Each day at 10:45 it is typical to stop by the Kaiser Lounge and grab a tasty beverage of your choosing. Tea and coffee are provided free of charge by the observatory. This is a very casual occasion and there is no pressure to come at this time every morning, but it is the most active time of the day at the Kaiser Lounge and a great way to network or just catch up with friends.
If it happens to be someone's birthday at the observatory, he or she might follow the Dutch tradition of bringing a cake and sharing it with everyone. This is typically done during morning coffee, so watch for announcements in your Sterrewacht email! It is not a requirement to bring something on your birthday, but it's a nice way to introduce yourself to those who have not yet met you. Besides, who doesn't want sweets with their morning tea or coffee?
The borrel is another fantastic Dutch tradition that occurs every Friday at 17:00 in the Kaiser Lounge. It's a pleasant way to kick off your weekend with a cold beer or nice glass of wine and chat with your colleagues. You can network, socialize, snack, drink, and be merry while getting to know your fellow Sterrewachters. Beer and wine come at a small price: usually 0.70 cents to 2 euros. Borrel snacks such as nuts, olives, and cheese are provided for free.
A unique twist on this Friday afternoon routine is the Cultural Borrel, which happens on occasion in place of the regular borrel. The borrel organizers will as for volunteers to cook typical dishes from their home country or region and bring it to the borrel to share with everyone. Drinks remain priced, but the food is still free. It doesn't last long, so don't show up late to a Cultural Borrel.
De Leidsche Flesch (website only in Dutch), the student association for mathematics, computer science, physics, and astronomy, hosts drinks every Thursday evening at the Foobar on the ground floor of the Snellius building. Drinks are cheap and there is a nice social atmosphere to help de-stress after a hard day of work.
Sinterklaas is a holiday that can't be missed. It is celebrated in The Netherlands on December 5 & 6 of each year and includes a bishop who hails from Spain and his quirky helper, the Zwarte Piet. These characters all make a special appearance at the Sterrewacht during their visit to Leiden and come bearing gifts for a small selection of the PhDs, Postdocs, and Faculty. If you happen to be in your office just before the arrival of “De Sint” then you might get a visit from one of his Zwarte Piet helpers, who may or may not shower you with kruidnoten, pepernoten, and other traditional Dutch sweets common around Sinterklaas.
This event usually takes place in the canteen on the floor of the Oort building. Sweets are provided, along with lyrics to Dutch Sinterklaas songs, and a guaranteed laugh at some of the great gifts that Sinterklaas brings to the Sterrewacht. See here for old photos of a previous Sinterklaas visit from 2005.
The observatory hosts an annual Christmas lunch around the middle of December. It is commonly located at the second floor of the Huygens building, with one large lecture room hosting the food and another hosting the dining area. The event is an excellent fusion of typical Christmas dishes from all over the world and it nicely reflects the highly international assortment of astronomers and students at the Sterrewacht in the most delicious of ways. You can find everything from freshly fried herring (that will leave the stairway smelling for days) to hearty winter soups to light salads to towering baked goods. It is the culinary highlight of the year and should not be missed.
As a potluck lunch, each person that attends the lunch is highly encouraged to contribute a dish of their own. When the date approaches, a sign up sheet will appear on the door in the Kaiser Lounge. There you can register for the lunch by putting down your name and the dish that you plan to bring. It can be anything, sweet or savory, and doesn't necessarily have to be Christmas-related. See here for photos from the 2009 Kerstlunch.
At the start of summer, the Sterrewacht organizes a (free!) summer barbeque for everyone in the department. This BBQ involves lots of food, drinks, activities for kids. The food is provided in a grill-your-own environment with a large variety of meat and vegetarian options to bring to one of several grills set up outside of the main entrance to the Oort building. Previous years have included an inflatable bouncing castle, which is just as much fun for the MSc's, PhD's, and Postdocs as it is for the children.
In addition to the regular events listed above, the observatory also has a Social Committee (SOCCOM) that organizes other social events. The SOCCOM website also hosts some useful information, though it may be out of date.