Our ancestors had a deeply profound knowledge of the skies visible from our islands, and this was indeed paramount for their survival. Prior to the introduction of calendars, the different seasons could only be told apart with any precision from our skies. They realised that certain stars were visible in the night sky when the days got longer and warmer, and other stars could be seen when the days got shorter and cooler.
Even though they might not have known why at the time, our ancestors understood that different seasons bring about a change in the constellations they could see above when they gazed up at the starry night sky. Avid stargazers today can also notice this same change in our skies, hardly noticeable on a day-to-day basis, but obvious on a scale of a few weeks or months.
Living on a small rock with one of the highest population densities in the world and the widespread disregard for proper lighting fixtures has made our viewing of the night sky harder than ever before in the entire history of our island’s inhabitants. Yet, some dark sky havens remain, giving us a bittersweet taste of what our ancestors would have effortlessly seen on any cloudless night from anywhere on the island.
The Earth’s rotation around the sun is responsible for the change in skies visible during the year. As the Earth makes its way around the sun, the night-facing side of the planet looks out towards a particular region of space, in the exact opposite direction from where the Earth’s night-facing side would look towards six months later. This means that slightly different viewpoints to the cosmos are available to us every night, with stars appearing to rise and set four minutes earlier every day. While this small change does not seem like much from night to night, it also means that stars that rose at 10pm today will rise at 9pm in 15 days’ time. Eventually, stars that rise and set during daytime will rise and set during the night, and vice-versa, and hence why different stars are seen throughout the year.
The stars in the Orion constellation, for example, have long been synonymous with the colder, winter months. Conversely, the constellations of Cygnus and Scorpius are associated with the warmer, summery months on our island.
It might indeed seem trivial to think about the changing skies we experience throughout the year. Yet those same changes allowed us to gain a deep understanding of the workings of our planet itself, and understanding our planet’s rotation on its own axis and around the sun has given us the notion of time we are all familiar with today.
Josef Borg is a PhD student at the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Did you know?
• The constellations will not remain the same forever. The stars in all the constellations visible from Earth are all found within our own galaxy, the Milky Way. All of these stars have their own orbit around the centre of our galaxy, which means that some of these stars will eventually move slightly faster or slower and in slightly different directions from the other stars in the same constellation. The Earth itself, orbiting around the sun, is hurtling in space in its orbit around the centre of the galaxy. Eventually, the positions of the stars will change, and therefore the shapes of the constellations will also change.
• The constellations visible in particular seasons will also eventually change. The Earth’s rotation on its own axis is not always going to remain tilted at the current approximate tilt of 23 degrees. This is due to a wobble in the Earth’s rotation, called a precession. Eventually, in around 20,000 years, the northern celestial pole itself would have moved from the northern star, Polaris, to Vega.
• Names of many stars in constellations with Greek names are in Arabic. Constellations like Cygnus and Orion contain several stars with names given by Arabic astronomers. Of interest for Maltese readers is that the names of these stars are easily recognisable based on where they are found in their constellation. For example, the constellation Cygnus (the Swan) has the stars Deneb (in Maltese, denb, meaning ‘tail’) where the tail of the swan would be as imagined by Greek astronomers; Sadr (in Maltese, sider, meaning ‘breast’) where the swan’s breast would be, and Gienah (in Maltese, ġwienaħ, meaning ‘wings’) where the swan’s wings would be.
Sound bites
• A base on Mars? It could happen by 2028, Elon Musk says. Humanity could have an outpost on Mars just a decade from now, Elon Musk said. Musk’s company SpaceX is building a huge, reusable rocket-spaceship duo called the BFR to help our species explore and settle on the Earth’s moon, as well as on Mars and other worlds throughout the solar system. The billionaire entrepreneur’s long-term vision involves the establishment of a million-person city on the Red Planet in the next 50 to 100 years. But we could get the founding infrastructure of such a settlement – an outpost Musk calls Mars Base Alpha – up and running much sooner than that, he said.
https://www.space.com/41935-mars-base-alpha-2028-elon-musk.html
• Hayabusa 2 deploys rovers to explore Ryugu. The Japanese Aerospace Exploration Agency’s intrepid Hayabusa 2 mission deployed the first of a series of asteroid landers and rovers on September 21 at 4.06 UT / 12.06am EDT. Built by a team at the University of Aizu, Japan, the Micro-Nano Experimental Robot Vehicle for the Asteroid (MINERVA II) project hitched a ride on the Hayabusa 2 mission as it travelled for three-and-a-half years from Earth to the 0.6-mile-wide (one-kilometre-diameter) asteroid 162173 Ryugu.
https://www.skyandtelescope.com/astronomy-news/touchdown-hayabusa-2-deploys-rovers-explore-ryugu/
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