It doesn’t take an experienced astronomer to realise that the night sky gradually changes throughout the year. Stars appear to rise four minutes earlier every day, a phenomenon resulting from the Earth’s rotation around the sun. Different parts of the cosmos become visible to us here on Earth as the night side of the planet faces a slightly different direction every day. Gaze out at the night sky on two nights which are exactly six months apart, and you’re looking at a night sky filled with entirely different stars and cosmic wonders.

As the colder months for the northern hemisphere approach, looking up towards the southern skies from Malta presents avid astronomers with a familiar sight, even those living in highly light polluted areas. Three bluish-white stars form a line, separated by an apparent equal distance; two stars lie on either side, flanking the trio.

On one side, a notably reddish-orange star burns bright; on the other, a blue star shines even more brilliantly. If you’ve seen this arrangement of stars in the winter sky, you have gazed upon the Orion constellation, one of the more famous regions of the night sky.

The bright reddish-orange star is one of the more well-known stars visible from Earth. Betelgeuse is a supergiant star with a highly variable brightness, increasing or decreasing in luminosity by a factor of 10 between periods of highest or lowest brightness. It is also an imminent supernova candidate, with its explosion expected to occur anytime in the next million years. If Betelgeuse does explode, it will likely increase in brightness to outshine the full moon, making it easily visible from Earth even in daytime for a few months before rapidly dimming.

The trio of stars arranged in a line are referred to as Orion’s belt. Extending from beneath Orion’s belt, towards the side of the bright blue star named Rigel, is another trio of fainter ‘stars’ named Orion’s sword. The middle one of the three is no star at all, but is instead the nearest active star forming region to Earth.

At a distance of around 1,300 light years, the Orion nebula is easi­ly visible through a telescope as a faintly glowing hue of gas and dust. Long exposure images show intricate detail in the nebula’s outer arms of gas and dust, from which young stars are currently being born. From a dark sky location, a faint purple haze can be seen with the naked eye in the region of the nebula after dark adaptation.

Josef Borg is currently a PhD student at the University of Malta’s Institute of Space Sciences and Astronomy and vice-president of the Astronomical Society of Malta.

Sound bites

• Gravity@Malta 2018 conference hosted in Malta. Malta will host an international conference on gravitational waves, black holes and fundamental physics. This will bring together theories, people working on computer simulations, as well as a number of members from gravitational wave observatories. The conference will centre around the status of current observatories and how future planned observatories will change the landscape of the field. It will also focus on how these kinds of observations can help sieve through the plethora of theories currently being proposed to explain how these exotic events take place.

• Fireball over Michigan. On Tuesday evening, January 16, people in Ohio, Michigan and Ontario, Canada, were treated to the awe-inspiring view of a meteor streaking across the night sky. At 8.09pm local time in south-eastern Michigan, hundreds of people reported hearing a loud boom from the meteor and feeling the ground shake, according to the US Geological Survey (USGS).

www.livescience.com/61452-did-meteor-cause-michigan-earthquake.html

• To find out some more interesting science news, listen in on Radio Mocha every Monday and Friday at 1pm on Radju Malta 2.

Did you know?

• Some stars currently visible in the night sky are no longer actually there. Light tra­vels at the fastest speed possible in the known universe, at around 300,000km every second. However, stars are at least trillions of kilometres apart, which means that light from stars actually takes years to traverse the cosmos and reach us here on Earth. Even the sun is eight light minutes away! Some stars, hundreds of light years away, might have already died hundreds of years ago but light is still reaching us from the time they were still alive. Every time we look up to see the stars, we’re looking at different points in their past, depending on their distance away from us. As an example, Betelgeuse is around 600 light years from Earth. If we see Betelgeuse explode today, it would mean that the star actually exploded in the 15th century, as the light that left the star is only just reaching us now.

• The larger the star, the shorter its life expectancy. Although it might seem somewhat counter-intuitive, larger stars tend to live for a few million years while the smallest dwarf stars have an estimated lifetime of trillions of years. Larger stars, although having a much larger fuel supply, tend to burn their fuel at a much faster rate due to the high temperatures they reach at their core as a result of the high gravitational pressure they exert due to their massive size. Smaller stars not only burn their fuel more slowly but they can also use their entire supply of fuel, as opposed to larger stars, which will only use the fuel present in their core.

• The sun is classified as a low-mass star. Although the sun is massive when compared to our planet, it is actually categorised as one of the smallest kinds of stars. Although it is not a dwarf star, the sun’s lifetime still exceeds that of massive stars by far – at five billion years old, the sun is only halfway through its entire estimated lifetime. Apart from having a low mass, the sun’s diameter is also small when compared to that of some other massive stars. Betelgeuse’s diameter, for example, would extend to beyond the asteroid belt if it were to be placed at the centre of the solar system, engulfing Mercury, Venus, Earth, Mars and possibly even Jupiter.

For more trivia, visit www.um.edu.mt/think.

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