Telescope is a Legends of Idleon NPC: quest reward, 1 quest.

Telescope | Idleon Toolbox

Telescope

Complete_all_constellations_in_the_Smolderin'_Plateau._You_can_check_your_progress_within_the_Telescope.

Complete_all_constellations_in_the_Spirited_Valley._You_can_check_your_progress_within_the_Telescope.

Hold down to add these gems to your account. You can then spend them in the Gem Shop!

Hold down to instantly get 2 Hour of AFK Gains.

Hold down to instantly get 4 Hour of AFK Gains.

Follow the engraving's advice, and press the little constellation on the bottom right branch.