Clouds over Atacama: tips for avoiding cancellations
Many of the best nights I have had outside my work as an astrotourism guide have been nights when clouds and the moon take over the sky. The clouds give depth to the stars behind them, and the moon lights them from behind.
They are nights worth going out for a walk, wandering the town's quieter streets in this half-darkness, nights for seeing the world in a light that no longer exists in cities.
However, if you want to enjoy the sky, learn the constellations and observe through telescopes, clouds are an obstacle, and there is one particular period of the year when clouds take over the night: the season of summer rains, better known as the Altiplanic winter.
In this article you will find:
The Altiplanic winter: the cloud season in San Pedro de Atacama
The Altiplanic winter is a climate phenomenon that occurs between late January and early March. During this period, the summer rains bring fertility to the desert, transforming the landscape with their own particular light, colour and scents.
Although this phenomenon is vital to the region, it also brings cloudy skies that affect conditions for astronomical observation. Many tourist attractions located above 3,500 metres above sea level also tend to close because of snowfall.
During this period, the clouds generated by the summer rains often cover the sky, creating unfavourable conditions for astronomical observation. Stars, planets and other celestial objects are obscured, and the night sky loses its usual clarity.
The impact of clouds on astronomical visibility
Mid- and low-level clouds have a major impact on astronomical observation. They usually block the sky completely, preventing any kind of observation.
High clouds, although they don't always block visibility completely, affect the quality of observation. They can blur stars and planets, reducing the contrast and clarity of the sky. And if high clouds combine with moonlight, observing conditions deteriorate significantly, making fainter celestial objects difficult to see.
For these reasons, when there is cloud cover, the best option is to cancel the stargazing tour.
Occasional cloud: beyond the Altiplanic winter
San Pedro de Atacama offers more than three hundred cloudless nights a year. However, although the Altiplanic winter is the main cloudy period, skies can occasionally be overcast at other times of the year. These clouds can appear in any season, and although they are not as frequent as during the summer rains, it is common for each observation cycle to involve cancelling one or two outings because of the weather.
How is the decision to cancel a stargazing tour made?
When it comes to deciding whether a stargazing tour should be cancelled, our approach is meticulous and data-driven, but always with the people visiting us that night in mind.
On days with unfavourable conditions, we do three main things:
We monitor the sky hour by hour to follow how atmospheric and cloud conditions develop.
We constantly monitor at least three sources of weather information: Ventusky, Windguru and Meteoblue Astronomy Seeing.
We compare the day's conditions with previous nights to try to predict whether the trend over a given run of nights is persistent cloud or cloud that clears.
Through this process we try to make the best decision, so that any cancellation is made with as much accuracy and consideration as possible.
What happens when a stargazing tour is cancelled?
If the weather does not allow the tour to go ahead, there are two options:
a 100% refund
rescheduling for another night.
Because of high demand and advance bookings, there may not always be space on the first session the following night. However, whenever possible, we open a second time slot to extend availability and make room for those who want to reschedule.
Tips for minimising the impact of cancellations
Book your stargazing tour for the first days of your stay. That way, if the weather is unfavourable, there will be more opportunities to reschedule.
Choose the best dates. Although occasional cloud can appear at any time of year, the Altiplanic winter is the period most prone to cloudy skies. If your main goal is to observe the sky, avoid planning your visit during this period.
A personal recommendation
Not all is lost when an outing is cancelled. I know you came to observe the sky, but if your stargazing tour is cancelled, you can enjoy the sky in another way. Something I wholeheartedly recommend is going for a walk through the streets around San Pedro. The town is a safe place, and believe me, you won't regret walking at night through streets that have no street lighting.
Less than five minutes from Calle Caracoles, you will discover a San Pedro hidden behind the lights and noise of the centre. If you walk south along Calle Domingo Atienza, or south along Calle Antonio León, you will find dirt roads lined with trees and planted fields that, under a half-starry, cloudy or moonlit sky, will give you an experience you didn't expect to find. That is what I would do if my own stargazing tour were cancelled, based on what I have lived through over these long years in San Pedro.
The sky over San Pedro de Atacama is a spectacle worth experiencing, but nature is unpredictable. Planning and flexibility are key to making the most of an astronomical experience in this corner of the world. Understanding that cancellations are sometimes necessary because of the weather will help visitors value clear nights, and the vastness of the universe unfolding before their eyes, all the more.
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