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  A scientist investigating
space observes many
things. You use your
senses too to find out
about other objects,
events, or living
things.
  Scientists use process skills when
they investigate places or events.
You will use these skills when you
do the activities in this book. Which
process skills might scientists use
when they explore space?
  scientists classify
objects in space
according to their
properties. when
you classify, you
arrange or sort
objects, events
or living things.
  As they build satellites
and other machines,
scientists first estimate
the sizes of the various
parts, and then they
measure each part.