So in the lead up to creating my own campaign, i decided to create my own magic school, called the School of  Cosmology. So far I have one cantrip and a 1st level spell:

Cantrip- 

Piercing Star

1 action, Duration: Instantaneous, Range: 60ft, School: Cosmology or Evocation (for other settings), Components: V,S

You raise your hand and a blinding beam of pure starlight lances from your palm towards a creature in range. Make a ranged spell attack. On a hit, the target takes 1d6 radiant damage and the starlight explodes, causing them to emit bright light for 5ft, and giving them disadvantage on their next attack roll against something within 5ft of them.

At 5th level, the damage increases to 2d6. At 11th level, the range of the light and disadvantage increases to 10ft. At 17th level, the damage increases to 3d6. 

Spell-

Cosmic Presence 

C. Time: 1 minute, Duration: 10 minutes, Range: Self, School: Cosmology or Divination (in other settings), Components: V,S,M (a silver amulet shaped like a six-pointed star, worth 20gp)

You focus on the amulet and project your consciousness to the stars, causing an ethereal version of yourself to appear out of you, a grey incorporeal version of you dotted with small stars. For the duration, you may see and hear through the senses of this form, and move as if it were your own body, though it has none of your abilities save special vision like darkvision and it cannot move further than 1 mile from your body. You are blind and deaf whilst seeing and hearing through it. It has a fly speed of 20ft, and is solid despite its appearance. If a creature tries to attack it, the form is destroyed. Otherwise it lasts for the duration, until your real body dies or falls unconscious or until it does an action or an action is done to it that would cause it damage. When the duration ends, this form disappears and you return to your own body. You may end the spell as a bonus action. 

Other than those, I have no real ideas. Any inspiration would be appreciated.

Edit: Thanks to Astromancer for making me realise I need to clarify this, but I'd rather spells focused around more modern understandings of space, such as black holes and gamma rays, as well as ones centering around the Astral Plane and just generally the heat and power of stars.

Consider what version of the cosmos you are exploring with the school. Are you thinking about astrology and the relationship between the celestial sphere and the celestial planes? Are you taking inspiration from the old Ptolemaic ideas of the sky, in which the Earth sat at the center of a great orrery encased in crystal spheres and submerged the flammable phlogiston?  Or are you drawing from our current understanding of space filled with black holes, neutron stars, massive spheres of fire and plasma, and on occasion, habitable Earth-like planets?

If you’re leaning more towards an astrological point of view, consider radiance, divination, constellations, the sun, as well as the planes of existence, in particular the astral and upper planes.

If you’re pulling from the Ptolemaic model, like D&D does (much to my disappointment), you can create spells that connect with crystal spheres, the flammable phlogiston and the wild shapes that planets take.

If you‘re like me and like your D&D to involve up-to-date understandings of the cosmos, than look for inspiration in black holes, neutron stars, gamma ray bursts, and other space phenomena.

here is a spell i made spell

Cataclysm - 9th-level Cosmology. Casting time: 7 days. Duration: until dispelled by a Wish spell or another Cataclysm.

You remake the shape of the world as you see fit: change a flat world to round, flood dry land, reverse gravity, alter the geometry of the planes; the sky is not the limit. All creatures, objects, and locations remain in the world, but suffer the natural consequences of the sudden change.

OR

Change a single rule of the game.

Probably also some spells to do with the astral plane.