SkyMatters: Use the Moon to help find three planets in July

The problem with planets is that they move.

If someone asks you where Venus or Mars will be tonight, or in a month’s time, unless you’re extremely familiar with the sky almanac (or have one of the many apps for your mobile device that show what’s in the sky) it is highly unlikely that you’ll know the answer.

If you do know the answer for this year, there’s no guarantee that it will be the same for next year. In fact, it almost certainly will not! This is very different to stars, or the constellations they make up.

If you know, for example, that the constellation Lyra will be visible in July in 2017 (which it is) you can be sure it will be visible at the same time next year.

However, if Venus is a morning object in July 2017 (which it is) it does not necessarily follow that it will be so in July 2018. The word ‘planet’ comes from the Greek for ‘wanderer’, precisely for this reason.

You can use the Moon to help find three planets in July. On the 6th an almost-full Moon will appear to the top right of the planet Saturn and although the brightness of the Moon will make it slightly challenging to see the giant ringed planet, Saturn should be sufficiently bright to be discernible.

And once you know where Saturn is you can keep an eye on it from night to night.

You will notice that within a couple of nights the Moon will have moved well away from Saturn and will no longer interfere with your viewing.

This movement of the Moon reflects the fact that it is in orbit around the Earth. If you have binoculars or a small telescope you should be able to see Saturn’s rings which are rather favourably oriented this year.

Seeing Saturn’s rings is truly one of nature’s greatest spectacles and it’s not even cold outside at night, so there’s no excuse for not trying!

On July 20, in the early hours of the morning around 4:30am a thin sliver Moon will sit between Venus to the left and the giant star Aldebaran to the right.

This should make for an amazing sight. Venus should appear bright and pale-yellow. It will almost certainly not twinkle.

Aldebaran will appear red and is very likely to twinkle (which is common for stars, particularly near the horizon).

On July 28, in the evening sky, the Moon will appear above the planet Jupiter at a distance of about three Moon diameters. The Moon will be 30% illuminated and Jupiter will be easily seen.

And if you do head out to look for planets, be aware that the Delta Aquarids meteor shower peaks in the early hours of July 30.

While not a spectacular shower, it is unusual in that it appears to come from the debris left behind by two sun-grazing comets, Marsden and Kracht, which were ripped apart by the gravitational interaction as they rounded close to the Sun.

As always, the best way to look for meteors is with the naked eye.

And remember that the better your eyes have adapted to the dark the more the likelihood is that you will see fainter meteors.

Did you know?

There are over 50 events for the public as part of a Summer of Space, an initiative between Blackrock Castle Observatory and the International Space University.

All events are free, but many need to be booked online at


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