M3: Inconstant Star Cluster
Credit & Copyright: J. Hartman & K. Stanek (Harvard CfA)
Explanation: Star clusters appear constant because photographs of them
are frozen in time. In reality, though,
cluster stars swarm the center
and frequently fluctuate in brightness. Although the time it takes for stars to
cross
a cluster is about 100,000 years, the time it takes for a star to fluctuate
noticeably can be less than one night. In fact, the
above time lapse
movie of bright
globular cluster
M3 was taken over a single night. Most of the variable
stars
visible
above are
RR
Lyrae stars, stars that can quickly double their brightness while becoming
noticeably bluer. Furthermore,
RR
Lyrae stars vary their light in a distinctive pattern that allows unique
identification. Lastly, since
RR Lyrae
stars all have the same intrinsic brightness, identifying them and measuring
how dim they appear tells how far they are, since
faintness means
farness. These distances, in turn, help calibrate the
scale of the entire
universe.
Authors & editors: Robert Nemiroff (MTU) & Jerry
Bonnell (USRA)
NASA Web Site Statements, Warnings, and
Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service
of: LHEA at NASA / GSFC
& Michigan Tech. U.
