See the world’s largest telescope dwarfed by the Full Hunter’s Moon (photo)

Construction of the world’s largest visible and infrared-light telescope, the Extremely Large Telescope (ELT), is currently underway in Chile’s Atacama Desert. The European Southern Observatory (ESO) recently shared a photo of the telescope’s progress, which is expected to see its first light by 2028. The ELT’s steel skeleton now stands at 80 meters high, and when completed, the whole structure will be able to rotate 360 degrees to observe the night sky.

The ELT will be 120 feet wide, making it the largest telescope in the world for visible and infrared light. It will house five separate mirrors, the largest of which will be made up of 798 individual hexagonal segments. The photo released by the ESO features the moon appearing large behind the telescope dome due to an optical effect known as the moon illusion. This effect causes the moon to appear larger near the horizon than it does higher up in the sky.

The photo was taken on October 28, the same day that a lunar eclipse was visible to millions of people in Europe, Africa, Asia, and parts of Australia. It was captured from about 12 miles away, near the entrance of the Paranal Observatory, which is home to ESO’s Very Large Telescope. The ESO team had to carefully plan the photo opportunity to capture the moon rising in the night sky, with just a sliver still tucked beneath the Cerro Armazones mountain.

Although the moon appears extremely large in the photo, this is merely an optical illusion known as the moon illusion. This illusion is experienced when looking at the moon while it is setting or rising compared to when it is higher up in the sky. However, the moon never actually changes in size; it’s just a shift in our perception of how far away the moon really is and how big we expect it to be at that distance.