- Planétarium Rio Tinto Alcan
From July 30 to August 13, 2018
In August, four planets are visible at twilight between the west and southeast. Appearing from right to left are Venus, Jupiter, Saturn and Mars. The Moon is also part of the scene from the 13th to 23rd; on August 14, the crescent Moon hangs a few degrees above Venus. Catch all five in a single viewing about 40 minutes after sunset in the colourful twilight sky; Venus is the first to sink below the horizon soon thereafter.
Mercury is presently too close to the Sun and is not observable. The tiny planet passes between Earth and the Sun (inferior conjunction) on August 8 and gradually reappears at dawn a couple of weeks later.
Venus is the bright Evening Star that pierces through the colours of twilight in the west, as soon as the sky begins to darken minutes after sunset. Venus is still pulling away from the Sun, but its orbit is tilting down on the horizon: as a consequence, Venus now sets less than two hours after our daytime star. At dusk on August 14, the lunar crescent hangs 6 degrees above Venus: with binoculars, admire the earthshine that dimly lights the otherwise dark section of the lunar disc. The scene becomes truly magnificent when the sky darkens, 30 to 45 minutes after sunset.
Mars was at opposition on July 27, which means it’s presently closer to Earth, larger and brighter than at any time in the past 15 years; for a few weeks, it even outshines bright Jupiter. Mars appears low in the southeast at dusk, culminates just after midnight barely 18 degrees high in the south, and vanishes in the southwest at dawn. Mars is presently performing its retrograde loop: until late August, it is moving westward (toward the right) with respect to the background stars. During the night of August 22 to 23 and 23 to 24, the waxing gibbous moon will shine near the Red Planet.
Jupiter appears above the southwest horizon during evening twilight and spends the rest of the evening slowly descending toward the west-southwest horizon where it vanishes before midnight. The waxing Moon will appear near Jupiter on the evenings of August 16 and 17.
Saturn appears during evening twilight above the south-southeast horizon, culminates around 10 p.m. about 22 degrees high in the south, and then gradually descends toward the southwest horizon where it vanishes after 1 a.m. During the night of August 20 to 21, the waxing gibbous moon shines a few degrees to the right of the ringed planet.