A 101 years ago, on November 23, 1924, the universe got larger.

A 101 years ago, on November 23, 1924, the universe got larger. Not in a physical sense, but we came to understand how big it really was. The New York Times reported that astronomer, Edwin Hubble, had made a big discovery. He confirmed that many of the spiral objects known as nebulae were really separate galaxies, “island universes” of stars far outside the Milky Way. It was the first public announcement of one of the greatest scientific findings of the 20th century. The discovery dramatically expanded the known universe. Instead of consisting of the Milky Way alone, the universe contained billions of galaxies, spread across billions of light-years of space.

Hubble studied a class of stars in two spiral nebulae – Andromeda and M33. Called Cepheid variables, the stars pulse in and out. Measuring the length of its pulses and other details reveals the star’s true brightness. From that, astronomers can calculate the star’s distance.

Hubble calculated that Andromeda was about 860,000 light-years away, and M33 a bit farther. Modern calculations show that they are about three times farther than Hubble thought. Still, the concept was proved: the universe extends far beyond our galactic home.

Andromeda, now known as the Andromeda Galaxy (M31) is low in the north at nightfall. See the star chart for location. Under dark skies, it is visible to the eye alone, a whopping 2.5 million light-years away. Binoculars will provide a very pleasing view.
A lone blue-white star shines brightly in the early evening south-eastern sky during November. The star is Canopus, the second brightest star in the whole sky. I have always regarded the first sighting of this brilliant star low in the south-eastern sky as a sure indication that the warmer evenings of summer are on their way.

Canopus is quite different from the Sun. It's a supergiant; many times bigger and heavier than the Sun. It is also more than 10,000 times brighter than the Sun, so is easily visible across more than 300 light-years of space. It is nearing the end of its life, and within the next few million years should explode as a supernova. When that happens, Canopus will briefly outshine everything else in the sky except the Sun.

Low in the north-eastern sky, the Pleiades, or more commonly known as the Seven Sisters, can be seen glowing like a small bright cloud in the constellation of Taurus, the bull. Examine them with your binoculars, and they'll transform into a myriad of jewels against the black of the night. The Pleiades is really a cluster of several hundred stars about 425 light-years from Earth. The stars were born about a hundred million years ago from a single large cloud of gas and dust, which makes them all sisters. That seems appropriate, since the Pleiades are the daughters of Atlas in ancient Greek legend.

Currently visiting Taurus is one of the outer planets of our solar system. The planet Uranus is 20 times farther from the Sun than Earth is. It is very cold in the outer solar system. As a result, its 28 known moons all shiver at hundreds of degrees below zero. Yet several of the planet’s bigger moons might have active volcanoes. Instead of molten rock, they belch out molten ice, a slushy brew from buried oceans of liquid water.

We don’t know for sure if any of the moons have ice volcanoes, but there’s evidence that they do. The surfaces of the moons are fairly young, for example. That suggests that something is renewing them – like material from the interior. And a couple of the moons appear to be pumping material into the space around Uranus.

Recent observations by Webb Space Telescope found additional evidence for an ocean on the moon Ariel. It’s coated with frozen carbon dioxide. Webb found the layer of CO2 is especially thick. And it’s mixed with carbon monoxide. Both compounds should quickly vaporize and drift off into space. Their presence suggests the supply is being renewed, perhaps by volcanoes belching ice from a hidden ocean.

There are now over 6000 confirmed exoplanets (planets around other stars), and half of those are about the same size and mass as Uranus and Neptune, two of the giants of our own solar system. But we don’t know much about these exoplanets, in part because we don’t know much about Uranus and Neptune themselves. They’re billions of kilometres away, and only one mission has visited either planet. There is talk of another space mission to Uranus in the future, so it’ll be a while before we get a close look at this common type of giant planet.

Uranus is an oddball. It lies on its side, probably the result of a collision with another planet when it was young. The sideways orientation also gives Uranus a cycle of seasons unlike that of any other planet.

Right now, Uranus is low in the east in the early evening. You can find it just a few degrees to the right and above the Pleiades. You will need binoculars to locate it. The blue-green of its disc makes it unmistakeable.

Another planet also adorns the evening sky. This one is a lot easier to find. Located high in the northern sky between the constellations of Pisces and Cetus, Saturn is not the spectacular sight we have been used to. Its glorious set of rings are seen edge-on and are practically invisible to us. Because Saturn’s axis of rotation is tilted at about 27o , the orientation of its rings changes as it orbits the Sun. Saturn takes just over 29 years to orbit the Sun and our viewing angle shits. Every 14 years or so, Earth passes directly through the plane of Saturn’s rings. During this time, we see the rings edge-on, making them appear as a thin line, or even vanish, because they’re incredibly thin (less than 50 metres thick). The tilt will get larger over the next year, returning Saturn and its rings to the view we are accustomed to.
Fun fact – the rings are over 200,000 kilometres wide, but if we scaled them down to the distance between Perth and Sydney, they would be the thickness of a piece of paper.

The Moon is Full on November 5, at Last Quarter on November 12, New on November 20 and at First Quarter on November 28.

Happy observing!

Above: Saturn as seen in a telescope on the evening of November 15, showing the rings completely edge on. Graphic generated with Stellarium v25.3 software (www.stellarium.org).