You get up EVERY MORNING knowing that for the next 8 - 10 hours you get to think about a subject you love, and you get to have the opportunities ot make wonderful discoveries if you are 'good' at what you do. No other physical science has the holding wonder that astronomy does, so you are caught up in a tidal wave of excitement about the wonders of the universe and what you can learn about it each and every day. Sure, this sometimes gets lost in the day to day details of 'crunching data', but it is a small price to pay to pay your dues to one of the greatest exploration opportunities humans have ever known. Even I have my off days, weeks and months. But when I consider how fortunate it is that I have just the right skills to make my own contributions to this exploration, I remain thrilled.
There is the knowledge that, once your research on a particular topic gets published in the technical journals, it will be there as a resource for someone 100, 200 or 300 years in the future! Some papers hardly get more citations than the ones you yourself provide; others get heavily cited by other researchers in the ten years after its publication, while still others are 'sleepers' playing to an even more remote audience in the future. You never really know what will happen to your papers. You watch your papers like stocks on the stock market, and celebrate when they 'take off'.