In Parshat Lech Lecha, we find Genesis 15:5, a great verse for astronomical commentaries and homiletics, for fairly obvious reasons:

וַיּוֹצֵ֨א אֹת֜וֹ הַח֗וּצָה וַיֹּ֙אמֶר֙ הַבֶּט־נָ֣א הַשָּׁמַ֗יְמָה וּסְפֹר֙ הַכּ֣וֹכָבִ֔ים אִם־תּוּכַ֖ל לִסְפֹּ֣ר אֹתָ֑ם וַיֹּ֣אמֶר ל֔וֹ כֹּ֥ה יִהְיֶ֖ה זַרְעֶֽךָ׃

He took him outside and said, “Look toward heaven and count the stars, if you are able to count them.” And He added, “So shall your offspring be.”

The medieval commentator Radak, Rabbi David Kimchi, comments on this verse:

ויוצא אתו החוצה, באהלו באה לו הנבואה והוציאו מאהלו במראה הנבואה לחוץ לראות את הכוכבים, וכן ותבא אתי ירושלימה במראת א-להים (ויחזקאל ח’ ג’) ומתחלה אמר לו שיהיו כעפר הארץ ועכשיו אמר לו שיהיו ככוכבי השמים והכל דרך הפלגה, כמו שכתבנו, וגם כתבנו הדרש

“He took him outside” The prophecy came to him in his tent, and He took him [Abraham] out of his tent in a prophetic vision to see the stars.

Similarly,  in Ezekiel 8:3 “He brought me to Jerusalem in visions of God;” Initially He told him [Abraham] that they [his offspring] will be “like the dust of the earth,” now it is described as “as numerous as the stars in heaven.” Both statements, of course, have to be understood as exaggerations, as we pointed out already on 13,16. We also mentioned the allegorical explanations offered on that verse.

So, according to Radak, Abraham stayed inside his tent and saw the stars in a prophetic show while inside the tent – the world’s first planetarium!

Rashi has a similar comment, based on the Midrash:

דבר אחר הוציאו מחללו של עולם והגביהו למעלה מן הכוכבים, וזהו לשון הבטה מלמעלה למטה:

Another explanation: He took him out of the terrestrial sphere [or lit. “sphere of the world”, or the Universe] and lifted him above the stars. This explains the expression of הַבָּטָה, looking down from above (Gen. Rabbah 44:12).

The original of the midrash that Rashi cites, Genesis Rabbah 44:12, has even more to it:

ויוצא אותו החוצה

רבי יהושע דסכנין בשם רבי לוי: וכי מחוץ לעולם הוציאו, שאמר הכתוב: ויוצא אותו החוצה?! אלא, אחוי ליה שוקקי שמיא, היך מה דאת אמר: עד לא עשה ארץ וחוצות

אמר רבי יהודה בשם ר’ יוחנן: העלה אותו למעלה מכיפת הרקיע, הוא דאמר ליה: הבט נא השמימה, אין הבטה אלא מלמעלה למטה

And He brought him forth without — ha-huzah (xv, 5).

Joshua said in R. Levi’s name: Did He then lead him forth without the world, that it says, And He brought him forth without? It means, however, that He showed him the streets of heaven, as you read, While as yet He had not made the earth, nor the outer spaces — huzoth (Prov. vm, 26).

[Note: “Outer space”!!! This is not my own translation but that of Rabbi Dr. H. Freedman, B.A., Ph.D. and Maurice Simon, M.A. from the Soncino Ed. of Midrash Rabbah]

Judah b. R. Simon said in R. Johanan’s name: He lifted him up above the vault of heaven ; hence He says to him, Look (habbet) now toward heaven, habbet signifying to look down from above.

All of these different comments on the verse describe some form of planetarium-like “sky show” – in a prophetic vision, of course.

Ralbag, Rabbi Levi ben Gershon, has another interesting comment on this verse. He explains that in Abraham’s time people did not yet know the number of stars. Hence it must have seemed a very large number. This flows from the fact that in Ralbag’s own time – the middle ages – they did know the number of stars in the sky… or at least the number of visible stars in the sky.

In fact, ancient astronomers probably knew this number approximately as well as medieval astronomers did. The total number of visible stars in the sky is in, fact, not so huge; roughly about 9,000. (Ancient and medieval astronomers may have not known all the ones in the southern hemisphere, etc. but that would have been true for both eras.)

That being the case, how is God’s promise to Abraham so great? Perhaps that’s where the prophetic planetarium comes in. The actual number of stars in the sky – i.e. in the Universe – is far, far greater than the paltry number that are visible to the naked eye.

In our Milky Way galaxy, there are roughly 10¹¹, or one hundred billion, stars. There are roughly a similar number of galaxies in the known Universe. Multiplying those together yields an estimated 10²² stars – a truly mind boggling number! Now that’s a huge promise!

But in order to communicate that to Abraham, taking him outside his tent to look at the visible stars would be irrelevant. God had to show it to Abraham in a vision – like the way a planetarium show takes its audience on a ride through space that they could never have seen from Earth itself.

That’s God’s astronomical vision and promise to Abraham!