6:30 am or show up at 1:00 at the Constitution Ave entrance and they have a limited number.
If you want same day tickets, you must be on their website at 6 am.... They go fast! That's how my husband and I visited earlier this week.
Tickets are free but they are released 3 months in advance on the website (I believe its the first Tuesday of the month). Or you can go online at 6 am the morning you want to go and you may lucky enough to get picked. I went online in April to get my tickets for this weekend
Tickets to the museum are free.'located on the Musum's website.
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