Lois & Clark Forums Forums Fan Fiction Fanfic Related Shape and size of Nightfall

In the latest installment of her fic Nighttime in the Daytime, Artemis says a little about the size and shape of Nightfall. I thought it would be interesting to compare Nightfall, which, if I got things correctly, would be 1.7 miles across, with the size of a few other "heavenly bodies". Also, I thought it would be interesting to consider the most likely shape of Nightfall.

Let's begin by looking at one of astronomy's favorite solar system denizens, Saturn's moon Enceladus. Enceladus is remarkable because it is as bright as freshly fallen snow, and still more interesting, it is actually releasing plumes of water ice and water vapour into space! This is an image of the remarkable water vapour plumes of Enceladus:



Fascinatingly, Enceladus is a quite small object. Here you can see the true size of Enceladus compared with the size of Great Britain:



For those of you not familiar with the actual size of Great Britain, this is what Wikipedia says about the size of Enceladus:

It could fit comfortably into Arizona or Colorado, eh? That's small for a moon. Its mean diameter is 505 kilometers, or 314 miles. That means that its dimeter is almost 185 times the diameter of 1.7 mile-sized Nightfall.

Enceladus is spherical, round, or pretty much round. That's not a given, necessary thing when it comes to small moons or asteroids. In fact, whether a moon or an asteroid is spherical or not has everything to do with its size and mass. A body which is massive enough will pull itself into a spherical shape because of its self-gravity. 314-mile Enceladus, however, is just a bit bigger than a moon or asteroid has to be in order to make itself spherical. According to Wikipedia, all the moons of Saturn which are smaller than Enceladus are also non-spherical, all except one, Mimas, whose diameter is about 400 kilometers, or 250 miles.



Mimas. Wikipedia says:

So anything smaller than Mimas can be expected to be non-spherical. The diameter of Mimas would be about 150 times larger than that of Nightfall.

Here are some astronomical bodies which are a lot larger than Nightfall, but which are nevertheless non-spherical:



At top, you have asteroid Gaspra, at bottom left, Martian moon Deimos, and at bottom right, Martian moon Phobos. Wikipedia says this about the size of Phobos:

27 x 22 x 18 km would be about 17 x 14 x 11 miles. Clearly Phobos is a lot bigger than Nightfall. It is also more irregular than it looks in this picture.

Phobos rotating

This is asteroid Ida:



Ida is much larger than Martian moon Phobos. The dimensions of Ida are 53.6 × 24.0 × 15.2 km, or 33.5 x 15 x 9.5 miles.

Take a look at the picture of Ida again. Can you see a tiny "pebble" to the right of Ida? That "pebble" is Ida's own moon, Dactyl. Dactyl is about 1.4 kilometers across, about 4,600 feet, less than a mile. So I guess that Dactyl is about half the size of Nightfall.

Ann

Solar bodies larger than 200 miles. Mimas being 3rd from the end.

Wow, cool picture, d. I've bookmarked it for any future reference I might need.

Artemis

Indeed, that's a great picture!

Ann

Asteroid Lutetia just had her picture taken. Here's the link: http://www.esa.int/export/SPECIALS/Rosetta/SEM44DZOFBG_0.html
Enjoy!
Artemis