Hanging by a Thread

In this image, one of the Maunakea observatories appears to be hanging by a golden thread. In reality, the thread is a beam of light, and it is not descending from the sky, but is pointing upwards from the telescope itself. It originates from Gemini North, part of the international Gemini Observatory, a Program of NSF NOIRLab. The light beam is a laser guide star , and its purpose is to form an artificial constellation of stars in the atmosphere, 90 kilometers (56 miles) from the Earth’s surface.

Intuitively it seems that the laser beam must be extraordinarily powerful. Remarkably, however, the laser guide star produces about as much energy as a bedside lamp. The reason why light with so little energy can beam so far into the atmosphere is because laser beams are incredibly focused, with all the energy concentrated in a single direction. The laser beam is actually not very visible to human eyes from a distance and is captured here through clever photography techniques. However, it would be very dangerous to look directly into it!