What ex­actly is grav­ity?

It has a lot of ef­fects that we may not even think about

All About Space - - Gravity -

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.

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