Shabbat HaChodesh: Shemini 5784
(א) וַיְהִי֙ בַּיּ֣וֹם הַשְּׁמִינִ֔י קָרָ֣א מֹשֶׁ֔ה לְאַהֲרֹ֖ן וּלְבָנָ֑יו וּלְזִקְנֵ֖י יִשְׂרָאֵֽל׃
(1) On the eighth day Moses called Aaron and his sons, and the elders of Israel.
ויהי ביום השמיני. לַמִּלּוּאִים; הוּא רֹאשׁ חֹדֶשׁ נִיסָן שֶׁהוּקַם הַמִּשְׁכָּן בּוֹ בַיּוֹם וְנָטַל עֶשֶׂר עֲטָרוֹת הַשְּׁנוּיוֹת בְּסֵדֶר עוֹלָם:

ויהי ביום השמיני AND IT CAME TO PASS ON THE EIGHTH DAY of the installation of the priests into their sacred office; this was the New Moon of Nisan on which the Tabernacle was finally erected, and it (that day) received ten crowns which are enumerated in Seder Olam.

אֲמַר לֵיהּ רַב חֲבִיבִי מָחוֹזְנָאָה לְרַב אָשֵׁי, תָּא שְׁמַע: ״וַיְהִי בַּחֹדֶשׁ הָרִאשׁוֹן בַּשָּׁנָה הַשֵּׁנִית בְּאֶחָד לַחֹדֶשׁ הוּקַם הַמִּשְׁכָּן״ — תָּנָא, אוֹתוֹ יוֹם נָטַל עֶשֶׂר עֲטָרוֹת: רִאשׁוֹן לְמַעֲשֵׂה בְרֵאשִׁית; רִאשׁוֹן לַנְּשִׂיאִים; רִאשׁוֹן לַכְּהוּנָּה; רִאשׁוֹן לָעֲבוֹדָה; רִאשׁוֹן לִירִידַת הָאֵשׁ; רִאשׁוֹן לַאֲכִילַת קָדָשִׁים; רִאשׁוֹן לִשְׁכּוֹן שְׁכִינָה; רִאשׁוֹן לְבָרֵךְ אֶת יִשְׂרָאֵל; רִאשׁוֹן לְאִיסּוּר הַבָּמוֹת; רִאשׁוֹן לֶחֳדָשִׁים.

Rav Ḥavivi from Ḥozena’a said to Rav Ashi: Come and hear: “And it came to pass in the first month in the second year, on the first day of the month, that the Tabernacle was erected” (Exodus 40:17). It was taught: That day took ten crowns. It was the first day of Creation (Sunday), the first day of the offerings from the princes, the first day of the priesthood, the first day of service, the first time for the descent of fire, the first time that consecrated foods were eaten, the first day of the resting of the Divine Presence, the first day that the Jewish people were blessed by the priests, and the first day of the prohibition to bring offerings on improvised altars, the first of the months.

הַחֹ֧דֶשׁ הַזֶּ֛ה לָכֶ֖ם רֹ֣אשׁ חֳדָשִׁ֑ים רִאשׁ֥וֹן הוּא֙ לָכֶ֔ם לְחׇדְשֵׁ֖י הַשָּׁנָֽה׃
This month shall mark for you the beginning of the months; it shall be the first of the months of the year for you.
החדש הזה. הֶרְאָהוּ לְבָנָה בְּחִדּוּשָׁהּ וְאָמַר לוֹ כְּשֶׁהַיָּרֵחַ מִתְחַדֵּשׁ יִהְיֶה לְךָ רֹאשׁ חֹדֶשׁ (מכילתא). וְאֵין מִקְרָא יוֹצֵא מִידֵי פְשׁוּטוֹ, עַל חֹדֶשׁ נִיסָן אָמַר לוֹ, זֶה יִהְיֶה רֹאשׁ לְסֵדֶר מִנְיַן הֶחֳדָשִׁים, שֶׁיְּהֵא אִיָּר קָרוּי שֵׁנִי, סִיוָן שְׁלִישִׁי:

החדש הזה — God showed Moses the moon in the first stage of its renewal, and God said to him, “The time when the moon renews (חדש) itself thus, shall be unto you the beginning of the month.” But no Scriptural verse can lose its plain meaning, so God spoke this in reference to the month Nisan: this month shall be the beginning in the order of counting the months, so that Iyar shall be called the second, Sivan the third.

דָּבָר אַחֵר, הַחֹדֶשׁ הַזֶּה לָכֶם רֹאשׁ חֳדָשִׁים, מָשָׁל לְמֶלֶךְ שֶׁנּוֹלַד לוֹ בֵּן וְעָשָׂה יוֹם טוֹב, וְנִשְׁבָּה אוֹתוֹ הַבֵּן וְעָשָׂה שָׁם זְמַן מְרֻבֶּה, אַחַר זְמַן נִפְדָה אוֹתוֹ הַבֵּן וְעָשָׂה לוֹ הַמֶּלֶךְ יוֹם גֶּנוּסְיָא, כָּךְ עַד שֶׁלֹא יָרְדוּ יִשְׂרָאֵל לְמִצְרַיִם הָיוּ מוֹנִים לַשִּׁעְבּוּד, מִשֶּׁיָּרְדוּ וְנִשְׁתַּעְבְּדוּ שָׁם, עָשָׂה לָהֶם הַקָּדוֹשׁ בָּרוּךְ הוּא נִסִּים וְנִפְדוּ, הִתְחִילוּ מוֹנִין לֶחֳדָשִׁים, שֶׁנֶּאֱמַר: הַחֹדֶשׁ הַזֶּה לָכֶם רֹאשׁ חֳדָשִׁים.

