What is the best season for stargazing in San Pedro de Atacama?
San Pedro de Atacama is a privileged place for observing the sky. Its dry climate and low light pollution allow for a unique observing experience, which brings thousands of people here to enjoy the sky.
In this article you will find:
Standing under the Atacama sky, considered one of the best skies in the world, it is natural to wonder when the best time to come and see it is. I know because I have often been asked, in the conversations that happen around the fire at the end of an observation.
The answer is very simple: it depends.
Which is the best season?
The best season for observing the sky in San Pedro de Atacama depends on what you want to see. Each season of the year has its own particular group of stars, constellations and other features.
Here is a summary of the highlights of each part of the year, beginning with autumn and ending with summer.
Autumn (March – May):
The autumn sky is marked by the return of the Milky Way to the southern sky. Although the centre of the galaxy won't be visible in the early hours of the night, we can see a beautiful band stretching from east to west.
In this stretch of the Milky Way is the Southern Cross, upright early in the night, and beside it Alpha Centauri, the closest star to the solar system visible to the naked eye.
The brightest star in the sky, Sirius, will be setting early in the night, while Antares, the heart of the scorpion, rises in the east. This is the time of year when the Great Bear can be seen, looking north, just above the horizon.
Among the zodiac constellations, the most visible during observations will be Scorpius, Libra, Virgo, Leo and Cancer. Gemini will be setting as Sagittarius rises.
This is the season when the cold that announces winter begins, so it is very important to come to San Pedro with warm clothing.
Winter (June – August):
Winter is without doubt the best season for anyone hoping to see the Milky Way. This is the period when, early in the night, the centre of our galaxy passes overhead, at the zenith, and offers the best visibility of the year. It will cover much of the sky, and the dark regions of the Milky Way are easy to make out.
At this time the Southern Cross tilts westward and we see it lying horizontal, though always pointing towards the South Celestial Pole, the point above the Earth's south pole. Alpha and Beta Centauri will be above it. The Large Magellanic Cloud will be getting ready to set early in the night.
In this season the sky is dominated by the Milky Way and the constellations of Scorpius and Sagittarius at the zenith. To the north is the winter triangle, formed by the stars Vega, Deneb and Altair, in the constellations of Lyra, Cygnus and Aquila respectively.
In the zodiac we will see Capricorn, Sagittarius, Scorpius and Libra, and as Virgo sets in the west, Aquarius rises in the east.
This is the coldest season. Although the temperature is pleasant during the day, don't be fooled: at night the cold takes over the desert. Dressing very warmly is essential.
Spring (September – November):
In spring, the Milky Way settles over the west early in the night and, a few hours later, sets. It hands the sky over to Orion, with Las Tres Marías, which begin to rise in the east.
The Southern Cross sets as soon as night begins, giving way to the reign of the Magellanic Clouds, the two galaxies visible to the naked eye in the southern hemisphere.
This is a sky of transition. The Milky Way with Scorpius and Sagittarius, and Orion, Sirius and Canopus too, are all near the horizon early in the night. It is the time to see some of the beautiful constellations that draw less attention. To the south are the southern birds — the Bird of Paradise, the Peacock, the Toucan, the Crane and the Phoenix — and the great constellation of the river Eridanus. The north is dominated by Pegasus and Andromeda.
Aries, Pisces, Aquarius and Capricorn will also be visible, while Taurus rises in the east and Sagittarius sets in the west. The hard cold is over by now, but the September winds sometimes bring surprising drops in temperature. It is worth being prepared.
Summer (December – February):
In summer the Milky Way returns, not so much as the white band visible in winter, but as a region of bright stars that dominates the sky.
Orion's Belt, which in this part of the world we call Las Tres Marías, will be accompanied by the brightest stars in the sky, Sirius and Canopus. The Southern Cross will rise again in the south-east, returning after its period out of sight and showing us the south once more, while the Magellanic Clouds begin their descent towards the south-west.
The zodiac constellations will be tilted towards the north. Cancer, Gemini, Taurus and Aries will be the most visible. As Pisces sets, Leo rises.
The warm weather has finally arrived. A jacket is usually enough for enjoying the sky.
Weather conditions in San Pedro de Atacama
The climate in San Pedro de Atacama is dry and stable for much of the year, which favours astronomical observation. However, each season has different characteristics that can shape your experience.
Summer (December – February): The nights are warm, but cloud is possible, mainly in February and early March, because of the summer rains. If you come at this time, we recommend booking your tour for the first day of your stay in San Pedro, as this will let you rebook if we have to cancel because of cloud.
Winter (June – August):
Cold but clear nights, ideal for steady, uninterrupted observing, though the temperature can drop below 0°C, especially when cold spells arrive. Good warm clothing is essential.
As a personal example, this is what I wear in winter:For the lower body, a base layer, two pairs of trousers and two pairs of socks.For the upper body, a base layer, a shirt, a fleece, a second fleece and a thick jacket. A hat, a neck warmer and gloves are necessary, and I put them on and take them off to regulate my temperature.
Notable astronomical events
Some seasons also bring special astronomical events:
Meteor showers:
The Geminids in December and the Perseids in August are especially notable.
Phases of the Moon:
Check the lunar calendar and try to favour the new moon and waning phases (above all the seven days before the new moon). At this link you can quickly check the moon's phases and choose the best date for your observing session.
Planet visibility:
Over the course of the year, some planets are easier to observe, which adds to the appeal. You can use various resources to check planet visibility.
Bear in mind that, although apps will show you the positions of all the planets, Uranus, Neptune and Pluto are barely visible through a telescope. And for good visibility, planets need to be near the zenith, or at least far from the horizon.
Tools and resources for exploring the sky
To find out what will be in the sky once you have your tour date, I recommend Stellarium, a free app that lets you see the sky exactly as it will appear on the date and at the time of your tour. Simply enter the date, time and place (select San Pedro de Atacama) and you will get an accurate view of the constellations and celestial objects visible.
Stellarium's features:
Shows the sky in real time from any location.
Lets you search for and locate stars, constellations and planets.
Includes date and time settings for planning future observations.
Download the Stellarium app here.
You can also use Stellarium on your computer here.
Every season in San Pedro de Atacama has something of its own to offer under the night sky. Winter tends to be ideal for clear skies, but each season brings its own character and astronomical events that make the experience special. Depending on what interests you, you can plan your visit around the sky you most want to see.
Remember that you can book with us to share the sky under the night of Atacama.
Warm wishes, Rodrigo
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