This weekend we can observe a beautiful conjunction of Saturn with the thin edge of the crescent moon. On Thursday the 18th, Jupiter will be conjunct the lunar fourth.

Visit to Saturn

The Moon, which was in the new moon phase last Thursday the 11th, presents us with a bright crescent edge this weekend. We can look at it shortly after sunset, when the reddish hues of twilight fade to the southwest. At the moment not only is the thin luminous edge visible, if we look carefully we can also see the ashen light dimly illuminating the rest of the lunar disk: this discreet glow comes from the solar radiation that is reflected by the Earth and then reaches our satellite.

If we look at the southwest horizon on Saturday the 13th, an hour after sunset (around 19:15 p.m. peninsular and Balearic time) we can see Selene very low above the horizon and, a little higher, we will see Saturn shining modestly while waiting for the night.

On Sunday the 14th, the conjunction will be much closer, with the Moon and Saturn separated by just four degrees.

The ring giant is now among the stars of Aquarius, but it is distinguished from them by keeping its brightness very stable, while the stars twinkle due to atmospheric turbulence. It is not possible to see Saturn's rings with the naked eye, but an amateur telescope (about 20 or 30x magnification) is enough to give us the fascinating (albeit small) image of this peculiar planet.

The apparent position of Saturn, with each passing day, is getting closer and closer to that of the Sun. We must take advantage of it now to observe it, because we are in the last days in which it is visible, it will disappear from the night sky towards the middle of February swallowed up in sunlight.

Visit to Jupiter

As the days progress, the Moon becomes progressively larger to reach its first quarter phase on the 18th, when exactly half of the lunar disk will be illuminated (the full moon will take place on the 25th in Cancer).

Conjunction of the Moon with Jupiter.Stellarium/RB

And exactly on the 18th, the first quarter will form a beautiful conjunction with Jupiter. The king of the planets is now so bright (magnitude -2.5) that it will make it possible to observe the conjunction from immediately after sunset over the southern horizon, between the constellations of Aries and Pisces. The two stars will be separated by only a couple of degrees (that is, about four times the diameter of the full moon).

What about the other planets?

In fact, during these days, the Moon visits the four gaseous planets: if on the 14th it is close to Saturn and on the 18th to Jupiter, on the 15th it will be close to Neptune and on the 19th near Uranus (see attached illustration). However, these planets are too far away to be observed with the naked eye, and to see these conjunctions requires a telescope.

Conjunctions with the four giant planets. OAN/Stellarium/RB

In this month of January it is also possible to observe Venus shining splendidly at dawn. It will be accompanied by the elusive Mercury from the 5th. However, Mars remains too close to the Sun and will remain unobservable until mid-February when it will appear, also at dawn, accompanying Venus.

Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and member of the Royal Academy of Doctors of Spain.

  • Astronomy