Another interpretation: “This month shall be for you the first of months” – it is analogous to a king to whom a son was born, and he made a celebration. The son was taken captive and was there [in captivity] for a long time. After that time, the son was redeemed, and the king made a birthday celebration for him. So, until Israel descended to Egypt, they would count toward the enslavement. Once they went down and were enslaved there, and the Holy One blessed be God performed miracles on their behalf and they were redeemed, they began counting the months, as it is stated: “This month shall be for you the first of months.”

החדש הזה לכם ראש חדשים. מכאן ואילך יהיו החדשים שלכם, לעשות בהם כרצונכם, אבל בימי השעבוד לא היו ימיכם שלכם, אבל היו לעבודת אחרים ורצונם, לפיכך ראשון הוא לכם לחדשי השנה. כי בו התחיל מציאותכם הבחיריי:

החודש הזה לכם ראש חדשים, from now on these months will be yours, to do with as you like. But in the time of slavery your time was not your own, but rather, they were in service of other people and their will. Therefore this will be first for you of the months of the year, for in it, you began your emergence into choice.

אבן עזרא
והנה אין ללבנה שנה כלל. כאשר אין לשמש חדש כלל. כי לא יתחדש בשמש דבר רק דבר החדוש הוא לאור הלבנה. ובעבור זה נקרא חדש. גם ירח. בעבור חדוש אור הלבנה כי אין לה אור בראיות גמורות. כי אם מהשמש. על כן לא תקדר השמש כי אם ברגע מחברתו עם הלבנה. אם היו בראש הטלה או בזנבו ולא תהיה קדרות ללבנה כי אם בהיותה לנכח השמש בלילה במקומות הנזכרים.
Ibn Ezra on Exodus 12:2
Now the moon has no year, as the sun has no month. Nothing new happens to the sun; only to the light of the moon does something new occur. It is because of this that a month is called a chodesh and also a yerach. It is so called because the light of the moon is renewed. We have conclusive proof that the moon has no light of its own, and that its light comes from the sun. The sun therefore does not darken except in the moment when it is in conjunction with the moon at the head or the tail of Aries. Similarly, the moon does not darken except when it is opposite the sun in the aforementioned places at night.
WHAT ACTUALLY CAUSES A SOLAR ECLIPSE?
As we now understand the phenomenon, a solar eclipse occurs when the moon gets in-between the sun and the earth. When it does, it blocks some of the sunlight and casts a shadow on the earth. A person standing in that shadow (called the umbra) will see an eclipse. The time at which the moon is directly between the sun and the earth is also the start of every Jewish month... And so it is clear that a solar eclipse can only occur on (or very close to) Rosh Chodesh, the start of the new Jewish month. However, we certainly do not witness a solar eclipse on every Rosh Chodesh. The reason is that the moon’s orbit is inclined at 5 degrees from the sun-earth plane, so that each month the moon may be slightly above, or slightly below that plane. An eclipse will occur only when the three bodies line up on the same plane, which only occurs infrequently.
WAS THE PLAGUE OF DARKNESS A SOLAR ECLIPSE?
Since we are only a couple of weeks before פסח, we will end with another look at an old theory, in which the Plague of Darkness was caused not by a miracle, but rather by a (conveniently timed) solar eclipse. In 1916 Eduard Mahler (d. 1945) suggested this explanation in his Handbuch der Jüdischen Chronologie, (Vienna 1887). According to Mahler, there was a solar eclipse visible in Egypt on Thursday March 13, 1335 BC. Since this was the only such eclipse, it would date the Exodus as occurring on March 27th, 1335 BC.
However, there's an obvious problem: the Torah describes the darkness lasting for three days. But a solar eclipse is over in a matter of minutes. Mahler has in interesting answer: instead of reading the verses (in Exod. 10) like this:
(22) there was a thick darkness in all the land of Egypt for three days. (23) They did not see each other, or get up from their places for three days.
read them like this:
(22) there was a thick darkness in all the land of Egypt. (23) For three days they did not see each other, or get up from their places for three days.
The eclipse lasted only a few minutes, but its effect on the Egyptians lasted three days. And what about the Jews in Goshen -why was there no Plague of Darkness there? Because they lived outside of the totality - the area in which the complete eclipse occurred - and would not have noted any significant darkening. Now there are some problems with this theory - like the fact that according to NASA, the solar eclipse to which Mahler referred seems to have been only a partial eclipse throughout Egypt. Still, it makes for a good discussion. Try that at your Seder Table.
Jeremy Brown, Talmudology
https://www.talmudology.com/jeremybrownmdgmailcom/tag/Solar+eclipse