The Gemara (Shabbos 156) tells us that Avraham Avinu was incapable of having children because of his associated astrological influences. We are told that Avraham Avinu was considered to be under the astrological influence of Jupiter (צדק) and that its position in the west was inhibiting Avraham Avinu from having children. The Gemara then cites from Sefer Yeshayau (41:2),
"'מי העיר ממזרח צדק וגו"
“Who awakened righteousness from the east, etc.”
The word righeousness, צדק, can also mean Jupiter. The Gemara understands that Hashem placed Jupiter in the east in order for its influence to be a positive one for Avraham Avinu. Seder Olam (1) teaches us that Avraham Avinu was seventy years old at the time that Hashem joined with him in the everlasting covenant that is discussed in this weeks parsha, Lech Lecha (15).
Interestingly enough, the Gemara cited earlier tells us that the verse from Sefer Yeshayahu was Hashem’s response to Avraham Avinu when he asked Hashem about having children. This question of Avraham Avinu is found in this same chapter of Bereishis. Perhaps, this is why the chapter of Sefer Yeshayahu that contains its verse is read as the Haftarah for this portion of the Torah.
If one looks at Jupiter’s postion during that year 1744 B.C.E. (based on the chronology of Seder Olam) he will see that it was visible in the western portion of the sky, relative to the Sun (meaning it would be in the sky already at sunset, obviously it will rise and set throughout the night. Most celestial objects move from east to west on any given night) early in the year and then was too close to the Sun, so it was not visible for a duration of time. It became visible again, this time to the east of the Sun, just before sunrise, on October 6 (Julian).
What is fascinating about this event is that on this day, it was so close to Venus, that, to the naked eye, they appeared to be touching. To have these two objects touch is extremely rare (to come so close to touch can be hundreds of years in between instances for any given location), and such an event would be witnessed as a spectacular event. Venus is the brightest star in the sky (sometimes even confused with aircraft) and Jupiter is the second brightest. The two together would have been seen to be shining brilliantly in the east. Venus is also associated with fertility (see Ibn Ezra's Reishis Chachma) and this was the issue that Avraham Avinu was discussing with Hashem.
Another fascinating point is that this evening would have marked the night of Yom Kippur (based on actual lunar visibility, not calculation). As is noted by Rashi in Bereishis (15) some of the animal offerings of the covenant were symbolic of the Yom Kippur offerings, and many of those that were not, were still symbolic of offerings of repentance. We may not have a reference to this convenant being enacted on Yom Kippur, but the symbolism between the two is remarkable. Couple that with this extremely rare event occurring on that day, and one cannot help but wonder if this is what the Gemara meant when discussing Jupiter shining from the east.