This month we have already been able to see some planets at “decent” times. Venus is visible at dusk – it is that “evening star” that can be seen just after sunset, low on the horizon, facing West.
Saturn begins the month to rise at around 22:30 pm, but on the 31st it can be seen, facing East, just after the Sun sets.
Jupiter and Mars continue to be visible only at dawn, but their apparent movements are very different, with the two planets crossing each other.
At the beginning of the month, Jupiter rises at around 02:30 am, but, at the end, it is seen at around 00:45 am.
As for Mars, at the beginning of the month it rises before Jupiter, at around 02:00, but on the 31st it rises later, at around 01:15.
And to start the month, there's nothing like a starting Moon – on the 4th, our natural satellite reaches the new moon phase. Just one day later, a very thin crescent of the Moon passes less than 2 degrees from Venus, just after sunset.
However, you won't have much time to observe them, because although the Sun passes below the horizon at around 20:45 pm, the Moon/Venus pair disappears around 21:30 pm.
On the 12th, the Perseid meteor “shower” peaks. These occur when the Earth passes through the trail of dust left by the passage of comet Swift-Tuttle, which has a nucleus 26 kilometers in diameter (by comparison, the meteorite that caused the extinction of the dinosaurs would be “only” 12 km).
This comet, which has an orbit of about 133 years, passed close to Earth in 1992 and will return in 2126.
This is not the best year to observe the Perseids, as the peak of this “rain” is expected to occur during the day. However, the Moon sets at more or less the same time as the radiant (the point from which the meteors appear to emanate), the constellation of Perseus, is rising, and the number of meteors gradually increases until the maximum.
So, on the night of the 11th to the 12th, turn east after 23:30 pm and look up, watching the meteors pass by.
On the 15th, the planets Mars and Jupiter will cross paths in the sky. These rise at around 01:45 and will be separated by just 20 arc minutes – this separation corresponds more or less to the thickness of two 20 cent coins, at arm's length. They are then observable until dawn, around 06:30 am.
The 19th is the night of the full moon and two days later, on the 21st, you will be able to observe an occultation of Saturn by the Moon. Our satellite begins to cover the planet at around 04:11 in Faro, 04:13 am in Coimbra, around 4:14 am in Porto and 04:16 am in Bragança.
In Madeira it starts at around 03:49, while in the Azores, it depends on the group: it starts between 02:55 (local time) in Santa Maria and 03:02 in Flores. The occultation lasts for around 1h10min, with the planet reappearing on the opposite side, for example in Porto, at around 5:19am.
On the 26th, the Moon reaches its waning quarter. Our satellite passes about 6 degrees from Jupiter on the 27th and 4 degrees from Mars on the 28th.
Good observations and, if applicable, happy holidays!
Author Ricardo Cardoso Reis (Porto Planetarium and Institute of Astrophysics and Space Sciences)
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