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A compilation of old and new observations from Japan revised some important physical measurements of the Sun in the galaxy: According to the results, the Sun is orbiting the galactic center a little faster and, more interestingly, is closer to the Galaxy. center than previously thought.
Hey, there’s a supermassive black in the center of the Milky Way! Is it a problem?
Nope. The most recent distance measurement before this put us about 26,600 light years from the center. The new one is 25,800. It’s only about 3% closer, and we’re still a long way from the black hole.
If that makes you feel better, it’s about 260 quadrillion kilometers – 260,000,000,000,000,000. A bit of a hike. We are safe.
The new measurements come from a technique called radioastrometry – using radio waves to measure distances to objects. In this case, they used parallax: the apparent motion of an object as the Earth revolves around the Sun. As I wrote before:
To sum up, as the Earth moves around the Sun, we see nearby objects from a slightly different angle (like holding your thumb and blinking one eye and then the other; your thumb appears to be moving back and forth. compared to more distant objects.). We know how large Earth’s orbit is, so measuring the angles of movement of stars gives us their distance if you apply a small trigger.
I’ll go into more detail in the “Distances” episode of Crash Course Astronomy, if you like.
This idea is simple in theory but difficult in practice, because when the Earth revolves around the Sun, the Sun is orbiting the center of the galaxy, and other objects are also orbiting around it, all moving at different speeds. It’s a little tricky to sort out, but it helps that at some distance from the galactic center things tend to move at about the same speed. Combining this with where they are in the sky helps measure their distances and speeds; you have to take into account their position in their orbit and from what angle we see them. It’s like watching race cars go around a track: some seem to be heading towards you and others, depending on where they are, even though they are all going at the same speed.
You need extremely high resolution to make these measurements, and the astronomers in this case have used VERA: Exploration of Radioastrometry by Very Long Baseline Interferometry (or VLBI). This is an array of four 20-meter satellite dishes across Japan, using a very sophisticated technique to combine their power as if it were a telescope with a dish the size of their footprint at across the island. They are spread over 2000 km, so that makes a large telescope.
They observed masers: like lasers, but these emit microwave energy instead of visible light. This is produced in the gas clouds where stars are born. The water or methanol molecules in the clouds are pumped with energy by the young stars that form there and re-emit that light in a very powerful way. These objects can be clearly visible throughout the galaxy, making them very useful for radio astrometry. Astronomers have used 224 objects from old and new observations to map all the locations and speeds of objects around the galactic core.
When all of this is done (aided by a physical model of the rotation of the galaxy) the distance between the Sun and the galactic center can be found, as can its angular velocity (like, how long it takes to make 360 ° around the galaxy, which is an orbit).
The distance calculated in the new work, 25,800 light years, is indeed closer than the older measurements, although consistent with them given the measurement uncertainties. Most methods reach around 26,000 light years.
Measuring the speed of the Sun in its orbit around the Milky Way is more complicated (if it’s even possible), but in the end, they reach a speed of 239 kilometers per second. It’s pretty fast! But the gravity of the galaxy is strong, and it takes a zippy star to orbit it.
The International Astronomical Union, the official custodian of astronomical and other names and numbers ™, lists the distance and speed of the Sun as 27,700 light years and 232 km / s. These were adopted as standards in 1985, and things have changed a bit since then. Most of the distances measured are smaller, although the speeds tend to hover around this value. But assuming the new work is correct, the Sun is actually nearly 2,000 light years closer to the center of the Milky Way and moving 7 km / s faster.
Be careful, the sun is not much closer and does not move much faster than before! We’re just getting better measurements of what he’s actually doing.
By the way, using these new numbers, it means that it takes the Sun 219 million years to circle the galaxy once. This is sometimes called the Galactic or Cosmic Year. This number is smaller than previous estimates (ranging from around 230 to 250 million years ago), as the new work gets closer to the center of the Milky Way (and therefore to a smaller orbital circle) and a speed slightly higher.
This number is of limited scientific use, but it’s interesting. Plus, my friend and astronomer Jessie Christensen realized that this means dinosaurs lived on the other side of the galaxy!
In fact, it’s a little more complicated than that because the entire galaxy is moving at all different speeds, mixing things up. But conceptually, it’s pretty cool and gives you an idea of how long ago (and how long!) Dinosaurs were there, and how big the galaxy is.
And how complicated Apparently simple things can be.
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