From the Massachusetts Turnpike I-90, take Exit 18 at Cambridge, and turn left onto Soldiers Field Road. Take the Harvard Square exit, bear right across Anderson Bridge, and drive straight into Harvard Square. Merge with Massachusetts Avenue, keeping Harvard Yard on your right. Stay to the right at the fork, and drive into the underpass. After the tunnel, turn left onto Quincy Street and, after one block, left again onto Kirkland Street. Kirkland ends at the Science Center; turn right onto Oxford Street. Here is visitor parking info, along with visitor permit FAQs and more directions & maps.
The 20-30 minutes drive from Logan Airport to Harvard Square can cost about 40 dollars.
One option: the Silver Line connects Logan Airport with South Station. Change there to the Red Line, stay six stops, and exit at the Harvard Station. This is a 1/2 hour ride. Another option: the shuttle bus at Logan stops at the Blue Line. Take the Blue Line inbound and exit at Government Center. Change to the Green Line westbound and go one stop to Park Street. Switch to the Red Line outbound in the direction Alewife, stay four stops, and get off at Harvard. Here is a map of the Boston subway system; for more information, visit the MBTA website.
From the Harvard Station, enter Harvard Yard, pass the statue of John Harvard, and walk toward the Science Center (the modern white staircase shaped building with two telescope domes on the top). Come into the main entrance and take the elevator to the seventh floor. Here is a campus map.
The current weather in Boston can be found here.