Major in astronomy?
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">major in astronomy?</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ursa that I've seen before include "(In the sky) Major or Minor" , "(& 19 across) Plough constellation" , "- Major, - Minor, prominent constellations" , "'Major and Minor, constellations (4)'" , "stars" .)