You can take your chances standing in line, but just go online and reserve your tickets so you can plan your trip ahead.
Get thru website
I went on a Friday around 10am and walked right in, no tickets.
They are not giving out tickets until january..yu can go stand in a line at 11am and get in that way..yu are not let in until 1pm
https://nmaahc.si.edu/visit/passes The site has instructions for advance ticket sales - first Wednesday of the month
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