Is a blessing recited upon seeing a solar or lunar eclipse?
No. One is not to say any blessing, including the blessing of Oseh Maaseh Bereishis.
 Igros Kodesh 15:260 [printed in Shulchan Menachem 1:355]; Orchos Rabbeinu p. 95
 The reason: The Sages never established a blessing for an eclipse. No Poskim record that a blessing should be recited for an eclipse. Seemingly, the reason the Sages did not establish a blessing for an eclipse is because it is a bad omen, and requires prayer to nullify it and not a blessing. [Igros Kodesh ibid]