Rahukaalam (also spelled as Rahukal or Rahu kalam) or the period of Rahu is a certain amount of time every day that is considered inauspicious for any new venture according to Indian astrology (Vedic).
In Hindu mythology, Rahu Kala is one of the 8 segments of the day and considered inauspicious period in Indian astrology due to its associated with malefic, Rahu . The segments are calculated by taking the total time between sunrise and sunset, at a given place, and then dividing this time duration by 8. Astronomically in the Hindu Panchangas, the ever varying planetary configurations mean that the auspicious hours during each day will not always fall at the same moment of time. Rahukalam and Yama Ghantam are the two time periods which are especially considered inauspicious or unlucky (Ashub).
The planets according to Indian astronomers were the Sun, Moon, Mars, Mercury, Venus, Jupiter, Saturn, Rahu and Ketu. Rahukaalam and Gulikaalalam are calculated based on these planets. Even though Rahu and Ketu are not physical bodies, they are sensitive points on the intersection of the ecliptic (the apparent path of motion of the Sun) by the Moon's orbit. Rahu is the northern point and Ketu is the southern point. Ancient astronomers felt that the mighty Rahu and Kethu have the strength to eat the sun, thus causing a solar eclipse. Hence it is considered inauspicious to begin any undertaking during this "Rahukaalam". Every day this Rahukaalam lasts for around 90 minutes, but the duration differs according to the length of the time between sunrise to sunset.
To calculate Rahukaalam, the time between the sunrise and sunset is divided into 8 units or time-groups, which time-group will have the Rahukaalam depends on the weekday.
Easy way to remember rahu kalam
Just remeber this phrase
"Mother Saw Father Wearing The Turban"
M(other)- 7:30 - 9:00 - MONDAY
S(aw) - 9:00 - 10:30 -SATURDAY
F(ather) - 10:30 - 12:00 - FRIDAY
W(earing) - 12:00 - 1:30 -WEDNESDAY
TH(e) - 1:30 - 3:00 - THURSDAY
TU(rban) - 3:00 - 4:30- TUESDAY
Left with Sunday - 4:30 - 6:00
ASSUMING THE SUNRISE IS AT 6:00 AM
Rahu Kalam Calculations
(E)leven (B)oys (H)ave (I)n a (G)ood (F)ootball (C)lub
Starting from MONDAY
E - 5th alphabet
5 + (5/2) = 7 1/2
Rahu Kala will be for 1 1/2 hours
So for Monday - 7 1/2 to 9.00am
B = 2nd alphabet
2 + 2/2 = 3
3 to 4 1/2 etc etc.