June and July are the best times each year to look for noctilucent clouds in the north. These strange ‘night-glowing’ clouds have been reported since the mid-19th century, and appear to be formed of ice crystals reflecting sunlight from below the horizon, but the air should be too thin at their height to support ice crystals, let alone have winds strong enough to move them like cirrus clouds at lower levels.
The Moon will be Full on July 13th, which will be a Supermoon, at Full when at its nearest to Earth (perigee). The Moon was New on June 29th, and will be again on July 28th. There’s more mystery about the object which struck the lunar Farside on 4th March. It appeared to be a discarded rocket stage, and a Chinese one at that, probably from the Chang’e 5-T1 mission of 2014. But China’s experts insist that vehicle returned to Earth and was destroyed in the atmosphere. Now the impact site on the rim of Hertzsprung crater has been photographed by Lunar Reconnaissance Orbiter, and it’s clearly a double crater, as if the impactor had a large mass at each end, unusual for an empty rocket body. ‘Curioser and curioser’!
In late June there was a line-up of the naked-eye planets, east to west in order from the Sun, which won’t be seen again until 2040. Mercury was rising at 3.30 a.m., an hour before the Sun, but as that’s close to full daylight in Scotland at this time of year, there was little chance of seeing it and searching for it could be dangerous, with the Sun so close below the horizon. Mercury disappeared from the morning sky before June ended, is at superior conjunction on the far side of the Sun on July 16th, and is not visible in July, August or September. However Venus, Mars, Jupiter and Saturn are all visible at some time during the night and are joined now by Uranus and Neptune, though you need telescopes to see those.
Venus is brilliant in the morning sky, rising at 3 a.m. in July. The waning crescent Moon is near Venus on July 26th and 27th.
Mars is in Pisces, and rises at 00.30 a.m. in July, moving into Aries on July 9th. The Moon is nearby on July 21st, and will occult Mars as seen from Japan and north-east Russia. Mars draws close to Uranus at the end of the month, closest together on August 1st.
Jupiter rises at midnight in July, in Pisces, and will soon make a welcome return to our maps along with Neptune and Saturn. Jupiter is near the Moon on July 19th. Jupiter comes to its ‘stationary point’ on July 29th, pausing and then reversing its general eastward motion against the stars as it’s overtaken by the Earth. On July 14th, the icy moon Europa will emerge from the shadow of the planet between 2.47 and 2.51 a.m., only to disappear behind the planet itself five minutes later.
Saturn in Capricornus rises at 10.30 p.m. in July. The Moon is near Saturn on July 15th.
Uranus in Aries rises at 1 a.m. in July, and is near the Moon on the 22nd, near Mars at the end of July.
Neptune in Aquarius rises at 11.30 p.m. in July, and is near the Moon on the 18th.
The Tau Herculid meteors, which might have generated a spectacular shower or even a ‘storm’ at the beginning of June, did indeed make an appearance, though it wasn’t spectacular even in parts of the world where the sky was dark – from which Scotland was well and truly excluded. For us, the next major meteor shower would be the Perseids in mid-August, but this year their peak coincides with the Full Moon. The Southern Delta Aquarid shower peaked on July 28th, with little problem from the New Moon, but because the radiant is so far south not much could be expected from here.
Meanwhile there’s growing interest in the evolving dust trail from Comet 17P Holmes, named after the astronomer who first noticed it in 1892 while observing the Great Nebula in Andromeda. It’s a short-period comet, captured by Jupiter into a relatively tight orbit taking 6.88 years, between 2 and 5 times the Earth’s distance from the Sun, made visible by outbursts of dust in 1892 and 1893. Nothing was happening when it was relocated in 1964 and by the Hubble Space Telescope in 1999, but although its nucleus is only 3.4 km across, in 2007 it produced a dust cloud which was larger than the Sun. A blue ion tail showed there were also ices present. As the dust trail spread, it was thick enough to be photographed in 2015, and the particles are now converging on the far side of the Sun from the comet, where they may become visible even with small telescopes during late July and August. The comet itself won’t pass the Earth again until 2028. Even then it will be well beyond the orbit of Mars and no meteors are expected to reach Earth, but a meteor trail has never been observed directly before, and the way this one is evolving is of great interest to meteoriticists. (I had to get that word in somewhere!)
Duncan Lunan’s most recent books, From the Moon to the Stars and The Other Side of the Interface, were published by Other Side Books in 2019 and 2021, and are available through Amazon or through bookshops, or from the publishers. For details and for his other books see Duncan’s website, www.duncanlunan.com
You can download a copy of July’s star Map here:
Categories: Science
