Learn German: Raumschiffe fliegen am weitesten.

The base adjective is weit (far). To make the superlative with am, we normally add -sten. However, because weit ends in a 't' sound, saying 'weitsten' would be hard to pronounce. So, German adds an extra e to make it am weitesten. You will see this rule applied to adjectives ending in -t, -d, -s, -z, and similar sounds.

Why do we use am here instead of just adding a normal adjective ending?

We use the am ...-sten form when the superlative describes a verb (how they fly) or stands alone after 'to be', rather than standing right in front of a noun (like 'the furthest spaceship'). Because am weitesten answers 'how do they fly?', it acts as an adverb, and adverbs in the superlative always take this am ...-sten structure.

Is Raumschiffe a compound word?

Yes! It combines der Raum (space or room) and das Schiff (ship). Like all German compound nouns, the gender and plural form come from the final word. Since the plural of das Schiff is die Schiffe, the plural of das Raumschiff is die Raumschiffe.

Why isn't there a Die before Raumschiffe?