Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2015 January 6
100 Million Stars in the Andromeda Galaxy
Image Credit: NASA, ESA, J. Dalcanton, B. F. Williams, L. C. Johnson (U. Washington), PHAT team, R. Gendler
Explanation: What stars compose the Andromeda galaxy? To better understand, a
group of researchers studied the
nearby spiral by composing the largest image ever taken with the
Hubble Space Telescope. The result, called the
Panchromatic Hubble Andromeda Treasury (PHAT), involved thousands of observations,
hundreds of fields, spanned about a third of the galaxy, and resolved over 100 million stars. In the
featured composite image, the
central part of the galaxy is seen on the far left, while a blue spiral arm is prominent on the right. The brightest stars, scattered over the frame, are actually
Milky Way foreground stars. The
PHAT data is being analyzed to
better understand where and how stars have formed in
M31 in contrast to our
Milky Way Galaxy, and to identify and characterize Andromeda's
stellar clusters and obscuring dust.
Tomorrow's picture: In the Arms of NGC 1097
