Wednesday, October 15, 2008

observational astronomy: challenges and puzzles

a nebulous nursery lives about 7,000 light-years away from us and is known as the carina nebula.

the carina nebula encompasses such interstellar wonders as the powerful star, eta carinae, and the star-forming region, NGC 3324! the above 50 light year, wide-angle image comes from the hubble heritage project, and reminds me of one of my favorite aspects of observational astronomy; trying to find the particular patterns inside an image that you want to point your telescope to.

for instance, imagine you want to further explore the properties of a dust pillar in the carina nebula, by collecting special observations that no one has previously created. all you have are the coordinates of the object and the Hubble reference image that comes from the larger image above:

you have successfully written a proposal to do the research, you were granted the observing time on the telescope, and now you are sitting inside the telescope dome ready to commence observations. having completed all your calibration tests, you program the coordinates of the pillar into the computer, move the telescope, command the technology to take a data image, and a short bit later, a raw image pops up on your computer screen:

(please note: the raw image directly from the telescope would look black and white, have much lower resolution, and probably not show much more than the stellar points of light**, but stick with me during this simple demonstrative scenario... i simply captured these shots while interactively exploring a wide-field view of carina)

from your telescope snapshot, you expect to see something vaguely like the above hubble image you prepared before arriving at the observatory, but clearly you are looking at something else! oh no... it appears that the pointing of the telescope is not correct by some unknown amount and your job is to sort it all out: find your object in the sky, correct the telescope's pointing, and get on with the collecting data before you've wasted too much time in the night.

so you search around the original wide-field image for hints of the structure you see in the telescope image, keeping in mind that you may be comparing two images with different orientations, rotations, flips, and/or flops (the challenge for anyone interested is to find the two cut outs above in the first image of the entire carina nebula). finally, you think you've identified what you are seeing thru the telescope, so you estimate which direction you must digitally nudge the telescope in order to move it just the right way to exactly image the dust pillar!

most likely you iterate this process until you have found your object!! once the telescope is properly aligned, you excitedly start exposing your image, and sit back hoping nothing goes wrong with the whole setup while you wait to see your data!

each telescope seems to have different pointing accuracies, with each individual telescope performing less precisely when tipped over to more extreme angles. people who own their own smaller telescopes are probably familiar with these issues. the biggest (most expensive) telescopes in the world have teams of astronomers and technicians around, specially trained to understand their particular quirks and tendencies, which makes observing during a night much more time efficient. smaller telescopes (2-4-meter class) generally allow training students and regular astronomers to use them - left to individually discover the quirks and fix any problems that should occur during the night! personally, i find the latter opportunity to be quite fun, most of the time. sometimes its incredibly frustrating if something serious goes wrong, or you cant solve an issue and have to wait for the regular staff to fix the problem during the day!

** the quick acquisition images used to isolate a target in the telescope field of view are generally not able to detect any kind of nebulosity. usually i locate my target galaxies using patterns found in the the bright stellar points of light in the image... but i thought the nebular features were more visually stimulating for this discussion ;)


Just Holly said...

amazing images!

Eva said...

You made me remember a looong night at the 30-inch telescope with Amy and Remco. We spent hours trying to figure out our pointing before we realized that the telescope controller was exposing with the wrong filter. I felt particularly stupid at that moment.

On a side note, I just got a beautiful poster of the Carina nebula released image on the mail. It's amazing!.

Florian said...

Hey! It seems that Mike is working ;)

Nice pictures!

astropixie said...

eva reminds us of the myriad of unpredictable problems that could occur when operating these beastly telescopes.... potentially resulting from both technical issues and operator errors!! haha!

hello florian - maybe i made mike move his beer before i took the picture ;)

florian said...

"hello florian - maybe i made mike move his beer before i took the picture ;)"

That sounds more like him! Apropos beer drinking austrians: give my best regards to Ruth ;)