The European Space Agency released the latest data from its Gaia spacecraft this week showing the positions of 1.8 billion stars in our galaxy and the directions they are moving. It is the latest in a series of measurements that go back almost a century, when a Canadian astronomer made the first discovery of the movement of stars in the Milky Way.
The universe is full of galaxies which show up as beautiful spirals or other odd shapes in telescopes, but there is one galaxy we don’t have a picture of and that is our own Milky Way. That’s because we live inside it and it is far too large to step outside and see what it really looks like.
Stand on the street outside your home at night and try to see the shape of your city or town. You can only see nearby lights from street lamps and buildings. To see the whole town you would have to fly above and look down from an airplane.
Unfortunately, there is no airplane — or rocket for that matter — that can fly high enough to get a view of the Milky Way. But astronomers have found other ways to determine its shape and motion through the cosmos.
Perspective from within the Milky Way
In 1918 the Dominion Astrophysical Observatory in Victoria, B.C., opened with what was, at the time, the biggest telescope in the world — a 1.83 metre diameter beast.
Between 1928 and 1935, Canadian astronomer John Stanley Plaskett used the telescope to measure the motions of stars in the Milky Way.
Plaskett was the first to show that the Earth is about two-thirds of the way out from the centre of a great pinwheel galaxy spanning 100,000 light years across and takes 220 million years to turn once.
That’s one big galaxy.
A modern perspective
The Gaia mission is the latest and most precise measurement of stellar motion in the Milky Way, including the path of our own Sun around the galactic centre. It also found a swarm of stars above and below the main disc that could be the result of a collision with another galaxy hundreds of millions of years ago.
The information gathered by Gaia, which will continue its survey for another four years, will form a fundamental knowledge base that will be used to study galactic evolution and the forces that keep them together.
While 1.8 billion stars is an impressive number, it is only about about one per cent of all the stars in the galaxy, so there is still a long way to go before we get a complete picture of our city of stars.
This long quest to know our home galaxy is also testament to Canada’s contribution to astronomy, which has been at the forefront for more than a century.
The instrument that Plaskett used is still operating today, and you can even take a virtual tour of it. Canadian astronomers continue to work with it and other major telescopes around the world.
Understanding our place in the galaxy
Knowing the true nature of the Milky Way may not seem to have much relevance here on Earth, and it certainly won’t affect the weather tomorrow, but it is part of our long search to know our place in the universe.
It’s taken centuries to discover the shape and size of planet Earth, to develop the technological prowess to see it from space, and to make robotic explorers to explore the other planets in our solar system. During that time we’ve also been finding our place in the galaxy and the universe.
It’s fundamental science — knowledge for the sake of knowing — and that has never been a bad thing.