Answers to JM Crossword 54
Across
1.  Its shadow causes eclipses. (4)
    Answer: MOON
    Logic : Obvious.
3.  Turn a tuba about to lean on.(4)
    Answer: ABUT
    Logic : Anagram of TUBA. ABUT means lean on.
6.  It is worth having a donkey followed by an extra terrestrial. (5)
    Answer: ASSET
    Logic : ASSET means something worth having. A donkey is an ASS, followed by ET, an extra terrestrial, is ASSET. 
8.  Was it under a shadow on 22/07/09 ? (3) 
    Answer: SUN
    Logic : There was a total solar eclipse on 22/07/09 when the SUN was completely shadowed by the moon.
10. A question in a flask ? (3)
    Answer: ASK
    Logic : Contained in flASK, to ASK is to question.
12. The last broken den. (3)
    Answer: END
    Logic : Anagram of DEN, the END is the last.
14. Brightly following the night. (3)
    Answer: DAY
    Logic : Obvious.
16. The mistake in terror. (5)
    Answer: ERROR
    Logic : Contained in tERROR, an ERROR is a mistake.
17. Found in the oceans and in sal trees. (4)
    Answer: SALT
    Logic : Contained in SAL Trees, SALT is found in the oceans. 
18. Nips around to turn round and round. (4)
    Answer: SPIN
    Logic : Anagram of NIPS, SPIN means to turn round and round.
Down
1.  Decoded spam could show you the way. (4)
    Answer: MAPS
    Logic : Anagram of SPAM. MAPS could show you the way.
2.  Moan around near the Persian gulf. (4)
    Answer: OMAN
    Logic : Anagram of MOAN. OMAN is near the  Persian Gulf.
4.  The second letter in Greek and the on in Hindi. (4)
    Answer: BETA
    Logic : Obvious.
5.  Good wood obtained when the kettle in initially added to the tea ! (4)
    Answer: TEAK
    Logic : TEAK is good wood. Kettle initially is K, added to tea gives TEAK
7.  Rise around a roman fifty to get something referring to 8 ac. (5)
    Answer: SOLAR
    Logic : To rise is to SOAR, a roman fifty is L. SOLAR is something referring to the SUN. 
9.  A vase in a turn. (3)
    Answer: URN
    Logic : Contained in tURN, an URN is a vase.
11.  Seen at the beach it has a lot of 17 ac. (3)
    Answer: SEA
    Logic : Obvious.
12. Consumes by mixing up the east. (4)
    Answer: EATS
    Logic : Anagram of EAST. EATS means consumes.
13. Upsets the lead to make an agreement. (4)
    Answer: DEAL
    Logic : Anagram of LEAD. A DEAL is an agreement.
14. Given drop by drop in case of medical emergencies. (4)
    Answer: DRIP
    Logic : Obvious.
15. A story woven from it ? (4)
    Answer: YARN
    Logic : YARN is a story. It also is the thread from which cloth is woven.