Some of this bashing out will appear as a series of statements, some as actual gags. Whether they're funny or not doesn't matter. You have to produce many of the bad to create one of the good. Please bear with me..
Star of Bethlehem
Sirius (a very bright star)
1. 2000 years ago three kings followed a star. Was one of them a tsargazer from Russia? And if so, was he the real tsar of Bethlehem?
2. In Hollywood a new film is being made about the Nativity, staring Zsa Zsa Gabor as Mary and Stewie from Family Guy as Jesus.
3. If a king rules a kingdom, surely a tsar rules a tsardom... and a boar rules a boredom.
4. Zoodiac: a whole load of animals who live in the sky.
5. John McEnroe disagreeing with Sir Patrick Moore about astronomy: "You cannot be Sirius!"
Also, a quick glance at Guide 520 n. leads me to 'pole star', which has good potential for tsar / star comedy.
Let's consider the latter, 'pole star'. Double meaning: someone
Famous Poles: I can only think of one: Pope John Paul the second.
6. As a young man he had unusually high ambitions. He wanted to be king of Russia but had to settle for Pope rather than being the first Pole Tsar.
All being well you're stating to see what sorts of thought processes which go on when conceiving and crafting gags.
Best regards, Marc