The picture shows today's XKCD comic.

Transcript:

[A grayed-out sentence in the Times New Roman font reads "Optimistic aliens measure space typographically". The "O" in "Optimistic" is dark black and indicated as representing the Sun (not to scale). The dots of the letters "i" in the sentence are similarly dark black. The dot in the first "i" in "Optimistic" is indicated as representing Mercury; the dot in the second "i" represents Venus; the dot in the third "i" represents Earth. The dot in the "i" in "aliens" is indicated as representing Mars. The dot in the "i" in "typographically" is indicated as representing Jupiter. A measurement bar indicates that the distance between the "O" and the third "i" in "Optimistic" is equivalent to 1 AU (astronomical unit).]

[Caption below the panel:] 
Space tip: if you're ever lost in the inner Solar System, you can just type out the phrase "Optimistic aliens measure space typographically" in Times New Roman and use the dots as a map.