T he Night Sky in July 2024
Venus begins an evening sky appearance in July. At the beginning of the month it sets 30 minutes after the Sun; increasing to 75 minutes by the end of the month. (As Venus sets around 6 pm, it isn’t on the chart.) Venus will be the brilliant ‘evening star’ for the rest of the year. Venus is on the far side of the Sun from us so looks like a tiny, featureless full moon in a telescope. It swings out from the Sun as it catches us up, so will set later. It is 253 million km away mid-month. The Moon will be to the right of Venus on the 7th.
Mercury is also in the evening twilight, fainter than Venus but higher in the sky through July. It sets 80 minutes after the Sun at the beginning of the month and two hours after the Sun at the end. It is 144 million km away mid-month. It looks like a tiny first-quarter moon in a telescope. Around the 25th Mercury will be alongside Regulus, the brightest star in Leo. Mercury will be the brighter of the two. The Moon will be near Mercury on the 8th.
Saturn is up in the late evening. It rises before 11pm at the beginning of the month; before 9 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 midway down the northwest sky. The Moon will be above Saturn on the night of the 24th. By dawn on the 25th the Moon and Saturn will be close together. Saturn is 1360 million km away mid-month. It is worth a look in any telescope but might be fuzzy when low in the sky. The ring can be seen at 20x magnification. Saturn's largest moon, Titan, appears as a star four ring-diameters from the planet.
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 then moves into the southeast sky in the morning hours. It is a 'circumpolar star': seen from NZ it never sets. 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.
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. 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.
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.
Mars rises before 3 a.m. all month. It looks like a reddish star, the same brightness as Saturn. The Moon is near Mars on the morning of the 2nd. Around the 28th Mars will be between Aldebaran and the Matariki/Pleiades star cluster. Aldebaran and Mars will be the same brightness and colour: two orange ‘stars’. Jupiter will be below the orange pair and much brighter.
Jupiter is the brightest ‘star’ in the dawn sky. It rises after 5 a.m. at the beginning of the month. It will then be near orange Aldebaran, the brightest star in Taurus. It rises around 4 a.m. at the end of July. The Moon will be left of Jupiter, and just below Matariki, on the morning of the 3rd, and again on the 31st.
*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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