Hi there! I see that your Star & Planet Finder app on your iPhone with iOS 18.6 keeps crashing and just won't open. Let's work through a few steps to get it running smoothly for you.

First, just to make sure we're not repeating steps, have you already tried uninstalling and reinstalling the app? Also, is your iPhone connected to the internet when you try opening the app? Sometimes the app requires an active internet connection to function properly.

If you haven't tried these, here’s what I suggest:

1. Check Internet Connection
Make sure your phone is connected to Wi-Fi or cellular data before launching the app.

2. Force Quit and Restart the App
- Swipe up from the bottom of your screen and pause slightly in the middle to bring up the app switcher.
- Find Star & Planet Finder and swipe it up off the screen to close it.
- Then try reopening the app.

3. Restart Your iPhone
Restarting your device can clear temporary glitches:
- Hold the volume up (or down) and side button until the power off slider appears.
- Slide to power off, wait 30 seconds, then hold the side button to turn it back on.

4. Update the App & iOS
- Open the App Store > tap your profile icon > scroll to updates > check if Star & Planet Finder has an update and install if yes.
- Also, check under Settings > General > Software Update to ensure your iOS is the latest version. iOS 18.6 is recent, but an update may help.

If it still crashes:

5. Clear App Data (if possible)
iOS apps don’t have many user-accessible cache clearing options, but uninstalling the app completely removes app data. After uninstalling, restart your iPhone before reinstalling.

6. Check for App Permissions
Go to Settings > Star & Planet Finder and ensure it has necessary permissions like location and network access.

7. Look for Known Issues
Some users report the app crashes when tapping on any planet or specific functions. If that’s your case, it might be a bug in the app needing an update from developers. You can visit the App Store reviews or the developer’s support page for updates or report your crash.

If after all these your app still crashes immediately on launch, it could be a bug or compatibility issue with iOS 18.6, and I would recommend reporting this to the developer via the App Store’s support link for Star & Planet Finder.

Please let me know what steps you have tried so far, and I’m here to guide you further! Are you satisfied with this approach so far?