One of the lesser known Egyptian gods and goddesses, the daughter of Ra, Bastet (sometimes also called Bast) was the cat-goddess of the Lower Egyptian city, Bubastis. As an heiress to the sun god, she was the opposite of her twin, Sekhmet, and thus, personified the beneficial aspects of the sun. 
Typically Bastet was drawn with the face of a cat (as opposed to her twin, Sekhmet, who had the face of a lion). Often enough, as the patron goddess of pleasure and joy, she was associated with music and dancing, and was depicted with a sistrum in her hands.  As a result of her fondness for frivolity, her festivals (which were held in April and May according to the Stele of Canopus) were known even in Greece for their entertainment. Herodotus points out that her festivals were among the most favored of the Egyptian gods and goddesses and that thousands of people came to Bubastis each year to “get their party on”. (That last part was me).
Yet, she was not all fun and games. As the daughter of Ra (and though she was the non-violent twin sister), she was a fierce defender of her father, fighting with the snake, Apep, who tried to stop Ra’s journey through the Underworld.
If you covet Bastet and wear her cat-amulets so that she may protect you against evil spirits, then you want to pay attention to the days she’ll be particularly looking out for you, and the days where she woke up on the wrong side of the bed.
Favorable days are: (1) the tenth day of the second month of Akhet (September 9), as she is surely watching out for you on this of all days; (2) the fifteenth day of the fourth month of Akhet (November 13), as today is the feast of the twin sisters, Sekhmet and Bastet; and (3) the twenty-first day of the first month of Proyet (December 19), which is the day Bastet guards the red and black lands (Egypt).
The day where you might not want to step on a crack (and break your mother’s back), is the twentieth day of the third month of Akhet (October 19), as this is the day of Bastet’s going forth, and she is not very pleased about it.
Her name comes from the ancient Egyptian word, bes, meaning “fire”. And, as the twin to Sekhmet (the Mighty One), and the daughter of the sun, she was the embodiment of the aspects of heat and light which encouraged growth.
Because she is connected with the cat, whose eyes become full and very large during the full moon, ancient Egyptians held a similar view and connected Bastet with the moon. She was a lunar goddess. 
And, like most Egyptian gods and goddesses, the passage of time and dynasties muddies the water. In some myths she is associated with the goddess, Mut. In others, Bastet is said to be the personification of Isis.
 Gods and Myths of Ancient Egypt, Barnett, Mary. P. 85. (1986)
 Egyptian Mythology, Goodenough, Simon. P. 83 (1997)
 Ancient Egyptian Magic, Brier, Bob. P. 231-237 (1980)
 The Gods of the Egyptians, Vol. 1, Budge, E.A. Wallis. P. 441 (1904)
 The Gods of the Egyptians, Vol. 1, Budge, E.A. Wallis. P. 442 (1904)