The first big event at the beginning of the year is the Department Picnic which is usually held at Adelphi Mills Park. Besides the food and games and the mingling, the highlight of the picnic is the annual faculty/grad student volleyball match which the graduate students have now lost for 3 years in a row!
In the fall, there is a wonderful party at the Leventhal's home. This catered affair brings together many Washington area astronomers and department faculty, staff and students. Good food, good wine and good dessert.
In October, the University and Goddard Space Flight Center host the Maryland October Conference. It is a small (attendance 100-200) meeting with a well-defined topic of interest. The talks are generally quite good, and there is ample time for discussion both in the sessions and during breaks. The food is fantastic, and all meals/cocktails/etc. are included with your registration. Graduate students are expected to help with organization, registration, and microphones/slides during the presentations. In exchange, the department pays your registration fee. It's a great deal.
In the fall, we have the Grand Astronomy Assembly, which is called to order by the Grand Poobah. All courtiers and subjects (i.e. faculty/postdocs/students) are expected to attend to listen to the State of the Department address. The winners of the TA of the Year award and the John Wang Memorial Award are announced at this time. Concerns may be aired at the meeting as well.
The Department holiday party is usually held in the lounge during the last week of fall semester classes. There is a fee, but the food is good. Most graduate students exchange white elephant Christmas gifts ($5 or less) at this time.
In the previous section, we already mentioned the Payday Friday Pizza get-togethers, pre-Colloquium Donuts and post-Colloquium Wine & Cheese, and the Journal and Unjournal Club meetings.