looking at the solar system

[michel123456]

So I was fascinated by this simulator of the solar system on this site.

It shows evidently the result of the fact that the orbital speed of the outer planets is less than the speed of the inner ones.

The Average Orbital Speed of the Planets

As the planets orbit the Sun, they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion).

In the simulator I increased the speed to 2000 days/sec, put the viewer in zero projection (down right between the arrows), made a zoom out, and I was patiently waiting for all the planets to align. After a few minutes (only) my patience exhausted and I took the following screenshot where I draw roughly the alignment I expected to see:



Then I went on drawing the displacement of each planet following Keppler's law: the outer planets moving slower than the inner ones. And it goes like that:







Showing a spiral.

The spiral is not so obvious because there are not enough planets to see it clearly. If there were more stuff in between the planets, the image of the solar system would be like the one of a spiral galaxy.

Edited March 2, 2013 by michel123456

[BearOfNH]

Feb 5th, 1962 is often a good test date. Sun, Mercury, Venus, Earth, Jupiter lined up at the same time as a total solar eclipse. Mars and Saturn weren't too far away (15°) either. Many in the woo-woo community consider this day to be the start of the Age of Aquarius, for whatever that's worth.

[michel123456]

Yesterday I was looking at three years of Sun

 

 

In my profound ignorance, I was poundering:

We are rotating around the Sun. In 3 years, the video would have shown only 3 rotations. But there are obviously more, thus the Sun is rotating.

I went to the solar rotation Wikipedia page and indeed

 

Sidereal rotation

At the equator the solar rotation period is 24.47 days. This is called the sidereal rotation period, and should not be confused with the synodic rotation period of 26.24 days, which is the time for a fixed feature on the Sun to rotate to the same apparent position as viewed from Earth. The synodic period is longer because the Sun must rotate for a sidereal period plus an extra amount due to the orbital motion of the Earth around the Sun.

 

 

IOW the Sun makes a full rotation in 24.47 days, while the Earth needs one year to rotate around the Sun.

Which reminded me this thread.

 

The rotation speed increases towards the centre.

 

And I was thinking: the same law must apply inside the star. i mean, there is no reason why a physical law that applies between objects must not apply in the object itself. The law must apply everywhere, even if other forces apply.

 

So I was thinking that inside the Sun, the rotation rate must increase.

 

As it appears to happen inside the Earth, where the Earth's core is seemingly ratating faster than the crust.

 

http://www.columbia.edu/cu/record/archives/vol22/vol22_iss1/Core_Spin.html

http://news.nationalgeographic.com/news/2005/08/0825_050825_earthcore.html

 

 

 

[swansont]

 

Showing a spiral.

The spiral is not so obvious because there are not enough planets to see it clearly. If there were more stuff in between the planets, the image of the solar system would be like the one of a spiral galaxy.

 

No, it wouldn't. That's one of the problems that scientists have observed — galaxy rotation doesn't match up with the expectations from the visible mass. Your rotation spiral would "wind up" if you let it go longer, so that the inner bodies revolved more than once, and you'd lose the nice spiral you have. That's not what we observe. In a spiral galaxy, the outer stars rotate faster, implying there is more mass outside the central core region than we observe.

 

http://en.wikipedia.org/wiki/Galaxy_rotation_curve

[Janus]

To add to what swansont has said. The present understanding for the appearance of spiral arms doesn't have as much to do with these areas being full of stars and the gaps between them being empty as it does to what types of stars dominate in those regions.

 

The spiral arms represent density waves in the galactic material, they are something like "traffic jams" for the orbiting stars. It kind of like when you are driving along and you hit a slow down in traffic. the cars bunch together more, but once you leave the area they spread out again.

 

The thing about this bunching together with galaxies is that it tends to foster the birth of stars, so the spiral arms tend to be regions where stars are born. Now the more massive the star the brighter it is, but also the shorter it life span. The really bright stars will burn out before they ever get out of the traffic jam, meaning its is just the smaller dimmer one that ever make it to the "gaps" between the spiral arms. So basically,the reason that the spiral arms show up in contrast to the gaps between is just because that is where the really bright stars live out there lives. The gaps look dark not due to being empty, but due to the fact that being made up of the older dimmer stars.

[michel123456]

To add to what swansont has said. The present understanding for the appearance of spiral arms doesn't have as much to do with these areas being full of stars and the gaps between them being empty as it does to what types of stars dominate in those regions.

 

The spiral arms represent density waves in the galactic material, they are something like "traffic jams" for the orbiting stars. It kind of like when you are driving along and you hit a slow down in traffic. the cars bunch together more, but once you leave the area they spread out again.

