Looking out at the universe we see stars and galaxies, as well as many other less luminous objects, but what’s interesting to cosmologists is how and why they are moving. On small scales such as in the solar system we see planets orbit about the sun and further out we observe stars to be orbiting about the Milky Way galaxy’s core. Even our nearest neighbourhood of galaxies seems to be affected by and large only by themselves. However, when we look at the movements of galaxies much further away, we see a general trend. Galaxies not in our neighbourhood of the universe appear to be moving away from us in relation to their distance away from us. That is, if a galaxy at some distance is moving away at some speed, then a galaxy twice as far will be moving away from us at double that speed.

This does not mean that we are at the centre of the universe since if every group of galaxies is moving away from every other group, then an observer in any galaxy would see the same effect. This in itself is not a strange thing, given that the universe was created roughly 14 billion years ago in the Big Bang, this is merely the after-effect of that initial explosion.

This was the picture up to 1998 when two groups, the Supernova Cosmology Project and the High-Z Supernova Search Team, discovered a seemingly bizarre effect. They found that the universe appears to be accelerating in this expansion. They did this by looking at very special stars that are approximately the same in brightness wherever they are in the universe. Now, given that the normal matter we see in the universe appears to be gravitationally only attractive, something different must be at play. The observation is attributed to what has come to be called, dark energy.

It is still unclear exactly what this is but there are two general options for what it might be. It is either a very weak energy that is uniformly distributed over the whole universe. If so, this wouldn’t add up to very much for volumes like the Milky Way, but on the scale of the whole universe this would slowly take over as the universe expands.

On the other hand, this anomaly is dependant on our model of gravity. In the present case, we use Einstein’s 1915 general theory of relativity which has so far served us well and given us GPS as well as a much better understanding of the physics at play in the solar system, but this may need some tweaking.

The jury is still out on which solution will explain this phenomenon but our local contribution comes from the Institute of Space Sciences and Astronomy. Part of our work is focused on working on competing theories of gravity where this effect arises naturally without the need of exotic energies.

Sound bites

• The 2016 leap second – Did you know that 2016 was not only a day but also a second longer than 2015? We’re all used to the leap year and the need for it, namely that a year is not really 365 days but 365.25 days. That means that every four years we get a whole extra day that doesn’t exactly fit into our whole number of days calendar. This fact was known even when the Julian calendar, named after Julius Caesar, was implemented in 45 BC. This has since been updated to the Gregorian calendar where the exact placement of the leap year has become better defined to its current frequency. The goal of this calendar was to standardise the length of a year as much as possible with respect to the astronomical objects on the sky. A more accurate measure of the seasons was then ascertained. However, as time passed, timekeeping became much more accurate, with atomic clocks now being the standard way to accurately tell the time. Moreover, the small divergences between this value and the slight variations in the actual length of the years grew. The source of this difference lies in the fact that the earth’s rotation about the sun is affected by slight variations on its path. Currently, it is the responsibility of the International Earth Rotation and Reference Systems Service (IERS) to monitor these variations and when necessary to add a leap second to delay the atomic clock reading. The IERS has found that on average the earth runs 1.5 to two milliseconds late every day. This obviously doesn’t mean much for our daily schedule but over 500 to 750 days it adds up to a full second. Not accounting for it would, over time, result in basic elements of the day not being matched up with our clock measurements such as solar noon.


• Picturing the universe – Pan-STARRS1 Observatory releases largest survey of the visible universe yet: The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) consists of two 1.8m reflector telescopes equipped with the largest digital camera with respect to its field of view. This camera can take in 1.4 billion pixels per image, this translate to two gigabytes of storage per image. An average night could take up to 10 terabytes of data to store. The Pan-STARRS1 Observatory rests on top of the summit of Haleakalā, on Maui, Hawaii. Besides the scenic location, the telescope has to be placed at these sorts of places to avoid the filtering effects of lower altitudes such as humidity in the air and bad weather conditions. Over the past four years, the team behind the operation has compiled roughly half a million images of the sky each taking about 45s of exposure time. By correlating each image with its location on a standard celestial sphere, the researchers were able to stitch together this giant number of images into one map of the sky.


• 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!

• The highest recorded temperature on earth was 58°C in Libya in 1922.

• The lowest recorded temperature on earth was -89.6°C in Antarctica in 1983.

• The moon is roughly 27 per cent the size of the earth and has a surface gravity of about 16 per cent that of the earth.

• Sunlight can penetrate clean ocean water to a depth of 75m.

For more trivia see: www.um.edu.mt/think

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