Mon Jun 22, 2026 ANCIENT SUN TEMPLES
Stonehenge, built over forty centuries ago, is one of over a thousand circles of standing stones that can be found throughout the British Isles and Europe. On the first day of summer, the sun rises over an outlying heelstone, as viewed through a central arch of stones. In ancient Egypt, temples were built so that at the summer solstice, the sun’s rays shone through tall columns to sanctuaries within. At the Bighorn medicine wheel in Wyoming, piles of carefully placed stones point toward the summer sunrise. For hundreds of years in New Mexico, a slender ray of sunlight – the sun dagger of the Anasazi – sliced through a petroglyph spiral on the first day of summer. And there is the Sun Temple, built by the Incas at Machu Pichu – but of course Peru is south of the equator, and now it is their winter solstice sun that is framed in this ancient observatory’s window.
Tues June 23, 2026 PLUTO AND ITS MOONS
On June 21st, 1978, Pluto's moon Charon was discovered by the American astronomer James Christy. In mythology, Pluto was god of the underworld. Charon was his ferryman, who transported souls across the river Styx to the other side. Styx is another, more recently discovered moon, along with three more – Hydra, Nix and Kerberos. Charon is the biggest one, it’s about half the size of Pluto. So when it orbits this distant world, Charon's mass has a substantial effect on Pluto, pulling it first one way, and then the other. In the year 2015, a space probe flew past Pluto and Charon, and sent back incredible pictures and information – ice mountains two miles high, vast nitrogen ice plains, and mysterious dark patches on Pluto’s farside. If you visit the website NASA dot gov, and enter the word “Pluto” in the search box, you can see these pictures for yourself.
Wed Jun 24, 2026 ERATOSTHENES MEASURES THE EARTH
In late June, in the year 240 BC, the astronomer Eratosthenes calculated the size of the earth. He did it by using the changing angle of sunlight at different latitudes in Egypt. Eratosthenes made two assumptions: 1. the earth is round; 2. the sun is far away, so its rays fall parallel across the whole earth. At Alexandria, the sun is about 83 degrees, or 7.2 degrees off the zenith) at noon on the first day of summer. 500 miles to the south was a town called Syene, where on the same day, the sun’s image at noon could be seen reflecting off the water at the bottom of a deep well. There the sun was at 90 degrees altitude, directly overhead. The Alexandria - Syene distance must therefore be 7.2/360th, or a fiftieth of the earth’s circumference. Now Syene was 500 miles away, so he multiplied 500 by 50, and got 25,000 miles for an answer. He was off by a hundred miles – “pretty good work for 2,265 years ago!”*
*Carl Sagan quote from “Cosmos”
Thu Jun 25, 2026 OPTICKS BY NEWTON
Today’s Skywatch was written by Hallstrom Planetarium theatre assistant Vela De la Mare. When looking up at the stars in the sky, the night is awash with color. There are red supergiants like Antares in the constellation Scorpius, blue giants like the brilliant Vega in Lyra, and many shades in between. But how do we define that spectrum? When we think of a rainbow, why is red on one end, and blue on the other? Isaac Newton himself must have asked the same questions, and back in 1704, he published a book called Opticks. It covers many topics such as refraction – that classic experiment where white light is split through a prism, and the different bands of color are dispersed based on their speeds and wavelengths – blue has the shortest waves, and travels the fastest, while red’s long waves take more time to travel through the prism. Opticks goes into such useful detail that it’s still being published to this day.
Fri Jun 26, 2026 HEBER CURTIS
The American astronomer Heber Curtis was born on June 27th, 1872. He found strong evidence that the Milky Way was but one of many countless galaxies, what he called “island universes” in outer space. In 1920 he revealed that he had found novas, stars that periodically brighten and dim, nestled among many spiral nebulas. Because they were very dim, he calculated that these novas were millions of light years away – too distant to be within the borders of our own galaxy. He was right! Curtis studied and photographed many nebulas and galaxies, discovered a jet of matter shooting out from the giant elliptical galaxy M87, (we now know it is powered by an enormous black hole at the galaxy’s core), and carefully observed nearly a dozen solar eclipses in his career. A deeply spiritual man, he declared, “The more I know of Astronomy, the more I believe in God.”
