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How important can the date be?


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If you've read some of my previous posts, you'll know that I don't like to spend more than necessary on my equipment - mainly because that way I don't lose too much if I make a bad buy.  So when I came in to some money recently, I decided that I couldn't pass up on the opportunity to buy a NexStar 90GT for next to nothing; especially when Celestron had confirmed to me that my 130 Astromaster would be compatible with the mount.  I'd read some forums that mentioned the mount would soon run out of power if you tried to run it off AA batteries, so I also bought myself a battery pack.

When the new gear arrived, I was blessed with an evening of relatively clear skies and set up the equipment.  Rather than use the 130, I decided to give the 90 Reflector a go.  So there I was, sitting in the garden waiting for the skies to darken and 3 stars to pop out so I could align the mount.  I'd looked up my latitude and longitude on my iPhone and entered the date and time in the hand control too, so was all set to go.  I had a mug of cocoa (having been advised before that drinking cocoa has a lesser effect on your ability to focus than my previous warming drink of a large brandy) and my trusty towel for dew protection/removal and used the waiting time to have a good look at the very bright moon.  So what could possibly go wrong?

The stars started to appear, so I began aligning the mount.  I slewed the scope towards my first star, hit it dead centre and moved on to star number 2.  Everything seemed to be going well as I ticked off my second star and set off in search for star 3.  Everything was going swimmingly as I centred in on my 3rd star and I told the scope to confirm the alignment.  That's where everything went wrong; the hand control came up with the result of "Alignment failed".  My language deteriorated somewhat as I began again.

During the second attempt at alignment, I kicked the tripod by accident as I was slewing towards the third star.  The phrase "Oh what a silly thing to do" came to mind, but the actual utterance was somewhat more colourful.  I could hear the brandy calling, so took a sip of my cocoa and began once more.

The third alignment check failed to confirm success, so I reduced the requirement to 2 stars.  I picked two new stars; one east and one west, centred the scope and............. alignment failed.  I reached for the cocoa again.

There was one final option: get the handset to select a single star and centre it in the scope.  So I moved the scope around, centred on the required star and...................... Success!!!!!  The handset informed me it was now aligned!!  Hooray!!!  Time to celebrate with some more cocoa!!!!

So now I was in a position where I could move the scope around the sky and look at whatever I wanted.  I decided to start by getting the scope to slew itself back round to the moon, just so I could see how accurate the alignment was; would it centre on the middle of the moon or on the middle of the visible portion? I wondered to myself as the scope turned across the sky.  The answer: neither - it missed by approximately 3,500 kilometres - the diameter of the moon.  I'd now run out of cocoa.

So I went back to the beginning.  What had I done wrong?  I followed each of the steps through. 

Lat and Long? Fine. 

Time agreed with my iPhone. 

Date?  Errr...... Monday. 

Correct Date? Errr... Wednesday.

So I put the correct date in, aligned using the single star method and then tried to find the moon again.  There it was in the centre of the scope, but looking a little bit fuzzy.  I moved around to the other end of the scope, kicking the tripod once again in passing, only to find the lens covered with dew.  At this point, I felt there was only one course of action that would guarantee success; I packed up, went inside and poured myself a brandy.

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I've had so many nights like that. Sometimes it's a 'mare, sometimes it just works. I always think you learn most from mistakes. If this is the case, I must have learned a lot by now :)

My favourite was checking focus one last time before embarking on a set of very long exposures that took a whole night. Obviously I had left the focus mask on.

The 90 is a refractor so will suffer from dew more than the primary on a closed tube reflector tends to. A camping mat DIY dew shield might help if, like me, you're into the budget thing; mine works a treat and only cost a couple of quid. I'm always happiest when something involves gaffer tape.

With a refractor (back when I had some money!) I never managed to keep dew at bay successfully without a dew strip and a dew shield. If you already have the battery pack a 12v camping hair dryer might also help a bit.

Oh, and one more thing I just thought of; if you are on concrete and can drill 3 shallow holes for the tripod feet it will be surprisingly resistant to the odd nudge. Bit of weight on the mount or on each leg also helps a lot.

cheers mate

Chris

Edited by m37
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I know what you mean about "checking the focus" - I put my 130 Astromaster Newtonian scope on the NexStar mount to get some pictures of the super moon.  I made sure everything was in focus before grabbing two sets of 20 shots to stack later.  I'd forgotten to put my glasses back on before refocussing, so although the viewfinder was in perfect focus for my dodgy eyesight the pictures were useless!!  Of course, I didn't discover this until the following morning.  Perhaps I should be looking to change back to contact lenses!!!

I like the idea of the camping mat - I've loaned the scope to my father in law (on my EQ mount - the Astromaster and NexStar GT seem to be completely interchangeable which is great) so when I get it back I'll give that a go.  I find the towel over the mirror end on the Newtonian works well enough, but a camping mat would probably be better.  Rather than gaffer tape, our local 99p and pound stores stock reels of Velcro designed to be used to attach plant stems to garden poles.  I measure it to the circumference of whatever I'm wrapping it round, add a couple of inches and cut.  It sticks to itself so there's no mess and is completely reusable.  So far, it's been used to hold my towel in place, strap a camera bag with my eyepieces in to a leg of my tripod, as a tie to hold my tripod legs together when packed away and the like.  I've also used the Poundland car brake light repair tape to make my 99p strap on head lamp red!!

As for drilling some holes, my wife would kill me!  I'm currently using the patio but think I'll move up on to the raised grass area simply because it gives me a wider view of the sky being further away from the house and I can stake the tripod legs in place - it's either that or I'll turn the garage roof in to a permanent observatory!!

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The answer to your initial question is probably "very important". If you enter the wrong date the mount will point to the date entered rather than the date at use. The objects in the sky are at a different position in the sky on alternative nights at the SAME time of night. Try this one on Stellarium,  :smiley:

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Live and learn  :p

As for setting up on a grassy area you might want to think about putting something solid under the tripod legs to prevent them sinking. I use some old tiles I had left over from my kitchen refit.

I'm going to see what I think of the location, then I'm thinking that some ground spikes for washing lines angled to allow the tripod to be slid in may be the way to go - the floor tiles will be needed for the calor gas heater, camping table and deckchair; who says you can't be comfortable whilst doing a 20 minute image!! 

Additionally, I've bought myself some ovaltine, mint chocolate and white chocolate drinks.  I'm not sure they will go with brandy, so may have to switch to whiskey going forward.

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