A compound lens forged by two galaxies is helping astronomers get a bead on the Hubble Constant and dark energy.

Here are the best telescopes for deep space — gaze far into the night sky and see star clusters and rare objects like the elusive 'blaze star.' Be prepared for the Black Friday sales. The best ...

Catadioptric, or compound, telescopes incorporate a primary mirror coupled with a corrector lens placed at the front of the tube. The primary mirror's curve is ground to a simple shape ...