#92-Aperture Fever

It's Spring, and many of you will be dusting off the old telescope and getting it ready for the warmer nights that will soon be upon us.  A few of you might even have brand new scopes ready to receive first light.  And some of you may be thinking it's time to upgrade to a bigger scope.  The quest for more aperture is as old as astronomy itself, and when I think of the 100" and 200" telescopes that dominated my fixation with large telescope as a teen, and now realize that those instruments just aren't really so big after all, I wonder what my next step will be in telescope aperture.  Mapman began with a toy 3" reflector, quickly upgrading to the Cadillac of its day (in more ways than one), the Tasco Lunagrosso 4 1/2" reflector.  Who would ever need more aperture than that?  That was 1971, and that scope lasted me till 1978.  Along came the Edmund 8" reflector.  I was in aperture heaven!  I could see farther and fainter than ever before.  Who would ever need more aperture than that?  Not me!  That scope lasted me until 2012, when along came my Orion 12" Dobsonian reflector.  I am beyond pleased with it, and have been successfully tackling the northern NGC list.  Who could possibly need more aperture than that for amateur viewing?

Readers of this blog will remember that my most recent telescope, purchased last autumn, was the smallest one I have ever owned.  2" Space Eye cannot be considered as part of my desire for more aperture.  Why, then, did I purchase it?  I am still quite delighted with this instrument, and have been enjoying good views of Jupiter and its moons this Spring, along with outstanding lunar work.  It has brought me back to my earlier days of astronomy, when finding anything resembling a Messier object was a night time adventure of the first rank.  Last night (April 12th) I located M 44 (The Beehive Cluster) with Space Eye, despite a 5.5 day moon nearby in the sky.  What a kick!

Someday, when I have a place where I don't have to transport a scope 45 minutes from my home and back each time I want a dark sky, I would certainly consider upgrading to an 18".  I know I would never want a bigger scope than that (ha ha)!

Okay, enough about me.  Let's talk about two famous astronomers and their aperture fevers.  William Herschel, a German musician who became an astronomy fanatic, first built himself a 6" reflector.  His metal alloy mirror, which he designed and improved over previous ones in existence, had the ability to reflect about 60% of the light it received.  That's about equal to a good 4" mirror today.  Next he built a 9" mirror, which got him up to about a 6" scope today.  However, that scope was ten feet long (three meters), since curving the mirror was not possible in those days to the extent it is today (he did not use a secondary mirror, either, but had to look down into the tube to observe).  So his scope was something like an f 13 reflector!  Next came his most famous scope, his 18" mirror.  However, it was twenty feet long.  It is similar to a good quality 12" mirror of today.

Herschel's famous 40 foot reflector, with 36" mirror
https://upload.wikimedia.org/wikipedia/commons/6/62/Herschel_40_foot.jpg

Was he satisfied with that size?  Of course not!  Finally came his 36" mirror (photo, above), with forty feet of tubing!  Though valuable for observing dim objects, preparing it for a night of observing was so cumbersome that it was used only seldom.  Herschel mostly used his 18" scope for his deep sky work.  He built his scopes between 1781 and 1789.

We now jump to the middle of the 1800s, when Lord Rosse of Ireland was struck with his own version of aperture fever.  Herschel did not leave any notes behind about his mirror making process, so Lord Rosse had to start from scratch.  He made a 15" reflector, a 24" reflector, and then a 36" version!  These scopes took him seventeen years to build.  However, barely was the 36" mirror set into a Newtonian mount then Lord Rosse decided he wanted to build the world's largest telescope.  Imagine trying to do that today?  It wasn't much easier back then, either.  He began work on a 72" mirror, which took him five tries before he finally got one that would work.  Then it took three years to build the mount.  To see through the scope he had to sit on a chair fifty feet in the air.  Despite all his hard work, the scope was rarely used.  For one thing, it could barely move side to side, though up and down was not a problem.  Thus he could not see very far in right ascension, but had to wait for objects to pass in front of him.  The other problem was the damp, cloudy weather in Ireland, and terrible distortion caused by the atmospheric changes.  The mirror never had time to acclimatize properly before the next weather front moved in.  One good thing came out of this disaster; from then on sites for large telescopes were carefully chosen with the local climate in mind.  This telescope has been restored recently and can be visited at its original location in Ireland!

Lord Rosse's 72" reflector, nicknamed the "Leviathon."

http://amazingspace.org/resources/explorations/groundup/lesson/scopes/rosse/scope.php

Hopefully your aperture fever, when it strikes, will not be as extreme as either of these two gentlemen.  However, if it is, kindly keep us informed about your progress.

Clear skies.  
Mapman Mike.