Albert's Series: Basic stuff (R: ready, D: in development)
I. Short and simple Math notes:
II. Short and simple IT notes:
III. Somewhat larger (but simple) notes from Physics:
Quantum Mechanics and Interpretations:
SpaceTime, and Matter:
Other fun stuff:
The Sun's local neighbourhood.
Fig 1. The place of the Sun in our Milky Way.
About the figure: available from "https://en.wikipedia.org/wiki/Milky_Way" (Wiki media - public domain).
Figure 1, is a figure that shows the Milky Way as we probably would see it, viewed from
a position perpendicular to the disk (say, viewed from "above").
The Milky Way is a spiral galaxy, which is a galaxy with spiral arms containing stars, gas, and dust, in a rather flat disk.
The disk itself is believed to have a diameter in the order of 120000 lightyears.
Further, a spherical "halo" surrounds the disk, and contains mostly older stars and globular star clusters.
The whole system, is further believed to contain at least 100.000.000.000 stars.
The Sun (and it's Solar system), is located about 27000 lightyears from the center of the Milky Way, near the edge
of the Orion spiral arm.
It takes some effort maybe, but in figure 1, can you locate "Orion spur"? Close at that position, the Sun is located.
Astronomers continuously study the Milky Way, and discover details all the time.
I think that you already pretty much known all this sort of facts.
But what about the Sun's local neighbourhood? What does it "look" like (sort of)?
1. What does the Sun's local neighbourhood looks like?
Astronomers (due to various reasons) express distances rather in "parsec" than in lightyears.
In a local "bubble" of, say, 500 to 1000 lightyears across?
A "parsec" is very close to 3.26 lightyears, so if you see a distance listed in parsec, then just simply
multiply it with "3", to get a reasonably good idea of the distance in lightyears.
The "Local Bubble" is a sort of "cavity" in our local interstellar space, which has a radius close to 200 parsec
measured in the Galactic plane. Vertically, it's a bit larger.
Our Sun, is relatively close to the center of the Local Bubble.
Take a look at figure 2 below. It's a representation of the Local Bubble. If you would place that region
at the Sun's location in figure 1, then it would be a tiny fraction of a 1mm wide area (just to get an idea of the scale).
Indeed, figure 2 displays the "local neighboorhoud" of our Sun.
Some well-known stars are plotted in figure 2 as well, like "Sirius" (at a distance of 2.6 parsec, or 8.6 lightyears),
and "Arcturus" (at a distance of 11.3 parsec, or 36.7 lightyears).
Fig 2. Representation of the Local Bubble.
A large number of studies were performed on the Local Bubble, and research is still ongoing ofcourse.
From most studies, it can be found that the local bubble lacks the colder and neutral interstellar gas
of the surrounding "walls". Ofcourse, the transition from the cavity (the bubble) and the "walls" are not "abrupt",
but most astronomers themselves, address the "rim" of the surrounding intersteller matter as a "wall".
The closest dense and cold gas "wall", seems to have a distance from the Sun, close to 55-60 pc.
It seems to be still a matter of debate, but the cavity is characterized by a lower density, of hotter, and ionized gas.
Ofcourse, all "densities" are very, very low, and as we know, Space is primarily a "vacuum".
Also some "tunnels" to neighbooring cavities, through the surrounding denser interstellar matter (the "walls") are likely
to have be identified, although some debate over that subject takes place too.
One such neighbooring cavity, is called "the Loop I Bubble", located in the Orion Arm. It's rim starts roughly 100 parsecs
in the direction of the center of the Milky Way.
Figure 3 below, shows some of the "Loops" (cavities) near our own Local Bubble.
Fig 3. Representation of the Local "Loops" nearby our Local Bubble.
In figure 3, our own "Local Bubble" sits in the center.
Can you identify the star "Antares" in "Loop I"? This famous star is at a distance of 145 parsec,
or about 470 lightyears. This distance should give you an idea of the scale of figure 3.
The orange coloured regions in figure 3, are large "molecular clouds".
These are regions in the interstellar medium which are cold and dense enough for molecules to form.
These molecules are especially "H2", "Helium", and lower amounts of other molecules like "CO".
Often, those clouds contains a relatively higher amount of "dust grains" too, thereby seriously blocking background light.
It is believed that such regions can be associated with more concentrated star birth "places".
One such large cloud is the famous "Aquila Rift", visible in figure 3 too.
The Sun itself, has a speed of about 250 km/s around the center of the Milky Way. However all matter "turns" around
the center, but "tiny" variations across regions are simply a fact.
Presently, the Sun is in a smaller local cloud of denser Interstellar Gas. This small lump, is inside the Local Bubble.
You should be able to see that from figure 2.
There is some strong indications that the outer rim of this "smaller" local Cloud is only at a 4 ly distance.
The densities of Gas, and the temperature, is quite different between this "local lump" of Interstellar Gas, and
the average interior of the larger "Local Bubble".
Ofcourse, a question is what might happen if the Solar System enters the "true interior" of the Local Bubble.
One effect is a certain change in the socalled "stellar wind" through the Solar System, but other effects
are possible too. However, the Sun, the Earth, and the rest of the Solar System, are around for a very long time now,
(about 5 billion years) so, very large effects are not to be expected.
However, we simply do not know of the possible effects, and that is a great area of study and research.
Spurs, bridges and Spiral arms:
When you would browse through atronomical studies on the spiral arms, and related structures,
it becomes very apparent that the Milky way, including the spiral arms, is a very dynamic place.
The major pattern are the real spiral arms themselves, but many studies are about individual streams
of stars and dust, from and to various locations. Really incredable stuff.
Of some smaller arms, many astronomers have indications that they are actually "spurs" from and/or
to other larger arms. Also, various "bridges" between arms seem to have been observed.
The dynamics (or the physics), that lies behind it, seems not to be fully solved, but many articles
go into the details of observations and the possible theories.
As a simple remark on the observations of such structures: it's probably not uncommon in spiral systems, since if
you look at other spiral galaxies, you can often see those structures between larger "main" spiral arms.
Below are a few illustrations.
Fig 4. Two "wikipedia commons" pictures of the main Spiral arms of our Milky Way.
Note also the smaller "Orion arm" or "Local Arm", which contains the Sun (close to it's rim).
Note: This "arm" is also known as the "Orion–Cygnus Arm", but also as the "Orion Bridge", and
sometimes also as the "Local Spur" or "Orion Spur".
It's really facinating to Google on spiral galaxy images, and note the main spiral arms of those galaxies,
but watch the (presumably) various bridges and spurs too.
2. Some Graphical representations of Stars in the Sun's local neighbourhood.
Some static maps, and some interactive maps, of nearby stars to the Sun, are really great to watch.
Even if it was only for fun.
Here are a few links to several, relatively simple, (non commercial) maps:
An interactive map of 32 nearby stars (kisd.de).
A static map (2D) of nearby stars to the Sun (newsfrombree.co.uk)
A static map from wikipedia (wikipedia)
A static map of stars within 12 lightyears (atlasoftheuniverse.com)
A static map of stars within 50 lightyears (atlasoftheuniverse.com)
A static map of stars within 250 lightyears (atlasoftheuniverse.com)
An interactive map of stars and objects (in-the-sky.org)
The "chromeexperiments" (chromeexperiments.com)