What exactly is gravity?
It has a lot of effects that we may not even think about
1. It gives us weight
Although your mass – the amount of ’stuff’ that you are made of – would remain the same wherever you are in the universe, your weight would vary considerably. Weight is a force determined by gravitational attraction. It’s the product of a large body’s ’acceleration due to gravity’ (g) and its mass. So, for example, if your mass – not weight – was 70kg and Earth’s g is 9.81m/s2, your weight would be 686.7 Newtons.
2. It causes objects to gravitate towards each other
Bodies with significant mass can influence one another across thousands of astronomical units, or AU (one AU being the distance between Earth and the Sun). It’s no surprise that planets close to the Sun should orbit it in a gravitational ’dance’. What is surprising is that so should a tiny dwarf planet like Sedna, which gets out to 936 AU.
3. It bends light
One of the strangest things about gravity is that it can bend the path of electromagnetic radiation, including light. The stronger a body’s gravitational field, the more pronounced the effect. Some of the most spectacular examples of this come from Hubble Space Telescope images of galaxy clusters – which have large concentrations of mass.
Light from more distant galaxies is distorted, as if by a lens.
4. It causes ripples in space-time
One of the most extraordinary discoveries of this century was the existence of gravitational waves, or ’ripples’ in space-time. These were detected by the Laser Interferometer Gravitational Wave Observatory, operated by Caltech and MIT, in September 2015 and are thought to have come from two colliding black holes 1.3 billion light years away. Although it was thought that gravitational waves could be detected from such an extreme event, no one had any idea when, or if, that would happen.
2. Galaxy cluster Galaxy clusters – particularly ones where galaxies are packed in – act as giant lenses. 1. Distant galaxyA distant galaxy that normally couldn’t be observed is about to be revealed. 4. Distorted light rays and lensed imagesLight rays from the galaxy are distorted and lensed by the cluster’s gravitational field. 3. Dark matterAlthough galaxy clusters contain an enormous amount of mass, gravitational lensing reveals invisible dark matter. 5. Telescopes and observers Observers on Earth can see the extent to which this gravitational lensing occurs.