Light Pollution

The widespread use of outdoor artificial light at night (ALAN) results in wasted light directed up into the night sky. Some of that light scatters back down to the ground, diminishing the visibility of astronomical objects. This affects almost every optical and infrared observatory in the world at some level.

An image of a horizon at night with many light sources visible.
A large dish-shaped radio telescope antenna is seen against a blue daytime sky. The sun is casting shadows on its surface. Vegetation appears in the foreground.

Radio Frequency Interference

Observations at a wide range of wavelengths is crucial to understanding our universe. Radio telescopes “see” electromagnetic radiation with frequencies similar to those used for communications on Earth and in space. Human-caused radio interference can severely impact radio astronomical observations.

Space Debris

Space (or orbital) debris is any inactive object in Earth orbit. Today there are over 20,000 objects larger than 10 centimeters tracked, and the number is increasing. Pieces of debris can reflect sunlight to the night side of Earth, interfering with the observations of telescopes. And debris itself may threaten space astronomy missions in orbit around the Earth.

An image of the Earth appears on a black background. The Earth is swarmed by satellites and space debris that form a glowing, granular cloud around it.
Arrays of satellites are seen in the night sky above a foreground with radio antennas built close to the ground.

Satellite Constellations

Satellite constellations, or “SatCons”, are large groups of satellites orbiting the Earth operated for a common purpose, such as telecommunications, by a single user. They may number from the hundreds to the tens of thousands each. Similar to space debris, they can leave bright trails in optical and infrared images of the night sky. They can also cause harmful interference to radio telescopes.