When we look up at the night sky with the unaided eye, we see stars that are up to about 1000 light years away, depending on their brightness. We also see objects which are much closer, in our celestial backyard so to speak, which only reflect light from the sun like the moon, and the planets out to Saturn.
Beyond that we need increasingly powerful telescopes to see the outer planets Uranus and Neptune and what was for a time the planet Pluto, now a dwarf planet.
But with increasingly powerful telescopes both here on earth and in space as well as space probes and looking at the orbits of the planets and comets we’ve found that our solar system is actually much bigger than we thought but just how big may surprise you.
For thousands of years we’ve looked up at the night skies and seen the planets, Mercury, Venus, Mars, Jupiter and Saturn and that is what we thought the extent of it was, although back then we didn’t know that Jupiter and Saturn were much bigger but much farther away.
We also used to think that the earth was the centre of the universe and everything revolved around it including the sun, but these ideas were overturned with scientific observation and reasoning.
And it was with this reasoning, and the growing use of mathematics, our understanding of gravity and celestial mechanics that would suggest that there was more out there than met the eye.
With the creation of the telescope, the planet Uranus was discovered in 1781, and then a new planet was proposed and eventually discovered in 1846 using mathematical calculations to predict its position due to the perturbations seen in the orbit of Uranus. That planet was Neptune and with this new discovery, the size of our solar system, as in the distance from the sun to the new last planet, Neptune, had grown considerably.
We had now moved from discovering objects through just vision alone, to that of prediction using mathematical calculations.
Then in 1902, Percival Lowell suggested they could be a 9th planet after observing the relationship between the orbits of the planets and meteor showers as well as with comets.
In 1910 Lowell started his search for this elusive new planet and in 1911 he purchased a blink comparator, a specialised stereoscopic microscope that held two photographic plates side by side and a mechanical shutter that allowed the observer to alternate between the two images and highlight any differences between them.
Although Lowell was unsuccessful, 19 years later on Feb 18th 1930 Clyde Tombaugh using the same blink comparator and photographic plates from a 13 inch, 24 inch and 42 inch telescopes discovered what we now know as Pluto which became the 9th planet.
However, in 2006 the international astronomical union demoted Pluto from a planet to a dwarf planet because it could not meet one of the three criteria required for an object to be classed as a planet.
These were in that it had to orbit the sun, Which it did, it had to be spherical, which it was, and it must be big enough to clear its own orbit, which as it is located in the Kuiper belt which is filled with other objects and several of them are of a similar size, it did not.
I am never late, nor am I early, I arrive precisely when I mean to… so long and thanks for all the fish.
Something else which suggested that the solar system was actually much bigger than was first anticipated was the work done to identify comets which came through the solar system at regular periods and then disappeared back out into space.
It was realised that if these objects kept returning even after years or decades they must be on a very large orbit and therefore part of the solar system but where did they come from?
In 1755, Immanuel Kant, a German natural philosopher, suggested that the sun and the planets were formed from an extensive and diffuse nebula and that comets also must have come from this same material.
This was later expanded upon by the French scientist Pierre-Simon Laplace in 1805 when he published his celestial mechanics. However, he could not explain the highly eccentric orbits of comets nor the almost random directions in which they appeared to come from in the sky and suggested that they may be from outside our solar system.
But by the second half of the 19th century, astronomers discovered that the sun and the entire solar system moves through space within the milky way Galaxy. If that was so, and if comets were interstellar objects, then we would see more of them coming from the direction of the suns travel through interstellar space, which we did not.
It was the Italian astronomer Giovanni Schiaparelli that suggested that comets come from a uniform cloud that surrounds the sun at a much farther distance but which was still part of the solar system.
With the discovery of periodic comets, like the famous Halley’s comet, it was proven that comets were indeed just like planets on an orbit around the sun, although it was a highly elliptical one, rather than the mostly circular ones of the planets.
By observing their movement and using newtons laws, their orbits could be calculated to work out where they may have come from.
But it would take until 1950 when the Dutch astronomer Johannes Oort suggested that the solar system is surrounded by a huge cloud of material extending over a 1000 times farther out than the orbits of Neptune and Pluto.
This would be made-up of material which came from the original primordial nebula from which the sun and the planets formed, something that Immanuel Kant theorised 195 years earlier.
Oort demonstrated that as the sun moves around the Galaxy, stars passing near the outer boundary of this cloud might perturb some of these “would be” comets just enough to alter their orbits and send them into the inner solar system.
Here the sun’s heat would melt the ice in the comet’s nuclei creating the tails that give them their distinct appearance.
In 1951 another Dutch astronomer Gerard Kuiper, suggested that most of the short period comets were located in an area which started just beyond the orbit of Neptune which was later called the “Kuiper belt” and was first observed in 1992 and included the now dwarf planet Pluto and many other dwarf planets and planetoids which still to be discovered.
The size of the Oort cloud, although it’s never been actually observed because it’s too far away and the objects are too small and dark to be seen by even the most powerful telescopes we have, is now thought to extend up to about 1.5 light years from the sun in what is called the “hills sphere” or sphere of influence but could be upto 3 light years.
This is where the influence of the sun’s gravity is still stronger than that of the next largest body, namely other nearby stars.
The nearest star, Proxima Centauri a red dwarf is part of the triple star system Alpha Centauri and is 4.25 light years away but is only 12.5% of the mass of the sun, so its sphere of influence is a lot smaller but its nearby companions are sun-like stars and similar masses, so even though they a bit farther away that would increase their sphere of influence greatly.
To put this size into perspective with Voyager 1, the only man-made object to go beyond the heliopause where the pressure of the solar wind is equal to the pressure of the interstellar wind, it will take 300 years for Voyager 1 to reach the start of the Oort cloud and then another 30,000 years to cross it and exit it’s far side, meaning that our solar system is probably between two and four light years in diameter.
This would make our solar system between 10,000 to 20,000 times bigger than the orbit of Saturn, which was thought for hundreds if not 1000’s of years to be the limit of our own backyard, who knows what we might find in the future as look to explore this last part of our solar system.
So I hope you enjoyed the video and a big thanks go to our patreons for their on going support.
