Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

“Why’s it upside-down, Mister?”


Recommended Posts

“Why’s it upside-down, Mister?” is the age-old question asked when someone looks through an astronomical telescope for the first time, normally when viewing the Moon.  The usual answer was that there is no up or down in astronomy and to get the image the right-way-up would involve using more lenses which would reduce the light gathering power of the scope.  It therefore became the convention to publish all astro photos as inverted images as a result, and lunar maps were always orientated with south at the top.  Checking through my small collection of astronomy books, I find this was the case until a few years ago.

I assume the reason is that as most modern astro set-ups have such complicated light paths, there is no definitively correct approach.  So, does it really matter, or does it depend on what one is used to? To an old timer like me, a whole-disk image of the moon looks strange with the crinkly bits at the bottom, and I also find that images of familiar deep sky objects like the Orion nebular look odd when inverted.  This issue was brought home to me when I tried some simple afocal lunar imaging through my recently completed 8 inch Dobsonian, see here:

http://stargazerslounge.com/topic/255887-8-inch-dob-finished-at-last/

When I downloaded the photos to the PC, I rotated & straightened them to get south at the top of the frame, then went online to make comparisons with images displayed on SGLs Imaging forums.  I could find none with south at the top which got me mentally asking the posters, “Why’s it upside-down, Mister?”

post-680-0-39060500-1448635430_thumb.jpg
 

Link to post
Share on other sites

And it can be a pain when using a star-diagonal and you have to remember East is West...

...and West is East.

** EDIT **

I forgot to mention that this applies refractor and catadioptric telescopes* with the star-diagonal in place and North & South are at their respective positions.

* ie Maksutov's (Mak's) & Schmitt-Cassegrain (SCT's)

Link to post
Share on other sites

Since I started this thread, I have found an interesting passage in “Patrick Moore on the Moon” written in 2001, in which Sir Patrick mentions the debate at the General Assembly of the International Astronomical Union when they attempted to reach a consensus when referring to the orientation of the Moon.  Being a traditionalist, Sir Patrick argued for the well-established classical view with south at the top, east on the left & west on the right.  The vote subsequently went against him and in favour of the naked-eye view with north at the top, but with west on the left and east on the right.  So, whereas Mare Crisium was formally considered to be on the Moon’s west limb, it has now been moved to the east limb.   No date was given for this decision but as Sir Patrick implied that the change was in deference to space-flight engineers, I assume it was in the nineteen-sixties.  Although he stated that he would accept the ruling, he can still be seen on the book’s cover, defiantly cycling across the Lunar face with south at the top!

post-680-0-83973400-1448903876.jpg

Link to post
Share on other sites

My deep sky images are (unless I goof things up!) presented unflipped and 'North is up.' At least they are meant to be.

In the digital imaging world the 180 deg. rotation and freedom from 'flip' (mirror imaging) comes at zero cost to resolution so it seems to me to be logical to respect it.

Oh, and the astro image critic I most respect, no longer seen on SGL, has a distinct preference for 'N is up' and I like to get in his good books from the off by sticking to this!  :grin:  :grin:

Olly

Link to post
Share on other sites

The "thought experiment" required to guess the (video) image orientation

usually defeats me! But there's nothing like experiment... :p

I now record the orientation in a quick drawing!  

I do like to compare with stock images, so strive to align with ONE of the

cardinal axes. Nothing worse than an image that's a "few deg" off! :angry5: :D

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.