In last week’s episode of It’s Okay To Be Smart, I talked about why the moon orbits the Earth. If you haven’t watched it yet, give it a look. I’ll wait.
There’s some pretty interesting and counterintuitive astrophysics keeping the moon orbiting Earth and not getting gobbled up by the sun. But I left one thing out of that video. The moon doesn’t really orbit the Earth. Strictly speaking, the moon and the Earth orbit each other.
Just like the Earth exerts a gravitational force on the moon, the moon and its mass are “tugging” right back on us. As a result, the two bodies are actually orbiting a point in between, called the barycenter.
If you’ve ever watched pairs figure skating, you’ve seen this in action. When spinning through this move, called a “death spiral”, the two skaters are actually rotating around a barycenter in between their two centers of mass:
This is true of any two orbiting objects, whether it’s a pair of binary stars, a planet and its star, or a planet and its moon(s). You can think of it just like a playground see-saw, with the masses and distance between the two orbiting objects determining where the “balance” point is.
The Earth/Moon barycenter is about 1,700 km beneath the crust:
Jupiter, despite being more than five times farther from our central star than Earth is, is so massive that its barycenter lies outside of the Sun:
The Earth-Sun barycenter, on the other hand, is effectively in the center of the sun. Our mass is just peanuts compared to that of that huge burning ball of hot gas:
When two orbiting bodies have similar masses and are relatively close to each other, it can be tough to figure out who’s orbiting whom. This is one reason that some astronomers think Pluto and its moon Charon are more of a double-dwarf-planet system:
Scientists use the see-saw physics of barycenters to study planets in distant solar systems, observing these wobbly waltzes to discover planets that we can’t see with telescopes.
The dig deeper into this cool bit of astrophysics, check out this article from my friend Chris Crockett. And cue the Dead or Alive…
Neil knows what's up
The twins of the stellar world are binary star systems.
A binary star is a star system consisting of two stars orbiting around their common center of mass.
When two stars appear close together in the sky as seen from the Earth when viewed through an optical telescope, the situation is known as an “optical double”.
This means that although the stars are aligned along the same line of sight, they may be at completely different distances from us. This occurs in constellations; however, two stars in the same constellation can also be part of a binary system
Binary star systems are very important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated.
This also determines an empirical mass-luminosity relationship (MLR) from which the masses of single stars can be estimated.
Also,it is estimated that 75% of the stars in the Milky Way galaxy are not single stars, like the Sun, but multiple star systems, binaries or triplets.
This is true. Sirius (aka the Dog star) - the brightest star in the sky is actually a binary star system.
When it was discovered in 1844 by the German astronomer Bessel, the system was classed as an astro-metric binary, because the companion star, Sirius B, was too faint to be seen.
Bessel, who was also a mathematician, determined by calculations that Sirius B existed after observing that the proper of Sirius A (the main star) followed a wavy path in the sky, rather than a uniform path.
Sirius can now be studied as a visual binary because, with improving technology and therefore improved telescopes, Sirius B was able to be seen, although not for 20 years after Bessel had correctly predicted its existence.
Hell Yeah! The term “binary system” is not used exclusively for star systems, but also for planets, asteroids, and galaxies which rotate around a common center of gravity.
However, this is not a trick question; even in star binaries, the companion can be a black hole.
An example of this is Cygnus X-1.
Definitely! A binary black hole (BBH) is a system consisting of two black holes in close orbit around each other.
In fact the LIGO experiment which confirmed the existence of Gravitational waves was able to acquire its data when two Binary Black Holes Collided and merged into one. This phenomenon sent ripples in the fabric of space-time which we call as a Gravitational Wave.
The Universe is amazing huh?
If you found this interesting, check out:
A Denied stardom status - Jupiter
Black Holes are not so Black (Part 3) - Gravitational Waves
Ganymede: Orbits Jupiter, Diameter 5,262 km
Titan: Orbits Saturn, Diameter 5,150 km
Callisto: Orbits Jupiter, Diameter 4,821 km
Io: Orbits Jupiter, Diameter 3,643 km
The Moon: Orbits Earth, Diameter 3,475 km
Europa: Orbits Jupiter, Diameter 3,122 km
Triton: Orbits Neptune, Diameter 2,707 km
Titania: Orbits Uranus, Diameter 1,578 km
Rhea: Orbits Saturn, Diameter 1,529 km
Niles, my spiritual guide, my idol
somewhere out there, there’s a star born the exact same day and time as you were
Time lapse of Voyager 1′s approach to Jupiter
Rings and Moons Circling Uranus, taken by Hubble space telescope.
js
Just a socially awkward college student with an interest in the celestial bodies in our universe.
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