Earth and the Universe

Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

       1        2         
3              4          
                    
      5                
                6      
   7          8      9       
                    
     10            11       
                    
          12            
                    
                    
      13     14   15            
                    
        16              
 17                     
      18