Skywatch for the week of June 23,2026
By Jon U. Bell
June 20, 2025 at 9:13 PM EDT
Skywatch Monday 6-23-2025.mp3
Mon June 23, 2025 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.
Skywatch Tuesday 6-24-2025.mp3
Tue June 24, 2025 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 2,264 years ago!”*
*Carl Sagan quote from “Cosmos”
Skywatch Wednesday 6-25-2025.mp3
Wed June 25, 2025 NEW MOON; SYZYGY
The moon is new today, which means it’s in between the earth and the sun. When three celestial objects line up, we refer to this alignment as a syzygy – s y z y g y. In the case of the earth, moon and the sun, syzygies happen every two weeks, at new moon or at full moon. A new moon syzygy is called a conjunction because the sun and moon are together in the same part of the sky. A full moon syzygy is called an opposition because the moon is on the opposite side of the sky from the sun. Most earth-moon-sun syzygies are rough alignments because the moon’s orbit of our planet is offset by 5 degrees from the earth’s orbit of the sun. but about every six months, during what’s called an eclipse season, the orbital planes of the earth and the moon intersect with the syzygy points (the intersections are called nodes,) and then you have a perfect syzygy which results in an eclipse.
Skywatch Thursday 6-26-2025.mp3
Thu June 26, 2025 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.”
Skywatch Friday 6-27-2025.mp3
Fri June 27, 2025 NAME THAT CONSTELLATION - JUNE
Can you identify the thirty-first largest constellation? It is bordered on the north by the constellation Lynx the Bobcat, and on the south by Hydra, on the west by the Gemini, and on the east by Leo the Lion. There are no bright stars here, and it is one of the darkest regions in the night sky. But there is a beautiful open star cluster within its borders, known as the Praesepe or Beehive cluster, and some of its stars have been found to have planets orbiting them. In mythology it was a crustacean that was sent by the goddess Hera to attack the hero Hercules. It was accidentally crushed by Hercules during the fight, but Hera restored it to life in the heavens as a constellation. This evening the waxing crescent moon appears near the Praesepe cluster. Can you name this star figure, the third constellation of the Zodiac? The answer is Cancer the Crab, high in the southwest after sunset.
Mon June 23, 2025 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.
Skywatch Tuesday 6-24-2025.mp3
Tue June 24, 2025 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 2,264 years ago!”*
*Carl Sagan quote from “Cosmos”
Skywatch Wednesday 6-25-2025.mp3
Wed June 25, 2025 NEW MOON; SYZYGY
The moon is new today, which means it’s in between the earth and the sun. When three celestial objects line up, we refer to this alignment as a syzygy – s y z y g y. In the case of the earth, moon and the sun, syzygies happen every two weeks, at new moon or at full moon. A new moon syzygy is called a conjunction because the sun and moon are together in the same part of the sky. A full moon syzygy is called an opposition because the moon is on the opposite side of the sky from the sun. Most earth-moon-sun syzygies are rough alignments because the moon’s orbit of our planet is offset by 5 degrees from the earth’s orbit of the sun. but about every six months, during what’s called an eclipse season, the orbital planes of the earth and the moon intersect with the syzygy points (the intersections are called nodes,) and then you have a perfect syzygy which results in an eclipse.
Skywatch Thursday 6-26-2025.mp3
Thu June 26, 2025 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.”
Skywatch Friday 6-27-2025.mp3
Fri June 27, 2025 NAME THAT CONSTELLATION - JUNE
Can you identify the thirty-first largest constellation? It is bordered on the north by the constellation Lynx the Bobcat, and on the south by Hydra, on the west by the Gemini, and on the east by Leo the Lion. There are no bright stars here, and it is one of the darkest regions in the night sky. But there is a beautiful open star cluster within its borders, known as the Praesepe or Beehive cluster, and some of its stars have been found to have planets orbiting them. In mythology it was a crustacean that was sent by the goddess Hera to attack the hero Hercules. It was accidentally crushed by Hercules during the fight, but Hera restored it to life in the heavens as a constellation. This evening the waxing crescent moon appears near the Praesepe cluster. Can you name this star figure, the third constellation of the Zodiac? The answer is Cancer the Crab, high in the southwest after sunset.