Explain SYSDATE vs SYSTIMESTAMP and the session time zone

SYSDATE and SYSTIMESTAMP return the database server's clock. SYSDATE is a DATE — resolution of one second, no time-zone information. SYSTIMESTAMP is TIMESTAMP WITH TIME ZONE with fractional seconds and the server's zone. CURRENT_DATE and CURRENT_TIMESTAMP instead return the time in the session's time zone (ALTER SESSION SET TIME_ZONE). LOCALTIMESTAMP is the session-zone time without the zone component.

SELECT SYSDATE,
       SYSTIMESTAMP,
       CURRENT_TIMESTAMP,          -- session time zone
       LOCALTIMESTAMP,
       SYSTIMESTAMP AT TIME ZONE 'UTC' AS utc_now
  FROM dual;