September is usually a month of returning to the routine and remembering what was enjoyed during the summer, however we can still take advantage of the good weather at the end of summer (and with the cool weather that timidly shows itself, with the arrival of autumn) to go out to the countryside to enjoy a day away from the hustle and bustle of the city, with night sky observation included. With the arrival of September we have left behind the meteor shower of the Perseids and the opposition of bodies such as Saturn and Vesta , to enjoy other planets in opposition such as Jupiter and Neptune , as well as an occultation of Uranus by the Moon . In addition, we can still enjoy some elements of summer while the most autumnal and winter stars are gradually showing themselves.
As far as constellations are concerned, September is a month of transition between the more properly summer and winter landscape , having at the beginning of the night a sky dominated by the summer triangle, with the constellations of the Lyre, the Eagle and the Swan well visible. These constellations, however, hide behind the horizon towards the end of the night, while other constellations such as Orion and Canis Major appear on the opposite side of the sky . The constellations of the zodiac, those that are located in the ecliptic, the line that the Sun traces in the sky during the year, more typical of the summer sky, such as Libra, Scorpio, Sagittarius or Capricorn give way to others such as Aries, Taurus, Gemini or Cancer .
As far as the Moon is concerned, we will start the month with a crescent moon that will reach its maximum brightness on September 10 and return to the darkness of the new moon on September 25 . The Moon’s brightness, though of course pales in comparison to the Sun (it makes sense, since the Moon shines only because it reflects the light of the star, without emitting its own light), can be considerable. This is why observing the night sky on full moon days is usually discouraged and is usually recommended at the opposite time of the lunar cycle, when the moon is in new phase. This lunar brightness becomes such that it can be enough to walk through the countryside just under its light and that is certainly enough to cast shadows as if it were a lighthouse .
The Moon will also be the protagonist of one of the astronomical events of the month, as it will cause the occultation of Uranus behind itself on September 14 , between 11:10 p.m. and 12:03 a.m. This occultation will take place low above the horizon, so its beginning will be difficult to see, making the reappearance of the giant planet behind our satellite more accessible.
Another astronomical event that will not be visible in the night sky but will undoubtedly affect our daily lives is the equinox that will take place on September 22 . During this equinox the northern hemisphere will enter fall while the southern hemisphere will begin spring . This equinox is the moment when the Sun goes from being above the celestial equator to being below it, as seen from the northern hemisphere. The celestial equator on the other hand is nothing more than the projection of the circle described by the terrestrial equator on the celestial vault. This will have the consequence that the Sun will reach an increasingly lower height above the horizon of the northern hemisphere until it reaches its minimum during the solstice of December 21, when winter will begin in Spain and the rest of our hemisphere. The opposite will occur in the south , with the Sun rising higher and higher, culminating in the summer solstice near the end of the year.
In addition to all this, September will be an exceptional month for observing (with telescopes or binoculars) the gas giants . On the one hand , Saturn has just passed through its opposition , the point at which the Earth “overtakes” the planet in its orbit, placing itself at a minimum distance from it, so that even with a modest telescope we will be able to distinguish its rings . We will need somewhat more sophisticated equipment to be able to identify some of its moons, the largest and most visible being Titan, but it will not be impossible, given good atmospheric conditions. On the other hand, in September two more planetary oppositions will take place: Jupiter on September 16 and Neptune on September 25 . The first will be especially easy to locate, being the brightest object in the night sky , while to locate the second we will need a mid-range telescope and a good knowledge of the sky. Jupiter will of course be accompanied by its four main moons , those first observed by Galileo Galilei more than 4 centuries ago, which will be visible even with powerful binoculars .
