This episode's question is: what is dark matter? If you have feedback or a topic suggestion you can email us.

This episode's question is: why do stars twinkle while planets don't seem to? Stuart explains that this has something to do with "astronomical seeing." If you have feedback or a topic suggestion you can email us.

This episode's question is: we know what the speed of sound is but what is sound speed? If you have feedback or a topic suggestion you can email us.

Occasionally, rather than asking a specific question, we ask Stuart why he finds something interesting. This episode's question is: what is interesting Craters? If you have feedback or a topic suggestion you can email us.

This episode's question is: what is the Drake Equation? If you have feedback or a topic suggestion you can email us.

This episode's question is a follow up to the Drake Equation episode: What is the Fermi Paradox? If you have feedback or a topic suggestion you can email us.

This episode's question is: does pretty much everything in our universe rotate and why? If you have feedback or a topic suggestion you can email us.

Occasionally, rather than asking a specific question, we ask Stuart why he finds something interesting. This episode's question is: what is interesting about Charon, one of the satellites of the dwarf planet Pluto? If you have feedback or a topic suggestion you can email us.

This episode's question is: how does the global positioning system, or GPS, work? If you have feedback or a topic suggestion you can email us.

This episode's question is: we understand that gravitational lensing is one of the predictions of Einstein's theory of general relativity but what is it? If you have feedback or a topic suggestion you can email us.