 

The thing about this bunching together with galaxies is that it tends to foster the birth of stars, so the spiral arms tend to be regions where stars are born. Now the more massive the star the brighter it is, but also the shorter it life span. The really bright stars will burn out before they ever get out of the traffic jam, meaning its is just the smaller dimmer one that ever make it to the "gaps" between the spiral arms. So basically,the reason that the spiral arms show up in contrast to the gaps between is just because that is where the really bright stars live out there lives. The gaps look dark not due to being empty, but due to the fact that being made up of the older dimmer stars.

My remark is that in the solar system, the velocity of the planets is a function of the distance from the centre. It is a consequence of Kepler's law.

http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion

 

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

 

When the radius increase, the height of the triangle (the distance upon the orbit) must decrease.

 

I supposed the same happen in a galaxy.

[StringJunky]

To add to what swansont has said. The present understanding for the appearance of spiral arms doesn't have as much to do with these areas being full of stars and the gaps between them being empty as it does to what types of stars dominate in those regions.

 

The spiral arms represent density waves in the galactic material, they are something like "traffic jams" for the orbiting stars. It kind of like when you are driving along and you hit a slow down in traffic. the cars bunch together more, but once you leave the area they spread out again.

 

The thing about this bunching together with galaxies is that it tends to foster the birth of stars, so the spiral arms tend to be regions where stars are born. Now the more massive the star the brighter it is, but also the shorter it life span. The really bright stars will burn out before they ever get out of the traffic jam, meaning its is just the smaller dimmer one that ever make it to the "gaps" between the spiral arms. So basically,the reason that the spiral arms show up in contrast to the gaps between is just because that is where the really bright stars live out there lives. The gaps look dark not due to being empty, but due to the fact that being made up of the older dimmer stars.

Can you point me to any layman-friendly material online that goes into this spiral formation mechanism in certain galaxy-types a bit more? Thanks.

[MigL]

As swansont and Janus have pointed out, Michel123456, the fact that galactic rotation doesn't abide by Kepler's rule is what has prompted investigation into the 'hidden massive halo' around the galaxy.

 

So, Janus, when a large collection of stars, dust and gas, come together gravitationally, they form an irregular galaxy.

As it keeps collapsing, conservation laws ensure its rotational speed increases and central density creates a massive, active black hole. This would be the elliptical stage.

After several revolutions, the activity of the central black hole has subsided, and the 'traffic jams' that arise during the revolutions, have resulted in clearly delineated spiral arms where most of the stars, dust and gas are now located. This would be a 'mature' galaxy, and the spiral arms would get more and more pronounced with subsequent revolutions.

It does make sense.

 

However, I recall a type of galaxy called a 'barred' spiral, Where would such a beast fit in, and how would it arise ?

[Acme]

...

And I was thinking: the same law must apply inside the star. i mean, there is no reason why a physical law that applies between objects must not apply in the object itself. The law must apply everywhere, even if other forces apply.

 

So I was thinking that inside the Sun, the rotation rate must increase.

 

As it appears to happen inside the Earth, where the Earth's core is seemingly ratating faster than the crust. ...

There is differential rotation in the outer layers of the Sun that varies with latitude, while interior rotation is fairly balanced. It is this outer differential rotation that apparently leads to the solar magnetic pole shifts that are in sync with the 11 year sunspot cycle.

 

Differential rotation

Differential rotation of the Sun

See also: Solar rotation

 

On the Sun, the study of oscillations revealed that rotation is roughly constant within the whole radiative interior and variable with radius and latitude within the convective envelope. The Sun has an equatorial rotation speed of ~2 km/s; its differential rotation implies that the angular velocity decreases with increased latitude. The poles make one rotation every 34.3 days and the equator every 25.05 days, as measured relative to distant stars (sidereal rotation).

Internal rotation in the Sun, showing differential rotation in the outer convective region and almost uniform rotation in the central radiative region.

...

[StringJunky]

...However, I recall a type of galaxy called a 'barred' spiral, Where would such a beast fit in, and how would it arise ?

 

Barred Spiral Galaxy

 

Recent studies have confirmed the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts.^[8]

 

http://en.wikipedia.org/wiki/Barred_spiral_galaxy

[MigL]

Thanks for the link.

And thanks for not reprimanding me for not doing the search myself.

[StringJunky]

Thanks for the link.

And thanks for not reprimanding me for not doing the search myself.

That's alright. I learnt something new from it, . I didn't realise until today that most of the different galaxy forms are in fact various evolutionary stages of the same phenomena and the further away you look the greater the prevalence of one type of galaxy i.e. an earlier form.

Edited December 28, 2014 by StringJunky