The top sights to observe or image this month
Don’t miss: Thin Moons and planets
BEST TIME TO SEE: 15/16, 17/18, 19, 21, 26 and 27 July at times specified
The Moon circumnavigates the night sky once every 27.321 days, never straying far from the ecliptic. The main planets in the Solar System also tend to remain close to the ecliptic and consequently, the Moon makes a pass of each one every month.
This month’s encounters are in the morning sky with Saturn up first. Approaching opposition on 14 August, Saturn is currently in eastern Capricornus. It encounters a 92%-lit waning gibbous Moon on 15/16 July, the Moon passing 5˚ south of the planet. On the night of 17/18 July it’s Neptune’s turn, although this dim mag. +7.9 planet will be tricky to see against the light from a 76%-lit waning gibbous Moon, which lies 4.2˚ to its south.
There’s no problem spotting Jupiter near the Moon on the morning of 19 July. Shining at mag. –2.4, the gas giant appears 2.8˚ north of the Moon’s centre at 03:30 BST (02:30 UT) on 19 July. If the day ahead is clear, try and stick with the pair after sunrise. They are due south at 06:00 BST (05:00 UT) with an altitude of 35˚.
Mars is next and its encounter gives a tantalising taste for what’s to come later in the year. On the morning of 21 July Mars lies in the Moon’s direct path, 6.2˚ to the west. As the day progresses, the gap reduces so that by the time they are approaching their setting point, they will be just 2˚ apart. Shining at mag. +0.3, Mars will be a tricky daylight target. If there were no horizon, we’d see the Red Planet miss the Moon’s southern edge by just 3 arcminutes from the UK’s centre, even closer from the extreme north of the country. There will be a series of close lunar passes with Mars over the coming months, and the Red Planet will be occulted by a full Moon on 8 December.
The 35%-lit Moon remains close to Mars on the morning of 22 July and even closer to Uranus on this date, 1.9˚ from the dimmer planet at 03:15 BST (02:15 UT). Uranus appears 22 arcminutes north of the Moon’s centre at 07:20 BST (06:20 UT), but at mag. +5.8 under daylight conditions is out of reach. It’ll be interesting to try and record it using an infrared sensitive camera at this time, to see whether this is possible.
Finally, on 26 July the 6%-lit waning crescent Moon lies 5.8˚ northwest of Venus, while on the morning of 27 July, the now 2%-lit waning crescent lies 6.8˚ to the northeast of Venus. The pair rise above the northeast horizon approximately 80 minutes before sunrise.
Southern Delta Aquariids meteor shower
BEST TIME TO SEE: 28–31 July, midnight BST (23:00 UT) through to 03:00 BST (02:00 UT)
The Southern Delta Aquariids meteor shower peaks on 28–29 July. This year the Moon will be absent from the sky, as it approaches the new phase on the afternoon of 28 July. This leaves the sky dark for Southern Delta meteors. Well, when we say dark, we mean as dark as it ever gets at the end of July! For those in the north of the UK, the sky still carries its characteristic deep blue colour, never reaching proper astronomical darkness at all. Even from the far south of the UK, proper darkness is rather brief.
Don’t let this detract you from enjoying the shower though, as bright trails will make themselves known. The Southern Delta Aquariids (SDA) shower is active between 12 July and 23 August, reaching peak activity at the end of July, on the nights of 28/29, 29/30 and 30/31 July. It’s well worth observing across all three dates if you can. Peak rates typically reach a zenithal hourly rate (ZHR) of 16 meteors per hour but, as we often state in the ‘Sky Guide’, ZHRs can be misleading. The ZHR figure represents the number of meteors expected to be seen per hour under perfect viewing conditions with the shower radiant – the region of sky where the shower meteors emanate from – directly above your head. Such conditions are rarely met and this is the case with the SDA, its radiant sited near Skat (Delta (γ) Aquarii), which doesn’t get very high from the UK.
To observe the shower, find somewhere dark and sit or lie back, looking up at the sky; an altitude of 60˚ (two-thirds up from the horizon) is ideal, in any direction. As the nights are short in July, an all-night watch still allows you to get some sleep after the session.
Noctilucent clouds season – part 2
BEST TIME TO SEE: 90–120 minutes after sunset, or at similar time before sunrise
June and July are the best months for spotting elusive noctilucent or nightshining clouds. These are a phenomenon which bridge the divide between space and weather, occurring at an altitude of 82km in the mesosphere. NLCs form as sheets of tiny ice particles, seeded by fragments of meteor dust, the tiny remnants left behind when a meteoroid vaporises in Earth’s atmosphere. The temperature of this region of the mesosphere becomes super-cooled in the Northern Hemisphere during its summer, the tiny pieces of meteor dust acting as nuclei for the ice crystals that eventually spread into an NLC sheet.
If present, NLCs are typically seen 90–120 minutes after sunset, low above the northwest horizon, or a similar time low above the northeast horizon before sunrise. Big displays may persist all through the night, moving through north as they track the position of the Sun beneath the horizon.
As they reflect sunlight, NLCs appear bright against the twilight sky, taking on their characteristic attribute of shining at night. Their appearance is distinctive, often exhibiting an electric blue colouration and with fine stranded or herringbone structures. As they sometimes appear bright, they also make superb targets for cameras and may be recorded using modern smartphones.