Thousands of Iranians gathered at the mausoleum of the Islamic republic's founder Ayatollah Ruhollah Khomeini in Tehran today to launch celebrations for the 40th anniversary of Iranian revolution.<br />''   <br />'' The ceremonies for the revolution started at 9:33 am (0603 GMT), the exact time that Khomeini returned to Iran and his plane touched down at Tehran airport in1979.<br />''  <br />'' Ayatollah Ahmad Jannati, head of the influential expert's assembly which appoints the supreme leader of the Islamic republic, delivered a keynote speech. <br />''  <br />'' On February 1 each year, Iran begins 10 days of celebrations to mark the anniversary of Khomeini's return from exile after the pro-Western shah fled Iran following widespread demonstrations.<br />