To me, “is astrology kosher” is like asking “is gravity kosher?” Astrology is a fact of life, as evident in the writings of all the Mekubolim: Sefer Yetsiroh, the Geonim, almost all the Rishonim, the Ramaq HaQodosh, the Ari HaQodosh, etc. The Midrash gives astrology as the reason for the extreme longevity of the pre-flood era generations: they were given long lives in order to be able to note the movements and effects of the stars.
The Ibn Ezra understands astrology to be topic of these famous words of Dovid HaMelech:
“The heavens declare the Glory of God; the skies proclaim the work of His hands. Day to day utters speech, and night to night tells knowledge. There is no speech and there are no words; their voice is not heard. Their line goes forth throughout the Earth, their words to the end of the world ...” 
The question really is ‘is the study or consultation of astrology permitted?’.
Until fairly recently, astrology was synonymous with astronomy and the Midrash and Talmud are clearly full of clear references to both. We had one example in Rashi a few weeks ago – see Rashi, Parshas Bo, ראו כי ראה נגד פניכם. There are plenty of allusions to astrology in the Zohar; see, for example, Parshas Bo, 42a. Reading it, one would be forgiven for thinking it a quotation from Ptolemy, or a medieval treatise on astrology. It isn’t. It’s Chazal.
Rabbi Akivo himself, who interprets the negative command of not to do divination as referring to astrology, was himself the recipient of astrological advice as can be seen in the famous story about his daughter on her wedding day. And his is not the only such story in the Midrash and Gemora.
Our culture and language clearly suggest that astrology is not foreign to Judaism. We regularly wish each other, “Mazal tov” and “zol zein mit mazal!”. Mazal means constellation (as in the Arabic manzal.) Sefer Chassidim and other classical works, even the Shulchon Oruch, are liberally dotted with minhogim and dinnim based on astrology. Some Amoroim and Rishonim were clearly experts in the field. The Beis Yosef goes to great length bringing the opinions of the Rishonim who were all of the opinion (except for the Rambam and Meiri) that astrology is a tool of G-d and its study is deep and profound. (This opinion is echoed in the works of the great and revered Acharonim such as the Vilna Gaon and the Ramchal.)
Yet, in his Shulchon Oruch, he is not so enthusiastic about astrology consultations. At first glance, this appears to run contrary to his high opinion of astrology so palpable in his Beis Yosef commentary on the Tur. Moreover, his very next halochoh in Shulchon Oruch is based upon astrological belief. On closer analysis however, it is clear that whereas he (in common with other Rishonim/Acharonim) permits the study of astrology and even to avoid certain situations that appear ‘inopportune’ due to ones personal foreknowledge of the stars’ influence, he advises against conducting ones life according to its dictates, in other words, consulting with astrologers in order to plan and direct ones affairs – according to the stars.
The reason for that is quite obvious when we consider for a moment what is meant by ד' הוא האלקים בשמים ממעל ועל הארץ מתחת אין עוד – “G-d is the Controller in the heavens above and on the Earth below; there is no other”. This means G-d arranges all the stars and constellations and therefore is the Author and Planner of all influences or reflections of states of being that can be found in the stars’ positions and aspects. We clearly and succinctly enunciate this in Ma'ariv when we say: G-d is מסדר את הכוכבים ברקיע כרצונו – “He arranges the planets and stars according to His Will”.
That is בשמים ממעל – in the heavens above.
However, we cannot and must not forget על הארץ מתחת – on Earth below He is also the Prime Controller, nothing happens without His Will. A person therefore, through his righteousness and resonance with the Will of G-d, can elicit a Divine ‘change’ in the general order and effect of the proposed influences.
Moreover, a Jew’s focus should be on G-d and fulfilling His Will. The stars are G-d’s tools. Why focus on the tools when we have access to G-d Himself?
