According to shastras, the whole universe is made of a 'material' called Narayana. Out of it, only 1/8th part is perceivable by us and it is called Vasudeva.The rest of Narayana cannot be perceived by ordinary mortals.
The names of the week from Monday to Sunday are so common place for us that we completely ignore their importance.This names are however not given randomly and are product of vedic astrology which has always been an integral part of Indian way of life since time immemorial.
Now let us come to the scientific astronomical facts - We all know that Saturn is the slowest moving planet and takes 30yrs to take a complete round and come back to original position.Then comes Jupiter 12yrs , then comes Mars, then Sun(geocentric) , then Venus, Mercury, Moon , in this order.First Hora(Hour) of the day , on any weekday, starts with the planet itself. Like on Saturday first Hora would be of Saturn itself then 2nd Hora of Jupiter, 3rd Hora of Mars ,4th Hora of Sun, 5th Hora of Venus, 6th Hora of Mercury and then the 7th Hora of Moon.(The sequence is according to their speeds as told above). Total One Hour each , we get 7 hours. Repeating the same sequence 3 times , we get 21 hours. But in a day, as we all know ,scientifically, there are 24 hours, so 3 Horas are still to go to complete a day. Here ending Hora was of Moon( 3 cycles - total 21 hours). So continuing with the same sequence we get 22nd Hour for Saturn, 23rd Hour for Jupiter, and finally 24th Hour for Mars. This completes the day of 24 hours.
Now taking the same sequence ahead, after Mars we get Sun, so the next day begins with Sunday. Same, the first hora of Sun , then, Venus, Mercury, Moon, Saturn, Jupiter and Mars.( one hour each).But as we know again 3 cycles are of 21 hours and 3 hours still to go to complete a day. Here also the ending Hora was of Mars , so continuing the same sequence we get 22nd hour of Sun, 23rd Hour of Venus, 24th hour of Mercury which completes the day. So the next in the cycle would be Moon .So the next day begins with Monday, the first hora of which would me of Moon itself.
Repeating one more time , we get , Moon, Saturn, Jupiter, Mars, Sun , Venus, and Mercury. ( 3 cycles complete 21 hours). So 22nd hour would be of Moon, 23rd of Saturn, 24th of Jupiter. (which completes the day of 24 hours). So next in the sequence would be Mars.Therefore ,the next day is Tuesday, which begins with first hora of Mars.
Likewise , if we continue, we would find that the sequence of the days of week are given very scientifically and logically by our seers and rishi's , who were very far ahead in science from any Eienstien or Newton.