Astroboffins discover Sun is surfing on 9,000-light-year gas wave that acts as Milky Way's stellar nursery The Milky Way's spiral arm that's home to our Solar System has been found to cradle the largest gaseous structure in the galaxy – a long, thin strip of jumbled star-forming matter measuring 9,000 light-years long and 400 light-years wide. A team of researchers published details of their discovery in Nature this week. Named the …
And now I have the Universe Song going round and round in my head.
My name is Two Gun Pierre
I wear rose buds in my hair
And a chic-chic pink bandanna round my neck
I came down from Tennessee
With a cowboy on my knee
And a pair of leather chaps around my legs ... hold on boys!
I was down in Cripple Creek
I was dying for a leak
So I dropped my pants behind a cactus there
When I fastened up my belt
I can't tell ya how I felt
But I knew the meaning of a prickly pear ... ouch!!
Oh I've got a cactus in my y-fronts and a vulture round my head
I've just been kissed by a Tennessee miss and I wish that I were dead
I've a jockstrap made of leather and pants of PVC (ee - ee - ee - ee - ee - ee)
The cactus in my y-fronts make a loser out of me!
In Californ - i - a
Where the rustlers are so gay
I bought a gentle gee-gee name of Jacques
But he livened up a lot
When he felt my prickly spot
And that buckin' bronco broke my buckin' back!
So I walked up to Nevada
Where the gals try so much harder
And I met a beefy belle called Caroline
But when she felt my prickles
She cried "Oh Lord, that tickles!"
And now she's run off with a porcupine
Oh I've got a cactus in my y-fronts and a vulture round my head
I've just been kissed by a Tennessee miss and I wish that I were dead
Do you like my high heeled horseshoes, I got them from Paree (ee - ee - ee - ee - ee - ee)
The cactus in my y-fronts make a loser out of me!
Alright horsey, hoof me a chorus
[tapping and neighing sounds]
Oh what a great hoof!
It's the yodelling coyote
[howling sounds]
Oh I've got a cactus in my y-fronts and a vulture round my head
I've just been kissed by a Tennessee miss and I wish that I were dead
I've got sequins on my saddle and I smell like a jasmine tree (ee - ee - ee - ee - ee - ee)
The cactus in my y-fronts make a loser out of me!
Icon - Anyone of a dozen reasons.
My brain doesn't work in a way that lets me understand even how the Sun's diameter and mass was discovered, there's usually an explanation about triangles and projection on a wall, but you'd have to know the distance to the Sun, and that's pulled out of a hat as well. And how can you calculate the Sun's speed? Anyway, if someone knows of a web site that explains this stellar stuff I'd appreciate it. It reminds me of how explanations of electrical circuits fall apart after the analogy to water in a hose and resisters are spigots and presto here's a multi-phase circuit diagram!
I think some of it started here-
https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion
and then Newton's theory of gravity. So starting with those assumptions lets you test the theories and solve for unknowns, ie if orbit = x then mass should be y. Wiki also has this history page-
https://en.wikipedia.org/wiki/History_of_gravitational_theory
showing it's still not completely solved, and space is frickin awesome.. Especially given the early pioneers got pretty close to our modern understanding with far more basic methods & observations.
We measure the distance from the Earth to the Sun using light and Jupiter's moons.
First, we find out how fast light is. Lots of fun with that. Of course, originally, we did not know that it was faster in a vacuum, but it it turns out that this does not make much difference. https://en.m.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatus
So, light travels at a bit over 186,000 miles/second.
The next thing we do is watch (and time) the orbits of Jupiter's moons. We find two things. First, that they obey Kepler's laws regarding their orbits. Second, that when Jupiter is in conjunction with the Earth, they appear to be slightly ahead, and when in opposition, slightly behind.
By how much? By the extra time that it takes light to traverse the distance between Earth when it is further from Jupiter (and its moons) than when it is nearer.
So we can measure the size of Earth's orbit around, and therefore distance from, the Sun in this fashion.
--
As for weighing the Sun, that is trickier. Newton's Law involve the gravitational constant (G), so if we know G, we can determine the Sun's mass from the period of Earth's orbit (now that we know it's size). But what is G? We make a guess. We guess that the Earth is basically granite, which does not compress. We know the Earth's size (which the Greeks worked out thanks to wells in Alexandria & Athens). We know granite's density. So, we have it's mass. We measure it's acceleration on objects to be 9.8m/s^2, so we can compute g to the accuracy of our guess as to the density of the Earth.
In 1798, the Earth was properly "weighed". See https://en.wikipedia.org/wiki/Cavendish_experiment
--
As for how fast the Sun is moving, that is even more fun. By the Theory of Gravity, the Sun is orbiting the gravitational center of the galaxy, but what does that even look like? First, we need to get some idea as to the size of the galaxy. The first rungs on the Cosmic Distance Ladder (https://en.wikipedia.org/wiki/Cosmic_distance_ladder) allow us to measure distances inside the Milky Way. We can use the Doppler Effect (https://en.wikipedia.org/wiki/Doppler_effect#Astronomy) to measure speeds as well, and combined, they allow us to figure out how fast things at our distance from the center of the Milky Way are orbiting.
Simples!
> In 1798, the Earth was properly "weighed". See https://en.wikipedia.org/wiki/Cavendish_experiment
The Schiehallion experiment took place 74 years earlier, with an less than than 20%.
So I'd never heard of the Schiehallion experiment. Or was aware that the experiment also spawned contour lines for cartography. Or even that the Royal Society had a Committee of Attraction. Or that pendulum clocks and gravity could be used as an excuse for being.. very slightly late. Or that you could weigh the Earth using just a handy Scottish mountain!
Quoting from the abstract:
"Remarkably, the new structure appears to be undulating and its three-dimensional structure is well described by a damped sinusoidal wave on the plane of the Milky Way, with an average period of about 2 kiloparsecs and a maximum amplitude of about 160 parsecs."
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