This weekend we will witness a beautiful conjunction of Saturn with the waning quarter of the Moon. On Wednesday 14 the conjunction will take place between Jupiter and a thin lunar edge. For a good observation of these conjunctions you have to look at the sky to the east one or two hours before the Sun rises.

Appointment with Saturn

Early risers (and night owls) who look at the sky before sunrise will be lucky enough to be able to observe two giant planets. To do this, it is advisable to look southeast one or two hours before the solar ortho, that is, around 5am or 6am (peninsular time).

Jupiter is low above the horizon, but this giant planet is so extremely bright that it can be observed without difficulty. Of course, it is preferable to choose an observation point with a clear horizon, without trees or buildings, and at altitude if possible.

Further to the right is Saturn, which shines much more discreetly. To be precise, the ring giant has a brightness 16 times less than that of Jupiter. And, if this is 846 million kilometers from Earth, Saturn is 1.7 times farther: 1,431 million kilometers away.

The scene is completed by Fomalhaut, the brightest star in the constellation of the Southern Fish and one of the brightest in the night sky. Located 25 light-years from Earth, it has an intrinsic luminosity 18 times more intense than that of the Sun.

Saturn rises these days around 2 o'clock in the morning, and Jupiter appears two hours later. From those moments, it is possible to see the quiet ascent of the two giant planets until the colors of dawn end up hiding their brightness. If we observe them on successive days, we will see that both get up a few minutes earlier each day and, therefore, if we look at them night after night at the same time, we will see that they gain in height with each passing day.

This weekend, Saturn will not rise alone, but will be accompanied by the Moon that is now in its waning quarter; The full moon took place on the 4th and the novilunio will happen on the 18th. At dawn on Saturday 10, both stars are less than five degrees apart, this is equivalent to the length of the thumb when the arm is extended.

With a small telescope, it is also possible to observe these nights (preferably in those with less lunar illumination) the fascinating rings of Saturn. At this time, their inclination with respect to the line of sight is small, making the perspective on the planet particularly stimulating.

Appointment with Jupiter

On the 14th, the action will have moved to Jupiter, because the Moon, already converted into a very thin illuminated edge, will be very close to the king of the planets. The separation of Jupiter from the illuminated limb of the Moon will then be just over one degree, that is, just over twice the apparent lunar diameter.

Conjunction of Jupiter with the Moon on the 14th day Stellarium/RB

If you are lucky enough to be able to observe the scene through a small telescope, you can get a beautiful view of the giant planet accompanied by its four major satellites: Ganymede, Io, Europa and Callisto. When Galileo discovered these moons in the early seventeenth century, he found that Jupiter behaved with them like a mini-solar system, that not all bodies orbited the Earth, and this provided a major argument in favor of the heliocentric theory that changed the conception of the universe.

With the telescope it is also possible to see surprising details of the lunar relief in the terminator zone (where the transition of the illuminated area with the one in the shadow occurs). And, with or without a telescope, it is always very interesting to observe the dark part of the lunar disk with its delicate ashen glow: it is the reflection of a reflection, it comes from sunlight that is first reflected on the Earth before reaching the Moon.

Short nights

This year the summer solstice will take place on June 21, as we approach that date the nights are shorter and shorter. In our latitudes, we still have about five hours of complete darkness to look at the starry sky in optimal conditions. But at more northern latitudes, the Sun doesn't reach great depth at night and twilight complicates observations for more northern astronomers.

However, in those northern latitudes (above 50 degrees), they are lucky enough to enjoy the wonderful noctilucent clouds that occur in the higher layers of the atmosphere at the end of twilight, when the Sun illuminates from below the horizon. The spectacles of nature, and particularly those that happen in the sky, always fascinate us reminding us that we are part of a wonderful and unfathomable 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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