Here are some words related to space and astronomy.
stjarneðlisfræði - astrophysics
stjörnufræði - astronomy
dulstirni - quasar
fljúgandi furðuhlutur - Unidentified Flying Object
fylgihnöttur - satellite
fylgitungl - moon
gervitungl - artificial satellite
geimfari - space traveler (e.g. astronaut)
geimþoka - nebula
halastjarna - comet
reikistjarna - planet
smástirni - asteroid
sól - sun
stjarna - star
svarthol - black hole
tungl - moon
utanjarðingur - extraterrestrial, alien
vetrarbraut - galaxy
þyngd - gravity
Jon