In August, we already feel the days getting considerably shorter. On the 1st, the sun set around 8:45 p.m. in mainland Portugal, but on the 31st, it set around 8:00 p.m.
It also affects the visibility of planets. On the 1st, the planet Saturn was born shortly after nightfall, around 9:30 p.m., but at the end of the month, it is already visible as soon as the Sun passes below the horizon. But during the month of August, we will have the opportunity to see the 5 planets visible to the naked eye.
Mercury has just left the direction of the Sun and begins to see itself at dusk. The best time to see it will be between the 13th and the 19th. Despite everything, this planet will be at a maximum of 10 degrees above the horizon (the outstretched arm, this more or less corresponds to the space occupied by a clenched fist) and be visible only between half an hour and 45 minutes. To increase the chances of seeing Mercury, it is recommended to do so in places with the horizon facing west without any hindrance.
Jupiter and Mars won’t be visible at dusk, but as the month progresses they rise earlier and earlier. The largest planet in the solar system was born at 11:15 p.m. on the 1st, but will be visible at 9:15 p.m. on the 31st. Mars follows suit, although a bit more slowly, being visible at 1:15 a.m. on the 1st, and around midnight on the 31st.
As for Venus, it is already approaching the Sun – it was born around 05:00 on the 1st and at 06:00 on the 31st.
The Moon, which moves a little less than a hand a day across the sky, was crescent on the 5th. A week later, on the 12th, it reached the full moon phase and passed just 5 degrees from Saturn.
Unfortunately, this is also the day when the Perseid meteor shower, one of the biggest “star showers” of the year, peaks. So while this shower typically has up to 100 visible meteors per hour (in dark skies), the moon’s brightness is expected to cut that number in half.
In cities, due to light pollution, the number of visible meteors is about 10% of the number expected in dark skies, i.e. only 5 should be visible per hour. But it’s not all bad news, as the Perseids are rich in “fireballs” (bigger, brighter meteors), so it should be worth spending an hour staring at the sky.
On the 14th, Saturn reaches opposition, which means the Sun, Earth and Saturn will be aligned, with Saturn on the opposite side of the sky from the Sun.
On August 15, the start of the holidays for some and the end for others, Mercury will be at its highest point at dusk, and a few hours later the Moon passes 6 degrees from Jupiter. On the 19th, the day the Moon reaches the waning phase, it passes 3 degrees Mars.
We will then have to wait until the 25th, when our satellite, in very fine decrease, passes 7 degrees from Venus, just before dawn. The 27th is the day of the new moon and on the 29th we have the observation challenge of the month: A very thin crescent Moon will be 4 degrees from Mercury, but the planet is already approaching the Sun, in the sky, and it should be visible for less than half an hour, just after sunset.
Author: Ricardo Cardoso Reis (Porto Planetarium and Institute of Astrophysics and Space Sciences)