The Night Sky June 2019
Exactly 100 years ago an Einstein experiment took place during a solar eclipse of that year. It was devised to prove his theory that gravity can bend the fabric of space. The experiment confirmed that the light from a star behind our sun appeared to be displaced during the eclipse. This experiment proved conclusively that gravity does indeed stretch and contort the fabric of space.
This may seem very technical but some concepts are made much easier to understand when you have a visual representation of a very complex idea. This following visual representation is not perfect but works well up to a point. Here goes! Imagine space to be an enormous tough, rubber sheet with objects placed on top of it. We know that the universe is expanding so the surface sheet is enlarging but not the objects themselves that are positioned on the sheet; they simply become further away from each other. The objects such as gigantic suns, planets and moons which rest on top of the sheet, press down on it. The greater the mass, the more the indentation on the sheet, stretching the fabric downwards and including the surrounding area, like the fabric on a trampoline.
If you now try to roll a ball along this surface, it would be deflected by these indentations more so by large objects and less so by smaller ones. This is what happened in Einstein’s experiment. However, instead of it being a ball travelling along the surface, it was light from a distant star. Just as I finished my last article the hugely historic first picture of a black hole in a galaxy called M87 was published. The black hole is enormous and placed on our rubber sheet or trampoline would make a massive indentation. Indeed, light is not just bent slightly but can be seen helplessly spinning around the black disc at the ‘event horizon’. As it passes this point it is pulled in to the depths of this vast cavern where even light cannot escape. Yet another example of Einstein’s brilliance as he predicted the existence of black holes long before they were observed!
Large objects ‘warp’ space and to make it even more complicated they warp time too! That’s where this analogy is limited. Time slows down the closer you get to a massive object. Time passes more slowly on earth than onboard a GPS satellite as gravity has a lesser influence - about 1 second every 60 years. The clocks on board these satellites have to be corrected for this effect and show how this very abstract idea is used in an everyday application.
Bootes
The constellation of Bootes (The Herdsman) contains one of the brightest stars in the sky, Arcturus. A rich golden yellow and about the same mass as our own sun, it is in fact 27 times the diameter! It has swelled to this size as it is in its final stages of stellar evolution; a fate that awaits our own sun in 5,000 million years. The complete constellation cannot be seen in the southern hemisphere but here in the northern hemisphere we can see it all. Legend has it that Bootes was taught the secret of winemaking. He gave wine to some locals who killed him because they thought they had been poisoned! (I do remember making homebrew like that myself, but got away with it!)
You can find Arcturus by following the handle of the plough in a curve towards the southeast.
This month contains the summer solstice (21st June) where the sun reaches its high point on its path in our sky. This of course means it only gets very dark for a short period.
Jupiter is the closest to us on 12th June and with a pair of binoculars you can see its four largest moons. Apart from our moon it will be the brightest object in the night sky.
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