[Plamadude30k]

Oh, we have a driveway. It’s quite narrow, but it’s long enough for three or four cars beyond mine (which I rarely take out), so you should be fine.

[Plamadude30k]

Wow, I completely forgot it was Wednesday. I suppose that even if I had remembered, I wouldn’t have been able to do anything this week (or the last few weeks, for that matter). The work hammer has come down, and unfortunately it doesn’t look to be letting up within the next few weeks.

[Plamadude30k]

Lights: The more the merrier.

Truth. When I’m doing photometry, I usually take a few hundred flats (or lights, I think the terms are interchangeable). I had a research colleague who would insist on taking well over a thousand for each night of observation, but she was a little crazy. There IS a point where taking more flats wastes more time than it’s worth, but if you’re willing to waste some time, it won’t hurt.

[Plamadude30k]

April looks pretty good right now, so I can’t see any reason why you couldn’t come stay. I live in the Manoa valley, basically right in the center of town, but back in the mountains from the city, so it’s a very quiet neighborhood. We’re a short walk from a bus stop that takes you downtown (and a little longer walk from the main university bus stop which operates later). I can give you an exact address in a PM if you like.

[Plamadude30k]

Can’t wait to see the results from this, especially since it the next thing on my “Big Ol’ List O’ Camera Stuff To Buy”

[Plamadude30k]

man if I could lug a 120 lb rig to Hawaii, I could nearly afford it right now!! But ain’t gonna happen!! (I want the f/2 rig; I’m certain; money better spent.)

Please continue your digression, I was just getting into it!…

Go for the f/2 rig. My air mattress will still be waiting when you save up enough again to get out here. That goes for all y’all out there, too. Just let me know well in advance if you want to come visit.

Okay, as for flats, darks, and biases, here’s the info:
Flats: Exposures of a ‘flat’ field with a uniform brightness across the field using exposure times similar to that of the data. One trick is to point the telescope at a flat, evenly illuminated wall or board close to the telescope (so that it’s out of focus). Another trick is to use the sky either just after sunset or just before sunrise when it’s uniform in brightness, but you can’t really see stars. Sometimes, using the telescope, you can still see stars, so to make a good flat, you might need to take a few images of several different locations (with different star patterns) and average them (or, really, do a median combine).

Darks: This is the most important calibration frame for DSLRs. As long as they aren’t cooled, the sensors see a lot of dark current. Basically what happens is that the temperature is high enough to ‘boil off’ some electrons in the sensor, which makes it look like you’ve detected photons when you haven’t. To correct for this, take images at approximately the same exposure time as your data with the lens cap on and do a median combine (for DSLR purposes, averaging is just fine-on astronomical sensors, median combining is to get rid of cosmic rays).

Biases: This one probably isn’t useful for DSLR astrophotography-other noise sources (see above) way overpower this. Essentially, you use biases to calibrate out the base level of electron charge in each pixel. This only matters if you’re doing extreme precision or extremely low flux objects. Bias frames are taken buy keeping the lens cap on and taking photos with the minimum possible shutter speed.

[Plamadude30k]

ohshit…don’t get me going… a parsec is likely the most obtuse measurement ever conceived… it’s practically arcane, but roughly equal to about 3 1/4 light years. The nearest star to Sol is about 1 1/4 parsec. I’ll leave it up to y’all to gather scale on that. Do a wiki to get the definition, it’s an odd standard for measurement, but a standard it is nonetheless.

If you think that’s odd, try doing astronomy in cgs (centimeters/grams/seconds as opposed to MKS, meters, kilograms, seconds). Insanity. Also the standard units of astronomy to this day for stupid historical reasons-we still use ergs. Even wolfram alpha thinks ergs are a deprecated unit.

Parsecs are actually incredibly useful for astronomers, though. The definition of a parsec is the distance to an object that shows the parallax angle of 1 arcsecond given a baseline of 1AU.

Okay, maybe that didn’t help. Uh, well, it’s defined by geometry using the earth’s orbit and the distance to an object.

Hmm. Okay, yeah, it is a bit arcane. Sorry. I should have just said “HII regions can be really frakkin’ big.” and left it there. Of course, that’s ignoring the Ultra-compact HII regions, which are sub-lightyear sized, and all the intermediate variation.

But I digress.

Rav, how did you make your flat frames? Did you take any bias frames (meaning 0 second exposures with the lens cap on)? And how’d you make the Bahtinov mask? I’d like to try one myself.

[Plamadude30k]

Red is emission, hydrogen gas excited by the ultraviolet from “nearby” stars…

Red is, in fact, H-alpha emission, which is the 3-2 orbital transition which produces light at ~656 nanometers. Orion is, in fact, an HII region, where all of the hydrogen is ionized by UV continuum photons. The size of these regions can get up to about 70 parsecs across! (sorry for the rambling, we just did HII regions in my ISM course. I never thought I’d know so much about dust and gas.)

Anyway, amazing photo, Rav. This only galvanizes me further to get a tracking mount.

[Plamadude30k]

As long as we’re talking about scopes, I was wondering if anybody had experience with a lightbridge? I’d love to get a 10″ or a 12″ (or, really, the 16″, but I am still a poor grad student), and it’d be nice to hear reviews from people who I know I can trust (that’s y’all here).

Oh, and conga-rats, rav. I expect great things…well, okay, even greater things, I guess 🙂

[Plamadude30k]

Well, this thread got me to tallying up what gear is gonna cost me to assemble a tracking rig. Looks like I’ll be blowing part of my income tax refund on a geared head, a ball head, an astrotrac and the optional polar alignment scope (is this thing really optional?). Considering the camera, lens, tracker and ball head weigh in at about 10 lbs total, that kinda drove the price of the geared head up a bit… total take wound up being about $1300…

Yuss! The astrotrac and a geared head has long been on my list of things to get. Maybe by the summer…

[Plamadude30k]

Man, this sounds it’s shaping up to be just my kind of shindig. I’ll have to figure out if I can get back to the mainland for it.

[Plamadude30k]

Coming from NM, I can vouch for the dark skies. When I was a kid, I used to be able to go out to my backyard at a certain time of year and without looking, point directly at the andromeda galaxy because I had seen it so many times. That was until the biggest walmart in the entire city was put in three blocks away. Now, if I’m at my parent’s house, I have to drive about 15 minutes north to get comparable skies to what I used to have.

Darkest skies, though? Eastern Sierra, west of Lone Pine at about 10000′. The milky way was casting shadows. I could see the gegenschein-I don’t even know anybody else who has seen that. Mauna Kea summit with no moon rivals that-the problem there is that you’re so oxygen deprived, your eyes are less sensitive, and the volcano throws up a surprising amount of light pollution in one particular direction.

A very close second is back in the eastern sierra west of bishop near Lake Sabrina. Bishop is bigger, so you can certainly see the light dome, but there’s a little dirt road off the main pavement called “Starlight Drive” which is a great place to do some stargazing.

[Plamadude30k]

Exactly 😀 It was either there or VLA, and I figured VLA would have better skies than the Puerto Rican sauna.

VLA is actually way more likely-it’s only a couple hour drive from where I grew up, and where my parents’ house is.

[Plamadude30k]

Arecibo? Some weird stuff would have to go down for me to go there. I’m not even a radio astronomer. I’m going to do my damndest to get ahold of something in the 10-16 inch range for that day. We’ll see how it goes.

[Plamadude30k]

Yep, I’m starting to make plans for the transit of Venus, since the WHOLE THING will be visible from first to last contact from here!

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