The Night Sky in July 2025
Mercury makes its best evening sky appearance of the year. At the beginning of the month it appears as a bright star toward the northwest, setting two hours after the Sun. It holds that position till mid-month, slowly fading as more of its sunlit side is turned away from us. It then sinks into the twilight in the third week as it begins to pass between us and the Sun. (Because it sets before 8 p.m. it isn’t on the chart.)
Mars is the only other planet in the evening sky. It looks like a medium-bright red star, setting in the west around 9:40. It is 300 million km away, mid-month, so tiny in a telescope. The Moon will be below Mars on the 28th and above it on the 29th.
Saturn is up in the late evening. It rises around 11:50 at the beginning of the month and before 9:50 at the end (so isn’t on the chart.) It looks like a medium-bright cream-coloured star, due east, all on its own. By dawn Saturn is mid-way up the sky a bit west (left) of due north. The Moon will be near Saturn on the night of the 16th-17th. Saturn is 1370 million km away mid-month. It is worth a look in any telescope. The ring is nearly edge-on to us, so appears as a thin line. Its shadow makes a dark line across the planet. Saturn's larger moons orbit in the same plane as the ring so their shadows are also crossing Saturn. On the night of the 2nd-3rd the shadow of Titan, the largest moon, will be on Saturn when it rises around 11:40. It looks like a small black spot. The shadow moves off the planet around 1 a.m. This repeats on the 18th when Saturn rises around 10:40 and Titan’s shadow moves off just after midnight.
Sirius, the brightest true star, sets in the southwest as twilight ends, twinkling like a diamond. Canopus, the second brightest star, is also in the southwest at dusk. It swings down to the southern skyline before midnight where it also twinkles colourfully. It then moves up into the southeast sky in the morning hours. It is a 'circumpolar star'. Seen from Aotearoa it never sets, except in the most northern places. Canopus is a truly bright star: 13 000 times the sun's brightness and 300 light-years* away.
South of the zenith are 'The Pointers', Beta and Alpha Centauri. They point to Crux, the Southern Cross, on their right. Alpha Centauri is the third brightest star in the sky. It is also the closest of the naked eye stars, 4.3 light-years away. Beta Centauri, like most of the stars in Crux, is a hot blue-giant star hundreds of light-years away. Crux and the Pointers are also circumpolar. They are always somewhere in our southern sky. In summer they are upside down and low in the south.
Midway down the north sky is orange Arcturus. It sets in the northwest around midnight, twinkling red and green as it goes. It is the fourth brightest star and the brightest in the northern hemisphere sky. It is 120 times the sun's brightness and 37 light-years away. It has an orange colour because it is cooler than the Sun; around 4000°C. Above Arcturus is a lone bright star, Spica, the brightest star in Virgo. The Moon will be close to Spica on the 31st. Vega rises in the northeast around 9 pm. It is on the opposite side of the sky to Canopus: low in the north when Canopus is low in the south. Vega is the fifth-brightest star in the sky and the second-brightest northern hemisphere star. It is 52 times brighter than the Sun and 25 light-years away.
The Milky Way is brightest and broadest in the east toward Scorpius and Sagittarius. In a dark sky it can be traced up past the Pointers and Crux, fading toward Sirius. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The thick hub of the galaxy, 30 000 light-years away, is in Sagittarius. The actual centre is hidden by dust clouds in space. A scan along the Milky Way with binoculars shows many clusters of stars and some glowing gas clouds.
Venus rises in the northeast around 4:20 a.m. at the beginning of the month and 5 a.m. at the end, a brilliant object in the dark sky. Golden Jupiter begins a morning sky appearance in July. It rises an hour before the Sun mid-month and at 6 a.m. at the end.
*A light-year (l.y.) is the distance that light travels in one year: nearly 10 million million km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes sunlight four years to reach the nearest star, Alpha Centauri.
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