O.C. 227:1 indicates saying בא"ה אמ"ה עושה מעשה בראשית on seeing זיקין (Mechaber describes this as a meteor; Mishnah Berurah surmises that this may be a comet.) The same blessing is suggested for seeing lightning.
Obviously (no pun, intended, here) this means if one sees these with a naked eye. What if one sees any of these via binoculars or through a telescope? Would he make the bracha, then?
I read this article. The author cites an article written by Rabbi J. David Bleich in Contemporary Halachic Problems v.1 (p.213-5) who discusses this question. I clicked the link which displays Google books, but most of the answer is not displayed. The rest of the authors article says that he asked his own (anonymous) rav who told him, you would make a bracha using binoculars; questionable if with a telescope.
That's all I was able to find. As the rav was not listed, and the author of the article is unknown, I'm wondering if there is a more reliable definitive answer to this question.