The Evening Sky in July 2017

Download a PDF containing this chart, additional charts for specific areas of the sky and descriptions of interesting objects visible at this time of year.

The Evening Sky in July 2017

Golden Jupiter is the bright 'evening star' appearing in the northwest sky soon after sunset. Above it is bluish Spica. Orange Arcturus is midway down the north sky. Cream-coloured Saturn is northeast of the zenith with orange Antares, somewhat fainter, above it. Sirius, the brightest star but fainter than Jupiter, 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 south later. South of the zenith are 'The Pointers', Beta and Alpha Centauri. They point to Crux the Southern Cross on their right. Vega rises in the northeast around 9 pm.

Mercury (not shown on the chart) begins an evening sky appearance early in the month, setting steadily later. In the first week of July it is in the northwest, setting an hour after the sun. By the end of the month it sets at 8 p.m. a little north of due west. Mercury, Regulus and the Moon will be close together on the 25th.

Any telescope will show the oval disk of Jupiter with its four 'Galilean' moons lined up on either side. Larger telescopes show dark stripes parallel to Jupiter's equator. These are caused by temperature differences in the clouds. Jupiter is 820 million km from us mid-month. The Moon is near Jupiter on the 1st and the 29th. Jupiter sets around 1 a.m. at the beginning of the month, reducing to 11 p.m. by the end.

Saturn is always worth a look in any telescope. A small telescope shows Saturn's ring, now at its greatest tilt. Saturn's biggest moon Titan looks like a star about four ring-diameters from the planet. Larger telescopes show smaller moons as faint stars closer to the rings. Saturn is around 1370 million km away in July. It sets in the southwest near dawn. The Moon is near Saturn on the 7th.

Alpha Centauri is the third brightest star. 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 blue-giant star hundreds of light years away. Canopus swings down to the southern skyline before midnight then moves into the southeast sky in the morning hours. It is a 'circumpolar star': it never sets. Crux and the Pointers are also circumpolar. Canopus is a truly bright star: 13 000 times the sun's brightness and 300 light years away.

Arcturus, in the north, 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 twinkles red and green when setting in the northwest around midnight. It is an orange colour because it is cooler than the sun; around 4000°C.

East of the zenith is the orange star Antares, marking the body of the Scorpion. The Scorpion's tail, upside down, is stretched out to the right of Antares making the 'fish-hook of Maui' in Maori star lore. Antares is a red giant star: 600 light years away and 19 000 times brighter than the sun. Below Scorpius is 'the teapot' made by the brightest stars of Sagittarius. It is also upside down in our southern hemisphere view.

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.

The Large and Small Clouds of Magellan, LMC and SMC, look like two misty patches of light low in the southern sky. They are easily seen by eye on a dark moonless night. They are galaxies like our Milky Way, but much smaller. The Large Cloud is 160 000 light years away and 5% of the mass of the Milky Way. That is still many billions of stars. The Small Cloud is 200 000 light years and 3% of the Milky Way's mass.

Brilliant Venus rises in the northeast after 4 a.m. At the beginning of the month it is above the Pleiades/Matariki star cluster with orange Aldebaran to the right of the cluster. The stars creep higher in the sky through the month while Venus sinks lower. It is between Matariki and Aldebaran around the 11th.

*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes four years for sunlight to reach the nearest star, Alpha Centauri.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
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