Following one of the wanderers

Thursday, Sep 11, 2025 11:30 PM Updated Friday, Sep. 12, 2025 7:06 PM

This Jan. 2, 2010 image made available by NASA shows the planet Saturn, as seen from the Cassini spacecraft. (NASA/JPL-Caltech/Space Science Institute via AP)

Greetings, stargazers.

Saturday is named for the prominent figure in Roman mythology. In addition to stargazing, this month should be great for Saturn-gazing.

To ancient astronomers, Saturn was one of the five “wanderers” in the heavens and is brighter than all but a few very bright stars. Because of its distance from the sun, it moves more slowly against the background stars than the other planets visible to the naked eye.

Ever since Galileo looked at Saturn in 1610 it has been one of the most interesting objects to see through a telescope. Galileo saw prominent lobes around the disk of Saturn but was unable to resolve anything that looked like rings. With an improved telescope Christiaan Huygens identified the ring structure in 1655. He also was the first to report seeing Saturn’s moon Titan.

As telescopes continued to improve, more details were resolved. In 1675 Giovani Casini discovered the other four moons that can be seen with most amateur telescopes. He also discovered the dark gap in the rings now known as the Casini gap. Modern six-inch diameter telescopes can easily see all these features.

Saturn’s rotational axis is tilted by 27° compared to the plane of the solar system. As it orbits the sun, the perspective from Earth shows us either more or less tilt to the rings. Earlier this year the plane of the rings was aligned with our view from Earth, so we were viewing the rings edge-on, which made them all but invisible.

Before the Voyager Spacecraft ventured to the outer solar system, Saturn was the only planet known to have rings. Now we know that the other outer planets have rings, but just much smaller and harder to see than the ones around Saturn.

There is evidence that ring structures are short-lived phenomena compared to the four billion year age of the planets. For the short-term ring hypothesis, a moon called Chrysalis disintegrated to become the ring structure. A moon would disintegrate if it got too close to its planet. At this close approach to the planet, called the Roche limit, the tidal forces stretching the moon are greater than the moon’s own internal gravitational forces.

This month

Saturn is at opposition on Sept. 21. That means it will be at its closest approach to Earth and transit the meridian at local midnight on that day. Because of Daylight Saving Time that will be at 1:04 a.m. on Sept. 21. Saturn is about nine times as far from the sun as Earth, so the distance between the Earth and Saturn doesn’t change that much during the year. That means any time Saturn is above the horizon is about as good a time as any other time to view it.

There is also a partial solar eclipse on the same day if anyone wants to venture to Antarctica or New Zealand to see it. If you do, let us know how it goes.

The autumnal equinox is on the Sept. 22, which is the date the sun will be above and below the horizon for 12 hours. However, because the sky is still light for a while after the sun has set, there are only nine hours of true astronomical darkness on the equinox.

Neptune is also at opposition this month on the Sept. 23. Both planets are with a couple of degrees of each other. Unlike Saturn, Neptune is not visible to the naked eye. It appears as a tiny blue dot in even the largest telescopes. Even the amazing view of Neptune from the James Webb telescope that shows its ring structure is fewer than 100 pixels across.