Astronomy Day (Spring)
"For my part I know nothing with any certainty, but the sight of the stars makes me dream."
~ Vincent Van Gogh
This tartan, designed by Carol A.L. Martin, suggests the look of star photographs in deep space.
The colours in star photographs are usually a result of an additive combination of the emissions from specific electromagnetic wavelengths. Hot stars appear blue because most energy is emitted in the bluer parts of the spectrum. There is little emission in the blue parts of the spectrum for cool stars - they appear yellow and red.
A spiral galaxy like the Milky Way contains stars, stellar remnants, and a diffuse interstellar medium of gas and dust. The interstellar medium is typically composed of roughly 70% hydrogen by mass, with most of the remaining gas consisting of helium. This medium has been chemically enriched by trace amounts of heavier elements that were ejected from stars as they passed beyond the end of their main sequence lifetime.
If a cloud is massive enough that the gas pressure is insufficient to support it, the cloud will undergo gravitational collapse. Clouds start to shrink under their own gravity. As the cloud gets smaller, it breaks into denser clumps, starting a process which eventually yields a condition so hot and dense that hot and eventually becomes so hot and dense that nuclear reactions begin. When the temperature reaches 10 million degrees Celsius, the clump becomes a new star.
Shown above is the Serpens Cloud Core, birthplace of some of youngest groupings of stars in the Milky Way. The stars in question are in the very first stage of development, and in this image, they are represented by different colors: orange, red, and yellow. For more on star creation, click the stars!