Seeing stars

   

I’ve really been paying close attention to galaxies lately. There’s a lot to learn about them! This is a particularly big and beautiful classic spiral, NGC 3344, featured by APOD yesterday:

Although you can see scads of individual stars in this galaxy, they are only the brightest ones there. There are many more stars in that galaxy than there are pixels in this or any image, so it is literally impossible for them all to be represented in a photo. What we mostly see is blended light, the light of countless stars smudged together, and only the brightest (or brightest clusters!) show up as individual dots of light. The red blotches are vast star-forming regions, huge nebulae that each contain a minimum of many thousands of stars.

Even an insanely high-res picture couldn’t hope to capture all the stars, if we had the telescope for it. The highest resolution version of this image available is just 3905×3750 contains only 16.4 million stars… a drop in the galactic bucket. NGC 3344 is about half the size of the Milky Way, which contains 250±150 billion stars, so it probably contains an absolute minimum of a fifty billion stars (and that’s really lowballing it). You’d need an image of about 200,000 pixels square in order to represent that many stars on a one-per-pixel basis, and much much higher still for any meaningful detail. In fact, it would be so big that it would be visually meaningless to us, much larger than our field of view, like trying to take in a kilometre-wide painting.

The true limiting factor on our ability to visually resolve stars is galactic scale: we can either see the whole or a fraction of its parts, but never both at the same time.