Martin Luther’s attitude toward astrology included his appreciation for the difference between astrology and astronomy.
Astronomy is the oldest of all the sciences and has contributed to the progress of many arts; it was well known to the ancients, and especially to the Hebrews, who observed most diligently the course of the heavenly bodies...I praise astronomy and mathematics, which have to do with demonstrations [predictability], and I think that any star is greater than the earth, and that the sun is by far the greatest of the stars; for astrology I have no respect. [Preserved Smith’s translation of ‘Table Talk’ (1915, page 101-102)]
I am unable to admire sufficiently the human understanding for having observed with so great accuracy the orbits of the planets. [Preserved Smith’s translation of ‘Table Talk’ (1915, page 101-103)]
This is not to imply Luther had a sophisticated understanding of astronomy. He did not. Note his derision in 1539 of Copernicus, the now iconic astronomer who had postulated the earth and planets moved around the sun.
So it goes. Whoever wants to be clever must not be content with what any one else has done, but must do something of his own and then pretend it was the best ever accomplished. The fool wants to change the whole science of astronomy... [Preserved Smith’s translation of ‘Table Talk’ (1915, page 104)]
Copernicus (Polish, 1473-1543)
This offhand Table Talk bluster by Luther, based on hearsay four years before Copernicus published (and died), has been used frequently by the ignorant as ‘proof’ that Luther was hostile to science.
Philipp Melanchthon (1497-1460)
Martin Luther acknowledged astronomers could predict the paths of heavenly bodies and even the occurrences of eclipses. And though the difference between astrology and astronomy was occasionally blurred to him he had an aversion to astrology. This was not the norm for his time. Few nobles and bishops did not possess their astrologic predictions. Even Luther’s highly educated companion Philipp Melanchthon, 14 years younger, believed strongly in predictions made from astrology.
My Philip has devoted much attention to this business, but he has never been able to persuade me to accept it, for he himself confesses, ‘There is science in it, but nobody has mastered it, for astrologers have neither principles nor knowledge gained from experience, unless they wish to call something that happens experience.’ But knowledge gained from experience is derived by induction from many individual instances... [Luther’s Works, v. 54, ‘Table Talk’ (1967, page 173)]
Besides, astrology is not a science because it has no principles and proofs. On the contrary, astrologers judge everything by the outcome and by individual cases and say, ‘This happened once and twice, and therefore it will always happen so.’ They base their judgment on the results that suit them and prudently don't talk about those that don't suit. [Luther’s Works, v. 54, ‘Table Talk’ (1967, page 173)]
River Elbe at Wittenberg in 2006
Luther was at times exasperated with his friend Philipp.
Melanchthon kept me a day at Schmalkalden with his godless and shabby astrology, because it was a new moon. Once he would not cross the Elbe [river] during a new moon. [Preserved Smith’s translation of ‘Table Talk’ (1915, page 202)]
I regret that Philip Melanchthon adheres so strongly to astrology. He's very much deluded, for he's easily affected by signs in the sky and he's deceived by his own thoughts. He has often been mistaken, but he can't be dissuaded. Some time ago when I came from Torgau feeling quite weak, he said that I was fated to die then. I was never willing to believe that he was so serious about this business. I don't fear celestial signs, for our creation is above all the stars and can't be subject to them... [Luther’s Works, v. 54, ‘Table Talk’ (1967, pages 219-220)]
Another time Philipp did Luther’s horoscope. Luther exploded.
I don't care a fig about your astrology. I know and experience my [own] nature. [Luther’s Works, v. 54, ‘Table Talk’ (1967, page 449)]
In a calmer mood, Luther expounded on horoscopes (calendars) and his own supposed destiny.
There are many reasons I can't believe astrologers, and of these the principal reasons are the following: First, the calendars never agree. One astrologer prophesies that it will be warm, another that it will be cold. I think it should be understood that this is so: it's cold outside and warm behind the stove. Second, when a child is born, the rays of all the signs above the horizon or of all the planets or stars are said to reach that child. For the child is, as it were, a poppy seed in comparison with the smallest star. Now, I ask, why is it that all stars don't affect that child equally if all reach him equally? Third, why does the effect occur outside of the uterus, at the very hour and minute when the infant comes out of the uterus, and not in the uterus? Shouldn't the stars have influence in the uterus as well as outside of it? Do you mean to suggest that the stars care about a little skin on the woman's belly when otherwise the sun gives life to every member? Fourth, Esau and Jacob were born under one sign and in rapid succession. Where did the diversity of their natures come from? The astrologers rack their brains about this but they can't offer a solid explanation.
Thereupon somebody said, "Doctor, many astrologers agree that in the case of your horoscope the constellations that presided over your birth showed that you would bring about a great change."
[Luther answered] ...I set no store on this. You draw a conclusion from one, two, three, or four examples. What about the other hundred who were born the same hour under the same sign and don't have any correspondence at all with such advancement?" [Luther’s Works, v. 54, ‘Table Talk’ (1967, pages 458-459)]
Though Luther often argued against astrology with a crude scientific logic he also argued against it just as often because it was unbiblical. He was in no way a 'Renaissance man'.