The Moon will leave us a very dark sky during this weekend because the novilunio will take place on Monday, July 17. Let's take advantage of the planets, there are five visible to the naked eye and forming beautiful scenes in the sky.

At sunset

The Moon will not be an obstacle to observe the three rocky planets of the solar system, brothers of the Earth, which are visible in the evening twilight, because we are on the eve of the next new moon, which will happen on July 17 in the constellation of Gemini.

One hour after sunset, it is advisable to face the northwest in a place with a clear horizon and free of light pollution. Venus, extremely bright, dominates the show, but somewhat higher (about ten degrees apart) we can also observe the discreet reddish glow of Mars. And, between both planets, we can distinguish the star Regulus (from the Latin "little king"), the brightest of the constellation of Leo, which exhibits a beautiful bluish glow.

Jupiter and the Pleiades, July 15-16Stellarium/RB

Venus reaches these days the maximum brightness of the year because it is extremely close to the Earth, only 55 million kilometers (just over a third of the Earth-Sun distance). It is so close that, with binoculars, it is possible to see the phase in which it is, with only a thin arc of the planetary disk illuminated by the Sun. We must take advantage of these days to observe it because as the month progresses, its apparent distance from the Sun will decrease and, at the end of the month, both stars will be practically aligned and will disappear together at sunset. Venus will not be visible until late August when it will reappear at sunrises in the east.

This weekend Mars continues to appear much weaker than Venus, because in recent months, as it travels its orbit around the Sun, it has been moving away from Earth. It is now 2.3 times farther away than the Sun and 6.4 times farther than Venus. This great distance, together with its own characteristics, means that Mars now appears about 400 times less bright than Venus.

To complete this picture, we can also observe the always elusive Mercury, very low above the horizon, but a little higher each day that passes from July 16 to 21. To observe it it is very important to place yourself before a horizon well free of obstacles such as trees or buildings.

At dawn

Early risers who look at the sky before sunrise will be lucky enough to be able to observe two giant planets. To do this, we recommend looking northeast one or two hours before the solar ortho, that is, around 5 or 6 in the morning.

Jupiter will already be low above the horizon, but, despite the colors that light up with dawn, this giant planet is so extremely bright that it can be observed without difficulty. In these mid-month days, Jupiter rises at about 2 a.m. (peninsular time) and from that moment it is possible to see its quiet ascent above the horizon. To its left, as we look at the sky, we can see the Pleiades (or "the seven sisters"), a beautiful star cluster that has been the subject of legends and stories invented by practically all civilizations and throughout the history of humanity.

We have been able to see the thin edge of the waning Moon in the sunrises of all this past week, on Saturday 15 its position in Taurus is very close to that of the great reddish star Aldebaran. On the unlit lunar disk we can observe the always delicate cinderella light, a glow that comes from the reflection of sunlight on our planet, which intrigued astronomers for centuries. The first to give a scientific explanation of its origin was Galileo.

To the south is Saturn which, these days, rises in the east at sunset and remains visible throughout the night. The giant of the rings gets up about 40 minutes earlier each day and, therefore, if we look at it night after night at the same time, we will see that it is gaining in height with each passing day.

If you are lucky enough to observe Saturn with the help of a small telescope, you can get a beautiful view of its fascinating rings because, now, the inclination of these is small, making the perspective on the planet particularly beautiful. And also with a telescope, it is now possible to observe Neptune whose apparent position in the sky is halfway between Jupiter and Saturn. Finally, such a telescope would also be useful for looking at Uranus, which lies east of Jupiter.

These warm summer nights are not the most conducive to professional astronomy because they are short and, in addition, high temperatures increase atmospheric turbulence. But, for the average citizen, who spend more time on the street enjoying the good weather, these are excellent nights to look up at the sky, especially in the twilights, and thus enjoy these beautiful celestial prints that remind us of our origins and our place in the cosmos.

Rafael Bachiller is director of the National Astronomical Observatory (Instituto Geográfico Nacional) and academician of the Royal Academy of Doctors of Spain.

  • Astronomy

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