For the first time in history, the administration of the Iguaçu National Park authorized an overnight expedition to the Iguaçu Falls. The result is spectacular photos that show the heaven starry on one of the main postcards of the country, and considered one of the 7 natural wonders of the world.

Milky Way over Iguaçu Falls - Photo: Victor Lima /Trilhadeestrelas.com
Milky Way over Iguaçu Falls - Photo: Victor Lima / Trilhadeestrelas.com

One of the things that draws the most attention when we see this type of photograph is the amount of stars in the sky. We can't see them every night when we look up at the sky from our backyard. But why?


First, there is a question technology. Such photos are taken in long exposure, with the camera sensor exposed to low light for several seconds, accumulating each photon of light to form the image at the end of the exposure. But the main reason most of us don't see such a starry sky is because of light pollution.

Light pollution

Light pollution is the type of pollution caused by artificial lights, typical of large urban centers. It interferes with different ecosystems and causes negative effects on human and animal health. In addition, it obscures the night sky, reducing the visibility of the stars and making it difficult to practice astronomical observation in large centers.

Light pollution in Mexico City. Credits: Fernando Tomás
Light pollution in Mexico City. Credits: Fernando Tomás

Since man dominated fire at least 1 million years ago, mankind has also dominated the night. In primitive times, we spent the first hours of the night in long conversations around a campfire, in which our ancestors recounted their daily adventures, passed on their knowledge and legends. When the last embers were extinguished, a starry sky was projected above all.

This is how our vision works: when the luminosity is high, our pupils contract, reducing the amount of light that reaches the retinas, at the bottom of our eyes. As the light decreases, the pupils dilate, allowing the retinas to receive more light. So we can see well, even in low light environments. When the last embers of the fire went out, the only light that still existed in the night of that world without civilization, was the light of the stars. Their pupils, in maximum dilation, allowed them to see an enormous amount of faint stars, which previously did not seem to exist

This starry sky inspired legends, guided us in our migrations around the globe and gave rise to the oldest of Sciences, Astronomy. However, at the present time, only a small portion of the world's population still has the privilege of seeing such a sky.

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Light pollution separates us from the stars

In 1994, a magnitude 6.7 earthquake rocked Los Angeles and caused a blackout across the city and the surrounding area. It was four-thirty in the morning, but people, for security reasons, left their homes and took to the streets to wait for the tremors to cease.

Without public lighting, and without car lights due to the late hour, many found themselves for the first time in front of a truly starry sky. The emergency service, which normally receives many calls during an earthquake, began to receive reports from residents who were seeing “strange silver smoke crossing the sky over the city”. It was the Milky Way, which they had never seen before.

Light pollution from Los Angeles in 1908 (left) and 2017 (right). Credits: UCLA
Light pollution from Los Angeles in 1908 (left) and 2017 (right). Credits: UCLA

Most of the readers of this text probably never had that opportunity, either. Two thirds of the Brazilian population lives in places where light pollution prevents the visualization of this whitish cloud in the sky, formed by gases billions of stars in the arms of our galaxy. And, as light pollution keeps us farther away from the stars, initiatives emerge that try to rescue the darkness of the night sky.

International Dark Sky Week

Every year, International Dark Sky Association (IDA) promotes International Dark Sky Week (IDSW) to raise awareness of the various negative effects of light pollution. This week always happens when the sky is darker (close to the New Moon) and the stars are more visible. This annual event was created in 2003 by then high school student, Jennifer Barlow. Since then, the International Dark Sky Week has grown to become a worldwide event and a key component of Global Astronomy Month. During the week, dark sky advocates around the world connect with the common goal of protecting the night.

In 2021, the International Dark Sky Week takes place between April 05th and 12th, and IDA invites everyone to discover the beauty and importance of a dark sky. This is the best week to discuss ways to fight light pollution and also a great opportunity, for those who can, to observe a dark and starry sky.

Milky Way and starry sky seen from the rural area of ​​Maturéia, PB. Credits: Marcelo Zurita
Milky Way and starry sky seen from the rural area of ​​Maturéia, PB. Credits: Marcelo Zurita

Unfortunately, due to the Covid-19 pandemic, we must avoid unnecessary travel and displacement. But for those who are in places farther from the big urban centers, we recommend taking advantage of a cloudless night, turning off the lights, and contemplating all the beauty of the sky, just as our ancestors did around the last embers of the fires.

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