Valmiki says Rama was born on a Shukla Navami. Distance between Sun and Moon is > 96 deg. He also says Sun is exalted which is in Mesha Rashi( 0 to 30 deg). The he says Moon is in Punarvasu Nakshatra which ends at 93.20 deg from beginning of Aries. So Navami and Punarvasu cannot happen as per the method our Jyotish calculations are done today. Is Valmiki wrong or the way we do jyotish math wrong. I would kindly call upon the jyotish experts on this site to throw some light on this.
Added the exact shlokas from Bala Kaanda chapter 18 below with translation given at valmikiramayan.net
ततो यज्ञे समाप्ते तु ऋतूनाम् षट् समत्ययुः |
ततः च द्वादशे मासे चैत्रे नावमिके तिथौ || १-१८-८
नक्क्षत्रे अदिति दैवत्ये स्व उच्छ संस्थेषु पंचसु |
ग्रहेषु कर्कटे लग्ने वाक्पता इंदुना सह || १-१८-९
प्रोद्यमाने जगन्नाथम् सर्व लोक नमस्कृतम् |
कौसल्या अजनयत् रामम् सर्व लक्षण संयुतम् || १-१८-१०
विष्णोः अर्धम् महाभागम् पुत्रम् ऐक्ष्वाकु नंदनम् |
लोहिताक्षम् महाबाहुम् रक्त ओष्टम् दुंदुभि स्वनम् || १-१८-११
8, 9, 10, 11. tataH yaj~ne samaapte = then, ritual, on completion; R^ituuNaam SaT sam atyayuH = seasons, six, well, passed by; tataH = then; dvaadashe maase = in twelfth, month; chaitre naavamike tithau = chaitra month [April-May], ninth, day;
nakshatre aditi daivatye = star of the day [punarvasu,] whose presiding deity is aditi;
panchasu graheSu swa uccha samstheshu = of five, planets, in their own, highest, positions - in their own cCha sthAna-s, viz., intheir own ascendent positions - meSha, makara, karkaTa, mIna, tula - rAshI-s;
chandra yukta guru karkaTa lagne proudyamane;
karkaTe lagne = in Cancer [of Zodiac]; vaak patiH= when Speech's, Lord [Jupiter]; indunaa saha = Moon, along with; pra udyamane == when raising - when ascendent; [abhijit lagna= advancing daytime];
kausalyaa = Queen Kausalya; jagat naatham = worlds', lord [Vishnu]; sarva loka namaskR^itam = by all, worlds, adored; divya lakshana samyutam = divine, attributes, along with;
viSNoH = Vishnu's; artham = epitome of [not half of Vishnu];
mahaa bhaagam = greatly blessed one; ikshwaaku nandanam = Ikshvaaku dynasty, delight of; lohita aksham = lotus-red, eyes; mahaa baahum = lengthy, armed; rakta oSTam = roseate, lips; dundubhi svanam = drumbeat, voiced; raamam = Rama as; putram = the son; ajanayat = gave birth.
On completion of the ritual, six seasons have passed by; then in the twelfth month, i.e., in chaitra mAsa, and on the ninth day of that chaitra month [April-May], when it is punarvasu nakshatra yukta navamI tithi, i.e., when the ruling star of that ninth day is punarvasu, for which Aditi is the presiding deity; and when five of the nine planets - sUrya, kuja, guru, shukra, shani are in ucCha sthAna-s, namely, when those planets are in ascension in their respective houses - meSha, makara, karkaTa, mIna, tula - rAshI-s; and when chandra yukta guru, karkaTa lagne - Jupiter in conjuction with Moon is ascendant in Cancer, and when day is advancing, Queen Kausalya gave birth to a son with all the divine attributes like lotus-red eyes, lengthy arms, roseate lips, voice like drumbeat, and who took birth to delight the Ikshwaku dynasty and adored by all the worlds, and who is the greatly blessed epitome of Vishnu, namely Rama. [1-18-8, 9, 10, 11]
Twice six months had rolled a way since the great sacrifice was over and, in the first month of the New Year, on the ninth day of the bright fortnight, the Lord of the worlds chose to take human form and sent down half of His essence as the son of Kausalya (thenceforth to be known as Rama), the world-honored One, the crowning glory ot the grand line of Ikshwku, and the sum of all perfections. The constellation Punarvasu, of which Aditi was the regent, was chosen to preside at his birth. The Sun, Mars, Jupiter, Venus, and Saturn were in ascension in their respective houses. Aries, Capricornus, Cancer, Pisces and the Libra, Jupiter and the Moon were in conjunction ; the rising sign was Cancer. And KausalyA, shone with unparalleled effulgence, even as Aditi when she gave birth to Indra, the lord of the Shining Ones, the Vajra-wielder. - C. R. Sreeniuasa Aiyangar, 1910.
By this configuration of stars the supreme merits of Rama are indicated. atra sa~Nvastara mukha uttaayaNa vasanta caitra maasa shukla pakSha deva nakShatra diva abhijit lagna puNya nakShatraad utkR^iShTa kaale karkaaTaka lagne uccasya graha pa~ncake guru candra yoge shrii raama utpattiH | tasya sarva utkR^iShTataam sakala kalyaaNa guNa abhiramataam sakala shiShTa aadraNiiya sampattim mahaa paraakramam ca suucitam |dharmaakuutam.