... Tonight's Sky . ... Observing . ... Solar wind slowed by helium . ... L ike a sea anchor slacking the pace of a wind-driven ship, helium may be the drag that slows the solar wind in its million-mile-per-hour rush across the cosmos. ... The clues came from having a look at the rare times when the solar wind is at its slowest, only 600,000 miles per hour, when it is almost all hydrogen and hardly any helium." ... Only registered members of Astronomy.com are allowed to comment on this article. ...