# Limits of space telescope?

Watching this video describing the "next generation" space telescope, it seems like the biggest mirror will be ~6 meters in diameter.

Theoretically, if a telescope was built in space instead of shipping it pre-built, and the mirror was, not a few meters, but a few kilometers, (and whatever other important aspects of a space telescope that a novice like myself has no idea about, multiply them by a few orders of magnitude) would it provide benefits proportional to the size difference?

• That is an incredible video, wow! I think it can serve as the basis of many many new questions here. Thanks for the link! – uhoh Dec 25 '20 at 21:55
• – uhoh Dec 26 '20 at 0:11

## 1 Answer

Yes, absolutely! The performance of any telescope depends on its diameter. A larger instrument not only collects more light, but also provides better resolution than a smaller instrument. The resolution limit is calculated from:

$$R_{arcsec}\ = {1.22\ \lambda \over D_{mm}}$$

whereas limiting magnitude is calculated from

$$L_{mag}\ =\ 2.5\ +\ 5\ log\ D_{mm}$$

I suppose there are eventual limits to $$R_{arcsec}$$, but I have never heard of any. As for limiting magnitude, as it’s a logarithmic formula, it grows very slowly as $$D_{mm}$$ increases, but a larger telescope is still a gain.

The whole thing is to balance $$R_{arcsec}$$, $$L_{mag}$$, and \$, of course!