Farthest object in Solar system

So I'm wondering, what's the angular diameter of an object the size of 'Land's End to John O'Groats' when it's 15.5 billion kilometres/103AU away - and what's its apparent magnitude??

So I’m wondering, what’s the angular diameter of an object the size of ‘Land’s End to John O’Groats’ when it’s 15.5 billion kilometres/103AU away

Tiny 😉

Seriously though, the formula is α = 2*arctan(g/(2r)), where α is the angle, g is the real size and r is the distance [it doesn't matter what units you use for g and r, as long as they are consistent].

So, in this case, if g = 1000km and r = 15.5bn km, then α is about 3.7 x 10-6 degrees.

and what’s its apparent magnitude

Dunno that one... it would depend on the albedo of the object.

So basically, what you're saying is, it's not very easy to see.

On the basis of the xkcd cartoon below, unless I've slipped a zero this new object has an angular diameter on the surface of the earth of about 40cm...

So basically, what you’re saying is, it’s not very easy to see

At 0.01 arseconds! No 🙂

Neptune is 2.3 arcseconds... Pluto is 0.1... so this is 10 times smaller than Pluto!!

They must be using one of those cool telescopes from the John Lewis ads, then 😉