The Milky way is itself is not simply one galaxy: recent work has shown that it has lured in and engulfed many smaller galaxies over time, integrating their stars into itself…The ingestion started when the Milky Way was younger and smaller than it is now and continues today.

Galactic archaeology / faint streams of stars left over from the ingestion of the Milky Way / fossils of our galaxy’s past

hierarchical structure formation: [the architectonics of the universe] [connect to Peirce’s view of how we learn about science] / the widely held theory that our galaxy started small and swelled in part by adding mass in large gulps.

baryonic matter (the stars, gas and dust, etc.) and dark matter


SDSS Sky Server – Why do stars have colors? / red /blue /yellow/ searching for patterns in the magnitudes / "ra" and "dec" give the star's position, "type" tells you whether it is a star or a galaxy, and u,g,r,i, and z are the star's "magnitudes."

YELLOW: ra132.80285 / dec11.87843 / typeSTAR /u15.08 /g14.31 / r13.48 / i13.20 /z12.60

BLUE: ra132.95811 / dec11.82530 / typeSTAR / u15.48 / g14.81 / r14.87 / i14.35 / z13.68

LITE BLUE: ra133.13217 / dec11.57466 / typeSTAR / u15.06 /g12.28 / r11.72 / i11.70 / z13.89

ORANGE/RED: ra133.14095 / dec11.61485 / typeSTAR / u21.56 / g19.10 / r17.69 / i16.54 / z15.92

YELLOW: ra133.28105 / dec11.56615 / typeSTAR / u17.06 / g15.19 / r15.20 / i13.88 / z13.53

BLUE: ra133.26962 / dec11.58480 / typeSTAR / u15.64 / g14.61 / r12.56 / i14.51 / z14.07

RED: ra133.54453 / dec11.23368 / typeSTAR / u21.90 / g19.58 / r18.07 / i16.94 / z16.30

RED: ra133.72252 / dec10.99935 / typeSTAR / u22.66 / g19.67 / r18.24 / i16.89 / z16.19

[color is the difference in magnitude between two filters] [Magnitude is a number that measures the brightness of a star or galaxy. In magnitude, higher numbers correspond to fainter objects, lower numbers to brighter objects; the very brightest objects have negative magnitudes.] [The sun has magnitude of -26. The brightest star in the Northern sky, Sirius, has magnitude -1.5. The faintest object you can see with your eyes has a magnitude of about 6]

The definition of magnitude m in terms of radiant flux F is: m = -log2.51(F/FVega) / The star Vega in the northern hemisphere constellation Lyra is used as the standard for the magnitude system, so FVega means the amount of light arriving at Earth in a given time from Vega / FVega is like the zero point in Celcius

. . .

light traveling through empty space / shorter wavelengths appear blue or violet, and longer wavelengths appear red.


All objects give off "thermal radiation" - light waves emitted from the random motions of atoms inside the object. As the atoms heat up, they move around more, and thus give off more radiation. As atoms heat up and move faster, the peak wavelength of their thermal radiation change / every object in the universe emits thermal radiation / different stars have different peak wavelengths of thermal radiation because they have different temperatures

Quantitatively, the relationship between temperature and peak wavelength of thermal radiation is:

lpeakT = 2.897 x 10 -3 m K, where lpeak is measured in meters and T is measured in degrees Kelvin
(273.15 K = 0 C = 32 F).