Monthly geek-out! Bear with me. A tenth planet has been discovered. "Sedna" is actually not really a planet, but it's the biggest thing that's been discovered since Pluto.

Someday I'm going to start a website that's all about trying to give a sense of size and scale to our universe, especially our solar system, with splashy diagrams and descriptive text. (And of course I would have to call it the Total Perspective Vortex, in honor of Douglas Adams.) In the meanwhile, here's some decidedly non-splashy graphics I whipped up that'll give you a sense of how far away this new object they've discovered is:

Se---j----s--------u----------n--------p-------------------------------
--q-@--------------------------------------------------------------------
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where
S is the sun
e is the earth
j is jupiter
s is saturn
u is uranus
n is neptune
p is pluto (on average)
q is quaoar
@ is Sedna, at its CLOSEST
! is Sedna, at its FURTHEST

Just how far away is that?

Have you ever seen a car with 186000 miles (300000 kilometers) on it? Imagine traveling all that distance -- every side street, vacation trip, work commute, whatever -- in a single second. That's how fast light travels. A (say) radio message traveling that fast would take over ten hours to reach Sedna at its closest point, and it would be another ten hours before you got a response. At its FURTHEST point, your message would take 117 hours (almost five days!) to reach Sedna.

Picture our moon; Sedna's about half as big, best guess. And at the distance it is out there, it's not going to be reflecting a lot of sunlight. It's amazing that they could spot this thing. The article doesn't say, but I'm sure it found near it's closest point in orbit, which it makes the rounds to every 10000 years or so. So, its last visit this close was around the time that agriculture and the bow and arrow were novel concepts.