According to Ramayana 1.18.8,9
Rama was born on the 'Navami Tithi' of 'Shukla Paksha' of 'Chaitra Masa' (9th day of the increasing phase of the moon in the loonar month of 'Chaitra'). At the time the naxatra was 'Punarvasu' and Sun, Mars, Saturn, Jupitar and Venus were in Aries, Capricorn, Libra, Cancer and Pisces respectively. Lagna was cancer and Jupiter and moon were shining together.
[and many say this repeats every 10,000 years]
So the conditions summarized are as follows
Valmiki has recorded in Bal Kaand Sarga 19 and shloka 8 and 9 (1/18/8,9) that Shri Ram was born on the ninth tithi of Chaitra month when the position of different planets vis-a-vis zodiac constellations and nakshatras (visible stars) was as under :- 1 Sun in Aries ii) Saturn in Libra iii) Jupiter in Cancer iv) Venus in Pisces v) Mars in Capricorn vi) Lunar month of Chaitra vii) Ninth day after no moon viii) Lagna as Cancer (Cancer was rising in the east) ix) Moon on the Punarvasu (Gemini constellation & Pollux star) x) Day time (around noon)
Rama was born on the 'Navami Tithi' of 'Shukla Paksha' of 'Chaitra Masa' (9th day of the increasing phase of the moon in the loonar month of 'Chaitra'). At the time the naxatra was 'Punarvasu' and Sun, Mars, Saturn, Jupitar and Venus were in Aries, Capricorn, Libra, Cancer and Pisces respectively. Lagna was cancer and Jupiter and moon were shining together.
[and many say this repeats every 10,000 years]
So the conditions summarized are as follows
Valmiki has recorded in Bal Kaand Sarga 19 and shloka 8 and 9 (1/18/8,9) that Shri Ram was born on the ninth tithi of Chaitra month when the position of different planets vis-a-vis zodiac constellations and nakshatras (visible stars) was as under :- 1 Sun in Aries ii) Saturn in Libra iii) Jupiter in Cancer iv) Venus in Pisces v) Mars in Capricorn vi) Lunar month of Chaitra vii) Ninth day after no moon viii) Lagna as Cancer (Cancer was rising in the east) ix) Moon on the Punarvasu (Gemini constellation & Pollux star) x) Day time (around noon)
This data was fed into the
Planetarium software. The results indicated that this was exactly the
location of planets/stars vis-a-vis zodiac constellations on January10,
noon time in the year 5114 BC. As per the Indian calendar, it was the
ninth day of Shukla Paksha in Chaitra month and the time
was around 12 to 1 noontime. This is exactly the time and date when Ram
Navmi is celebrated all over India till date.
source : http://www.tribuneindia.com/2003/20031012/spectrum/main6.htm