An adult who loves astronomy might like a related gift for the 2010 Christmas holiday. There are many great presents that are appropriate for a variety of budgets.
Trip to the Kennedy Space Center
An adult who loves astronomy might like a trip to the Kennedy Space Center in Florida. They have a facility where you can learn about the space program and see actual items that were taken on space missions. You may even be able to meet an astronaut. They have many exhibits, and you might be able to spend several days at this expansive facility. You can give them tickets to such a place or spring for an entire vacation.
There are many other vacations on which you can send an adult who loves astronomy. You can send them to the Smithsonian in Virginia or Washington D.C. (they have two campuses that explore the space sciences). There is no admission cost to these, however there are other costs that you can pay for like parking, transportation, etc.
If you want to send them on a particularly amazing experience, then you can send them to Huntsville, Alabama, to do the adult version of Spacecamp. They have different programs where they can get a feel for what it is like to be a true astronaut. These are not inexpensive, but they can be the experience of a lifetime for someone who loves astronomy.
Book on astronomy
You will find many different books that explore astronomy. You can get a coffee table book that showcases brilliant pictures from the Hubble. You can also get them a non-fiction book that explores astronomy in general or particular celestial bodies such as stars. You can get them a fictional book that takes place amongst the stars.
They make many beautiful calendars that show pictures of the stars, planets and other astronomical objects. This can be a practical, beautiful, long-lasting and inexpensive gift.
There are many other astronomy themed presents that you can get for an adult that likes the subject. They might like a magazine related to it. You can get them a non-fiction DVD of one of the IMAX movies or a fictional DVD of a science fiction powerhouse like Star Trek. They might even love a telescope. You can find these for under $100 or spend well into the thousands depending on the features and power. Combine your budget with what you think they would like to come up with the perfect gift.