Berakhot 150

1:
In the Gemara [Berakhot 58b] the great Babylonian Amora Shemu'el boasts that "the paths of the heavens are as clear to me as the paths of Neharde'a" (his home town): in other words, he claims that he is well-versed in astronomy. However he admits that he does not know what a comet is. Obviously, Shemu'el and and all his contemporaries knew what a comet is, so we must understand his admission to mean that he could not explain the nature and composition of a comet. Maimonides, in his mishnah commentary, leaves no doubt: he defines a comet as something that looks like a star but has a hairy tail.

2:
I have translated "earth tremors" on the basis of Maimonides' commentary: he defines this term as referring to when a loud sound is heard reverberating in the air "like a giant millstone turning very slowly". The Gemara [Berakhot 59a] also identifies this term with the loud sound associated with earthquakes.

3:
Thunderclaps are explained by Shemu'el and the rest of the sages [Berakhot 59a] as being caused by clouds colliding in the sky (so they did know a thing or two about physics).

4:
Stormy winds presumably would include meteorological phenomena such as tornadoes, hurricanes and so forth.

5:
The common denominator of all the above is that they are natural phenomena that inspire fear and dread – and not only in more ancient breasts! The fact that we know what causes earth tremors, tornadoes, thunderclaps and so forth does nothing to alleviate our fear – not only of their appearance, but also of the damage they can cause. The berakhah defined by our Mishnah is designed to assure the person reciting it that all these phenomena are part of the natural world, part of God's creation. To the religious mind they are all physical expressions of God's "power and might". Modern scientific knowledge can detract nothing from the impressive message of this berakhah: all the myriad mechanisms of the universe reflect the enormous power and wisdom of God "whose merest thought created the heavens" [Psalm 33:6].

6:
Later developments in halakhah have elaborated on the more simple formula of our mishnah:-

1. the berakhah upon seeing a comet is defined [Shulĥan Arukh, Oraĥ Ĥayyim 226:1] as being "Praised be … in Whose universe that's the way things are".
2. That same source agrees with our mishnah as to the text of the berakhah over the phenomena of earth tremors, thunderclaps, lightening and stormy winds – but adds that a permissible alternative text is "Praised be … Author of Creation". Later custom seems to have categorized two of these phenomena: over thunderclaps the original berakhah is prescribed and over lightening flashes the latter. (Perhaps it would be worthwhile for us to revert to the original opinion of the Shulĥan Arukh – that there is a valid alternative: that would at least force people to think about their personal philosophy of natural phenomena.)

7:
The Amora from Eretz-Israel, Rabbi Yehoshu'a ben-Levi, adds a further berakhah. He says (as interpreted by later colleagues) [Berakhot 59a] that when it has been raining all night and the clouds are blown away in the morning and a clear sky is seen – one should recite the berakhah: "Praised be … the Author of Creation".