise quite close to Gemini’s most famous star cluster, Messier 35. As the days pass Mercury’s visibility will quickly decrease as it appears to move closer and closer to the Sun, and by the end of July it won’t be observable.

Constellation: Capricornus Magnitude: +0.3 AM/PM: PM

After gracing our morning skies for many months, Saturn is now rising well before midnight, making it an evening object. At the start of our observing period it rises just as the sky starts to darken, followed by brighter Jupiter. After rising it traces out a low arc across the sky, never gaining much height above the horizon before fading from view low in the west at sunrise.

Constellation: Leo Magnitude: -3.9 AM/PM: PM

Venus will be an evening star during our observing period, appearing as a spark of light low in the west after sunset. Look closely at it as twilight deepens on 15 July and you’ll see a fainter ‘star’ very close to it on its lower right. This is Mars, and the two worlds will be less than one-and-a-half degrees – or three Moon widths – apart, looking beautiful together.

Constellation: Leo

Magnitude: +1.8

AM/PM: PM

Mars is an evening object at the start of our observing period, but shining at only magnitude +1.8 – approximately as bright as Polaris, the Pole Star – it will be quite hard to see in the bright twilight sky, and will be a little harder to see each night as it drifts towards the Sun. However, in mid-July the Red Planet will be in the same binocular field of view as much brighter and more obvious Venus, which will make it easy to find: on the evening of 15

July they will be just under one-and-ahalf degrees apart, and will look great through binoculars or small telescopes.

Constellation: Aries Magnitude: +5.9 AM/PM: AM

Uranus is a morning object through June and into July, a little higher in the sky and farther away from the Sun each morning. At magnitude +5.9 Uranus would be a naked-eye object for many under a dark sky, but with the sky in June and July never growing truly dark, it’s likely Uranus’ faint light will be overwhelmed, and you’ll need a pair of binoculars to find it.