Greetings stargazers.
The night sky is changing. I am not talking about stars disappearing because of light pollution, even thought that is certainly an issue, but I am thinking of all the ways the night sky has changed since humans have been paying attention. These changes can be observed not only century to century, but also from year to year, one night to the next, or even on a shorter time scale.
For thousands of years stargazers enjoyed and strongly believed in the immutability of the heavens. The “fixed” stars were part of the perfection of things unobtainable to us mere Earth dwellers. There were very few things that could be seen moving in the sky – the sun, moon and five planets, and those were often associated with deities. (They correctly, but without evidence, believed that meteors were atmospheric phenomena. The science of meteorology has to do with weather.) Over the centuries, with greater and more detailed observations, our perspective of the universe began to change.
One of the most obvious changes has been the precession of the Earth’s rotational axis. We think of the star Polaris as the pole star, but records show that when the Great Pyramids in Egypt were being built, the pole star was Thuban, in the constellation Draco. This precession is also the reason the astrological zodiac signs don’t align with the sun’s location in the sky like they used to.
Over the course of years stars can also be observed to change their relative positions. Most of this movement is very small, but with accurate photographic records the movement is observable. Binary stars can be seen to orbit each other. One of my favorite timelapse sequences is the motion of stars orbiting the central black hole of the Milky Way.
Variable stars can be seen to change their brightness over a few days or weeks. A very few, such as Algol, an eclipsing binary in the constellation Perseus, can be observed with the naked eye getting brighter and dimmer over the course of several days. The brightness variations can be from within the star itself, or from some external event, as in the case of Algol. The change in observed brightness of a star is the most common way to detect extra-solar planets, as the planet passes in front of the star and blocks some of the light.
On the shortest of time scales, stars can even be seen to explode as a supernova. In distant galaxies new supernovae are found almost daily. The Crab nebula, the remnant of the supernova that exploded in 1054, can be seen expanding in timelapse movies. Colliding black holes have been observed with the LIGO Gravitation Wave detectors. This can be heard as a “chirp.”
The new Vera C. Rubin Observatory has a telescope with an exceptionally large field of view. The main purpose of this new instrument is to make a time lapse of the entire (southern hemisphere) sky over the next decade to see how the universe is changing. I am sure the results will be amazing.
Useful links
This month:
An important date for stargazing this month is Oct. 21, but the several days before and after will be good, too. That is the date of the new moon this month, so it should be extra dark. That date is also the peak of the Orionid Meteor show. The Orionids appear to originate from the constellation Orion but can be seen in all parts of the sky. Orion rises around 11:00 PM. This is typically an average meteor shower, but coinciding with the new moon will help them be more visible. Meteors from this shower are due to the Earth passing through the trail of dust left by Haley’s Comet.
Saturn is still the brightest planet in the evening sky, and its ring is still nearly edge-on. Jupiter, which has been in the morning sky recently, is rising earlier each day and by the end of the month will be above the horizon before midnight.
Predictions of a comet’s brightness are notoriously unreliable, but there are two that might be visible to the naked eye this month. Comet C/2025 A6 (Lemmon) makes its closest approach to Earth on Oct. 21, and Comet C/2025 R2 (SWAN) makes its closest approach Oct. 19.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
