The fourth day
A lot happened on the fourth day. The word רְבִיעִֽי (rebiy`iy fourth) is is a form of אַרְבַּע (arba` four). Both words are derived from רָבַע (raba` to lie stretched out). The usage of the derivatives may indicate that the verb is descriptive of four limbs stretched out.
And He set them
In the study of this day, the centrality of the earth is evident. In a special way (Hebrew: נָתַן nathan, to give) the vast heavens were "populated" especially for the benefit of the planet made for mankind.
The words introduced in these six verses were:
[ma'or] מָאוֹר luminary, lamp
['oth] אוֹת sign, signal
[mo`ad] מוֹעֵד appointed place or time
[shanah] שָׁנָה year
[galod] גָּדוֹל great, large
[qatan] קָטָן insignificant, small
[memshalah] מֶמְשָׁלָה rule, realm
[kolab] כּוֹכָב star
[nathan] נָתַן to give, set, put
[rabiy`iy] רְבִיעִי fourth, from רָבַע (raba` lie stretched out)