Meteor Rock vs Cygnus Yellow

How close are they?

ΔE 27.1, loose: different enough that you should pick on purpose. Cygnus Yellow is noticeably lighter, more saturated, cooler than Meteor Rock.

Can I use Cygnus Yellow instead of Meteor Rock?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Cygnus Yellow is noticeably lighter, more saturated, cooler than Meteor Rock.

Can I use Meteor Rock instead of Cygnus Yellow?

The same difference applies the other way round: Meteor Rock is noticeably darker, more muted, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.