All nine. It has become common in the past few decades to appoint potential future Supreme Court justices to the US Court of Appeals Circuit Courts for development and to create a record of their jurisprudence for later evaluation.
Sonia Sotomayor is the only current justice with prior judicial experience on both a US Court of Appeals Circuit Court and a US District Court.
Federal judges on the US Supreme Court are called justices.
Someone
Life
Someone
True (:
The Senate confirms both federal judges and Supreme Court justices.
Federal (US) Supreme Court judges are called "justices." The Supreme Court of the United States has one Chief Justice and eight Associate Justices, for a total of nine justices. State supreme court vary in the number of judges seated on their highest appellate court, and are also inconsistent with titles. Some states call them "judges," while others refer to them as "justices."
Federal are often elected by voters or appointed by the president without approval of congress. Supreme Court judges are appointed with approval of congress and are on the court until they retire, die, or impeached.
Executive
True
True
Executive Branch.