Here is a list of things to consider on the Astronomical Aspects of your world

Galactic Location -
Where is it in the galaxy it resides in?
How big is the galaxy?
How intense is the light from the galaxy?
How much additional radioactivity is there?
What type of galaxy is it?

Celestial Mechanics - You have to understand your planet's solar system, its sun and moons and how they would appear to the inhabitants.

The Star -
How bright is it?
How large is it? Star size and brightness determine how long life can exist on planet.
How far away is it?
What color does it make the light on your world? A redder star would leave a pinkish cast to the world's colors and atmosphere.
How many planets orbit the star?
How many planets are orbiting in the life zone of the star?
Is it part of a multi-star system?
What is the age if the star?
What is the chemical composition?
What is the solar flare level?
What is the sunspot level?

The Planet -
How big is it? A bigger planet tends to have more gravity and makes your people shorter
Where does it sit in the solar system?
What’s the gravity like?
What are the materials that make it so?
What is the magnetic patterns like? A solid inner core is needed for a good earth like gravity and the magnetism needed for independently developed life.
Is it a cold planet, normal by earth standards of today, hot?
What is the tilt of the axis?
How intense are the seasons?
Are there rings? A planet with rings must be big enough (Neptune sized) or far enough away (Neptune again) making life unlikely.
What is the atmospheric composition?
For anything else see the “The Physical World” section.

The Moons -
Do you have moons?
How many are there?
How big are they?
How big do they look from the ground?
What color are they?
What is their appearance?
How far are they from the planet?
What is their chemical composition?
How strong is their electro-magnetic system?
What is the geological activity level?
Does it have an atmosphere?
Could it have life?
What kind of pull does it have on the tides?
Any unusual features?

For Geology of your planet, past and present, see the Physical Planet section.