One translation for karma is 'work'. Suppose you have to make a shirt. There is a number of processes, a number of stages. The cotton has to be gathered from the field; it has to be cleaned and spun into yarn; then the yarn has to be woven into cloth and dyed. In the same way a man has to be made a knower of the Atman(self) through a series of rituals. Karma has to be performed in such a way as to purify him both outwardly and inwardly. Such a karma is called samskara.

That which removes the impurities from an object, takes away all the bad or evil elements, and imparts good qualities to it is samskara. For instance, certain types of samskara are conducted for the land: First the land is allowed to dry in the sun, then it is plagued and irrigated. Seeds, say, of paddy, are sown and after they sprout the seedlings are transplanted. The weeds are removed, the field irrigated again and the excess water drained off. When the corn is ripe, the crop is harvested, threshed and the chaff winnowed. The paddy has to be "seasoned" and pounded before the rice is used..As you can see Samskara is much more than a ritual performed once in a while every daily action in the Vedic Culture is done according to the Samskaras.

Now the connection between Samskaras and Astrology is that all the Samskaras are to be done at an auspicious time,place, and circumstance. That calculating of the proper time is known as Muhurta and is a branch of Jyotish.