Have you looked up on a clear night and been struck by the brilliance of the stars and the depth of the universe? If so, or if you’re just curious about what the night sky has to offer, you’ve come to the right place. September brings astronomical phenomena worth contemplating. You don’t need fancy telescopes or advanced knowledge of astronomy (though we’ve got some tips for those who do). All you have to do is look up at the sky at night to marvel at what’s in store for you.
Before we begin the astronomical phenomena of the month, it may be helpful to make a comment on how to choose a good place to conduct our astronomical observations. The most important thing is to find a place with minimal light pollution. If you don’t have a car or motor vehicle, just try to get as far away from the city you live in as possible. In particular, you should stay away from street lamps and public lighting, as these create most of the pollution that interferes with observing the sky. You should also try to do your observation on a night near the new moon, as the brightness of the moon can prevent you from enjoying the firmament.
If you decide to travel further by car, use one of the light pollution maps you can find online. It is enough to search for “light pollution map” or the English equivalent “light pollution map” to find several pages showing the pollution present worldwide. In general, the less contamination you find, the better. There’s always a clearer sky, whether in the middle of the ocean or in the desert, but the best sky for practicing astronomy is the one we have over our heads. With that said, let’s begin our review of this month’s events.
Since August ended with its second full moon, we start September with a waning moon, which loses its brightness completely on September 15 and then enters the new moon. Although it will be difficult to see, this new moon will pass very close to the Sun in preparation for next month’s eclipse (which can be seen from the US, Mexico, Colombia, Brazil, and Central America). After this day, the moon will increase in brightness until it reaches the full moon at the end of the month, on September 29th, to be precise. This full moon will also pass close to the earth’s shadow in preparation for the lunar eclipse at the end of October. This means that the best dates for astronomical observations will be around September 15th.
Also, if we only have those appointments to go into the field and see the stars, even observing the moon with binoculars or a humble telescope can be a fantastic option. It is particularly interesting to observe the Moon on days near the waxing and waning quarters, as more craters and reliefs can be seen on its surface at this point in the lunar cycle. During the new moon, we cannot observe it due to its darkness and proximity to the sun, and during the full moon, all relief is blurred as the moon is lit “from above” and the shadows disappear from its surface.
With September comes the change of seasons. In the northern hemisphere, we say goodbye to summer and welcome autumn, while in the south, we say goodbye to winter and make way for spring. Although we understand the seasons as a climatic continuum in which heat gradually turns into cold or vice versa, in an astronomical sense, the seasons begin and end at a specific minute of a specific day. For example, this year’s September Equinox occurs on September 23 at 8:50 a.m. Peninsular Spanish Time. This is exactly the time when autumn begins in Spain.
The seasons are caused by the tilt of the Earth’s axis of rotation. In summer, the corresponding hemisphere points towards the sun; in winter, it points in the opposite direction. Specifically, these seasons begin on the day when the hemisphere points exactly at the sun or exactly in the opposite direction. If we were to project the circle defined by the Earth’s equator, we would see how the sun is on that circle in summer, while in winter it is below it. The equinoxes are nothing but the exact moment when the sun crosses this circle and goes from one side to the other. In the northern hemisphere, the sun will transition from above the celestial equator to below it on September 23. As a result, the sun falls less directly on this hemisphere, and it no longer heats it up as much as it does in summer. The opposite will happen in the southern hemisphere.
On September 19, the planet Neptune will be in opposition, that is, it will occupy the position diametrically opposite to that of the Sun in the sky. This is because on that day, the Earth will “overtake” Neptune in its orbit around the Sun. On this day, the planet is at its closest distance from Earth throughout the year, making it the perfect time to observe it. However, since Neptune is the most distant planet in the solar system, this observation will not be easy. It will reach a magnitude of around 7.8, making it invisible to the naked eye. We’ll need a modest telescope and a lot of patience to find it among the myriad of stars that will surround it. Nevertheless, it will be worth it.