I observe variable stars, I'm a member of the AAVSO (American Association of Variable Star Observers; aavso.org). I do not want to talk about observing as such, the technique or suchlike. But all my stars are having some in common. They are old, cool (wordplay!), red giants and supergiants, some will become supernovae. But the most important is, they have long or very long periods. Long means mostly over 400 days, up to over 700 days. Therefore, you need at least one year, sometimes two years, to observe a single cycle – I like this.
Another aspect is, that the cycles are not always the same – in fact, not one is like the other! You never can say what will happen, especially long-term. The variation of brightness can be sometimes very significant, sometimes small. Some stars have alter their light change totally – sometimes this is bad. One star became significantly fainter, V1666 Cyg. Others were easy to observe, but no longer (U Lac or LW Cyg). One showed a so-called dust event over the last decade, became fainter, now brighter again. I could observe this star fortunately all the time – CT Lac.
Science, yes, the question of the origin of the universe for example. Or quantum physics, but science can also mean very practical doing. I've a telescope, but also a microscope. Nothing has changed the history of the humans more than scientific insights, I will write about this.