Possible Clues:

• Unit of astronomical distance - scrape (anag)
• Unit that's larger than 19 trillion miles
• Describe word grammatically concerning astronomical distance
• Measure of distance in space; spacer (anag.)
• Long way from silly capers
• Paces rapidly round stores a fair distance
• Unit for measurement of distances of stars
• Explain structure of carbon at vast length
• Break down and analyse about three and a quarter twenty sevens
• Short paragraph on short time for astronomical unit