Related Clues:

• Concern
• Count
• Saturn, for one
• Stuff
• Astronomer's sighting
• Physics topic
• 5-Down, for example
• 'What's the ___?'
• Affair
• See 19-Across
• See 59-Across
• Sun circler
• Vulcan, for one
• Jupiter, e.g.
• Saturn or Mercury