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We had not seen Mars since July. From the first days of November, Mars can be seen just before dawn, very low in the east. During the sunsets this weekend we can also see a beautiful conjunction between Venus, Jupiter and Saturn with the thin edge of the crescent moon.

Outer planet

The size of Mars is approximately half that of the Earth, but its rotation period and seasonal cycles are very similar to those of our planet. However, being farther from the Sun, its average temperature is much lower than the Earth's, about 46 degrees Celsius below zero.

Being an 'outer' planet, that is, orbiting the Sun further than Earth, Mars can be comfortably observed for long periods of time, except when it is not in 'solar conjunction', that is, on the line of sight of the King Star. The best time to observe it is when it is in 'opposition', which is when the Earth passes between the Sun and Mars. In that configuration, the red planet is completely illuminated from Earth and is visible for much of the night.

Conjunction and opposition

Our readers will probably remember the last opposition of Mars, in July 2018, when the red planet shone very generously during the long summer nights. Since then, in its trajectory around the Sun, Mars was placed in apparent positions closer and closer to the line of sight to the star king until it reached its solar conjunction on September 2, when it was completely unobservable.

Now Mars is still on the other side of the Sun, about 380 million kilometers away, but as it has been emerging from the conjunction, it reappears in the sunrises, becoming the only morning star. Its enormous distance makes its brightness very discreet, about 60 times smaller than the one it presented in its last opposition, in July 2018.

Although very low on the horizon and with that discreet brightness, we can see it from the weekend of November 1 to 3 shortly before dawn, at about 6:30. Fortunately, the red planet is already on its way to its next opposition that will reach in a year, specifically on October 13, 2020. Mars will not be as bright as in the last opposition of 2018, but we will see it higher in the celestial vault favoring the observations.

Conjunction of three planets with the Moon

Recall that in these autumnal days Jupiter and Saturn continue to look ostentatiously during the first part of the night, while Venus is also visible very low in the west just at sunset.

On the weekend of November 1 to 3, these three planets will form beautiful scenes with the thin edge of the crescent moon. These stars should be observed at about 6.30 p.m., when the Sun has just set. Venus, Jupiter, Saturn and the Moon will be on the same line of the ecliptic, but Selene will vary her relative position from one day to next, finding each day a little higher, if we observe at the same time.

The four stars will go to bed gently, behind the southwest horizon, one after the other, and at about 10 pm none of them will be visible.

Rafael Bachiller is an astronomer and director of the National Astronomical Observatory (IGN).

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