The Maria Mitchell Association (MMA) honors America's first professional woman astronomer who believed that students learned best by doing real research projects. The MMA is dedicated to furthering science education, encouraging women in science, and serving as a science resource for Nantucket, MA. The mission is to increase knowledge and public awareness of the universe and the natural world through programs of scientific research and education. The Association celebrates its Centennial of the MMO (1908-2008) and the fiftieth anniversary of its outstanding undergraduate mentoring program. The program of supervised undergraduate research was initiated by Dr. Dorrit Hoffleit, the second MMO director, in 1957, and it has continued under the guidance of subsequent MMO directors - Drs. Emilia Belserene (1978-90), Eileen Friel (1991-96) and Vladimir Strelnitski (1997-present). Initially, the program was available only to female students; male students were first admitted in 1977, but the majority of the positions (two-thirds, on average) are awarded to females. The MMA is now a permanent NSF Research Experiences for Undergraduates site in astronomy. An analysis of the MMA astronomy alumni/ae career paths shows that the MMA's mentoring principles bring remarkable and ever improving results. In particular, the percentage of MMA astronomy alumni/ae attaining the PhD level increased from the (relatively high) value of approximately 20% in the first two decades of the program to about 60% in the last decade, this probability being now approximately equal for the male and female MMA astronomy interns - a remarkable and promising achievement, given the relatively small numbers of PhD-level women researchers and professors in American astronomy and physics. The extraordinary level of mentoring at the MMA is also seen from the fact that during the last decade, all the interns, without exception, completed their summer research projects, all presented the results, as a minimum, at a semi-annual meeting of the American Astronomical Society, and nearly three-quarters of them became authors or co-authors of papers published in refereed editions.
