How is this different from the NStars plot?
NStars is out of date and had 2633 components of 2011 systems (of which 1832 systems were reliable); this new database has 2804 components of 2090 reliable systems.
From the perspective of the actual plot, NStars had colors assigned by the spectral type of the system primary (aka, largest, brightest member of the star system) and uniform sizes; but it was also missing many spectral types.
This plot has colors assigned by the actual color (V-K, or green V filter brightness versus near-infrared K filter brightness) of the primary component of the system, and point sizes assigned by their absolute V magnitude (true brightness, measured as if the star were at 10 parsecs) compared to main sequence stars (normal stars) of the same V-K color. Thus, large points are giants, small points are subdwarfs, tiny points are white dwarfs.
What do the spectral types mean?
The sequence goes O,B,A,F,G,K,M,L,T and relates to temperature, hottest (O) to coldest (M). M stars are only red-hot, G stars are like the Sun, and O stars are blue-hot. There is a gradation here, there is very little different between an F9 and a G0 star.
Masses, brightness and number usually vary with spectral type too. M stars are the least massive, dimmest, and yet most common, while O stars are the most massive and brightest... but they are so rare there is only one B star within 25 parsecs (Regulus, 23.7 parsecs), and no O stars.
The L and T classes are for objects smaller than stars and larger than planets. They're very cool, very red, extremely dim, and (unexpectedly) rare.
There are also many white dwarfs within 25 pc, these are the dim blue-hot remains of dead stars. They are the small purple dots.
How many of these can I see?
All of the B, A, F, and G-type stars (blue to white) should be visible without a telescope from somewhere on the Earth. A few of the closest K stars (yellow) can be barely seen without a telescope, but you'll need one to see any of the M stars (orange/red). None of the white dwarfs, despite being blue-hot, can be seen either
Why are G stars white? And why are M stars orange?
I needed a smooth gradation of color that didn't go through green.
Also, G stars (like the Sun) ARE white, how else would a white piece of paper look white in sunlight? And M stars, like the M supergiant Betelgeuse, really do look orange, only becoming red when they're VERY cool and dim. As for the purple stars, I admit that's pretty much made up.
Why are the white dwarfs tiny violet dots now?
Because white dwarfs are HOT earth-sized cores of dead stars.
Why are there numbers flying around on their own?
Mistakes in the code. Either the system is so far under the main sequence that the dot was made too tiny to see, or my code accidentally made the star black, based on V-K color. Incorrect infrared K magnitudes could cause both of these.
Is this everything within 25 parsecs?
No. There are only 2090 star systems in this plot but 51 systems within 5 pc of the Sun. If we assume the space density is the same, there should be 6375 systems within 25 pc (Volume: 5x5x5=125). This is only 33% of what's probably out there, and you can SEE the other edges are less dense than the center of the plot.
On the other hand, we are reasonably sure this plot contains every system known as of the end of 2010 with a combined mean parallax greater than 0.04 arcseconds (maximum 25 pc) and an error less than 0.01 arcseconds (maximum 25% error). We are missing many components of binary stars, though.
Why do you count systems, not stars?
Current star formation theory expects that star systems form as systems, not as stars. One collapsing cloud = one mention here. On a more practical note, all the members of the multiple systems fall well within the plotted dots.
How was this made?
The RECONS database (made by the RECONS group at Georgia State University, more directly Dr. Todd J. Henry, Adric R. Riedel, Dr. Angelle M. Tanner, and Jennifer G. Winters), a custom IDL program, and The GIMP to assemble the frames.
May I use this image elsewhere?
Yes, but please credit A. Riedel and RECONS.
Can I get the list?
Not yet. We are not in any way done with this... At the moment the database is missing hundreds of known companions, and all kinds of other information we want to keep track of.
What's the huge yellow star?
I'm having trouble seeing it.
It's rotating clockwise, and viewed from 30 degrees above the equatorial plane.