These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.20 s (backtrack: 0/20).

[ebuild  N     ] dev-lang/cfortran-20210827-r1::gentoo  USE="-examples -test" 101 KiB
[ebuild  N     ] net-libs/llhttp-9.4.3:0/9.4::gentoo  40 KiB
[ebuild  N     ] virtual/fortran-0-r1::gentoo  USE="openmp" 0 KiB
[ebuild  N     ] dev-libs/libgit2-1.9.7:0/1.9::gentoo  USE="ssh -examples -gssapi -test -trace" 7588 KiB
[ebuild  N     ] sci-astronomy/wcslib-8.3-r1:0/8::gentoo  USE="tools -doc -fits -fortran -pgplot -static-libs" 3170 KiB
[ebuild  N     ] sci-libs/cfitsio-4.7.0:0/10-r1::gentoo  USE="bzip2 -curl -test -tools" 2113 KiB
[ebuild  N     ] sci-libs/gsl-2.7.1-r3:0/27::gentoo  USE="deprecated -cblas-external -static-libs" 7346 KiB
[ebuild  N     ] sci-astronomy/gnuastro-0.16-r1:0/1::gentoo  USE="threads -static-libs" 5948 KiB

Total: 8 packages (8 new), Size of downloads: 26301 KiB