There are several branches of astrology, natal – the study of the character, talents, etc, based upon the planets’ positions at birth, predictive and horary, which are divination tools, medical astrology and mundane astrology. Of these, natal, medical and mundane are clearly referred to by Chazal and Rishonim. The Ibn Ezra authored books on all these branches, including horary astrology, though it would appear that predictive astrology is forbidden, or at ,least run contrary to the Mitsvoh of תמים תהיה עם ד' אלקיך.
Astrology, as understood by Chazal, can help us understand a person’s character. It can also help us determine his predisposition to various ailments (this is unequivocally permitted according to the Shulchon Oruch – see Y.D. ibid. and commentaries ad loc.). All these are valid and permitted areas of study. These do not contradict our religious service – they may even enhance it. Natal astrology can show me my strengths, the talents G-d has given me in this lifetime to serve Him; medical astrology is like consulting a doctor – or better.
It is when we venture into predictive astrology that we run into danger. Though subject to dispute, most of even its strongest adherents will admit that astrology cannot accurately predict: it merely indicates likelihood or tendency; hence the Rambam’s total dismissal of the science (as a predictive tool) as it cannot be used with any accuracy. Astrology then can be seen to be the equivalent of a celestial meteorological office! Using it to predict the future understandably falls under the category of לא תעוננו (you shall not ‘divine’) which the Ibn Ezra etymologically connects with ענן – cloud, i.e. vague and unsure (though the Ibn Ezra disagrees with Rabbi Akivo’s interpretation).
Taking a critical look at Tanach, there appear to be no clear and indisputable pointers to astrology as a positive and praiseworthy study – not withstanding the opinions of the Ibn Ezra and Ralbag – but then mathematics and music are also not discussed! However, whereas the use of mathematics and music are mentioned several times in a laudable context, astrology is not. On the contrary, there are several pesukim that would appear to be criticising its use. On the other hand, as stated, it did find its way into the holy words of Chazal. In the Gemoro we find Chaldean astrology, in Zohar, Ptolemaic ideas, in Ramban, Vedic (Indian) astrology, etc.
That being the case, there should be some Scriptural source for its validation. I would point to two possible pesukim that seem to indicate the importance of astrology (even to the Nevi’im); one is in Tehillim, 147:4:
מונה מספר לכוכבים לכלם שמות יקרא
“He counts the number of the stars; He calls them all by name.”
and the other, a similar posuk, in Yishaiyeh, 40:26:
המוציא במספר צבאם לכולם בשם יקרא
“Who takes out their host by number; to all of them He calls by name … “
Both of these verses imply that stars have a Divine purpose and significance, not only as a collective body; each has a number, a name, a specific function connected with the Divine Plan. (In Egyptian astrology, these pesukim take on added significance; see first Rashi on Shemos.)
Bottom line: according to Chazal, astrology cannot predict. It can however be used for character analysis, in medical prognosis and as something one can be aware of in decision-making.
חכמה בגוים תאמין!
Regarding which school of astrology is ‘correct’ or more ‘kosher’, all the various schools appear to be reflections of an inner essence of truth – it makes no difference whether Western, Chaldean, Egyptian, Greek, Chinese or Vedic [though Vedic astrology does have connections with avoidoh zoro one should be wary of] – their varying modes of manifestation merely reveal facets of one enormous subject often interpreted according to prevalent culture, consequential outlook and place of emphasis.
 Psalms, 19:2-5.
 ויקרא יט:כו
 סנהדרין סה:
 Yoreh Dai’oh 179:2, Orach Chaim 271:1, Mogen Avrohom and commentaries ad loc., 551:1, to name a few examples.
 E.g. the Ralbag and Ibn Ezra. The holy Amoiroh, Rabbi Yehoshua ben Levi, was clearly an expert too.
 Y.D. 179
 Ibid. Se’if 1.
 דברים, י"ח, יג – See Y.D 179:1 Biur HaGra and commentaries ad loc.
 See Shabbos 156b, Zohar ibid.
 See for example דברים, ד יט
 See the quoted section in Beis Yosef, Y.D. 179.
 The author of this article has studied the Chaldean, Vedic, Medieval and Western schools, as well as the writings of Rishonim and Acharonim in this field.