I've returned from the Northern Nights Star Fest, where I had two solid nights of imaging. The first was cut a little short by a spectacular display of aurora, not that I minded at all.
Most of the night the northern horizon had been aglow. Not terribly bright, but obviously there with occasional pulses within it.
About 1:30AM the glow became much brighter and began to expand upward from the horizon. Soon it was bright enough to cast shadows and was casting pillars upward, starting with an intensely blue streak that was initially mistaken for the onset of a Steve event. By 1:45 intense upward pulsing had begun contained within a bright-edge envelope. Pulses were rapid bright and chaotic, and their areal extent grew to encompass the entire northern half of the sky. My impression of them was driving at high speed through very patchy fog, brightly lit by the car's high-beam headlights. The dominant color was the usual pale green, with some reds in more persistent bright patches closer to the horizon.
The impact of the aurora was quite evident in the stream of two-minute luminance exposures I was taking:
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| Mean pixel brightness during the imaging session. |
Notice that in my impatience I started imaging at 9:18, well before the end of astronomical twilight (9:42) and you can see the sky continuing to darken through my 15th frame at 9:43. At about frame 97 (1:02AM) the sky begins a slow brightening probably due to the aurora. At frame 101 (1:08) the brightening rate begins accelerating.
I was imaging a 2.5 x 1.7 degree field centered on a point between the Crescent Nebula and the Soap Bubble in Cygnus. At 2 AM this was at about 53 degrees altitude directly west. The bright boundary (a curtain?) began moving through the field at about 1:53AM and took perhaps ten to twelve minutes to fully exit. Once clear of my FOV the field was full of pulsations which gradually weakened.
The period of intense auroral activity in the FOV is better seen in this expanded view:
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| Expanded view of auroral interaction with FOV; not the frame numbers have been offset by 120 for better legibility |
By the end of my session at about 3AM the aurora was gradually dimming but still a strong source of natural light pollution. Because the aurora created nasty gradients as it crossed the FOV I'll have to discard those frames, along with others nearby in time.
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Oh, the image I was collecting data for is being processed (see first results later in this post). I don't have much hope for the target (the Soap Bubble Nebula next to the Crescent), so I'm processing the luminance first to see if I can see any sign of it. I have 118 good frames (not quite four hours) after tossing a handful of poor tracking frames and those around the time the aurora was bright.
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Other NNSF personal news:
This was the first time that I performed on-site collection of flat frames (and dark flats). I used NINA's built-in Flat Master to vary my light panel's brightness. This made it possible for all the frames to be one second exposures. Flat Master collects flat darks for all four LRGB channels. Since these are all at the same exposure time, three of the channels' flat darks are redundant. This means a little time wasted, but since this can be done during twilight no harm is done, and the extra files can simply be deleted.
Power consumption was about what was expected. With the laptop-specific battery powering that, the main battery handled the first night's 5.5 hours of mount, dew, and camera cooling with 163Wh. The second night's 4.5 hours consumed 136Wh. This averages to about 30Wh per hour of imaging or a continuous power requirement of 30W, which is the number I wanted to determine for planning my energy use.
Let's apply that to the upcoming Iowa Star Party in the first week of October to see what will be needed. That night there are about 9 hours 23 minutes available for imaging. Let's assume three nights of clear sky, so that's at most about 28 hours of imaging. Sounds great! 28 hours x 30W = 840Wh, which is about 240Wh more than my battery can provide. Therefore, I need either AC or solar for charging. Day length is about 11.5 hours, and let's assume the first and last two hours of daylight is unproductive. That gives 7.5 hours to get that 240Wh. That's 32Wh per hour of daylight if it's to be restored in day, or 16Wh / hour if in two days. I think a 50W solar panel should be up to this charge rate, so I've put my 100W panel up for sale. Now I just need to find a replacement in time for October!
UPDATE: I looked at what was for sale on Amazon and saw that the 50Ah battery I previously purchased was on special with an added dealer discount. By far the simplest solution is to bring a second battery and swap it in after the second night's imaging, or patch it into to my power box through the charging port so the two batteries can operate in parallel, providing almost 1.2KWh. Not only an amazon special, but a 10% off dealer discount, too. I went for it.
As for the laptop-aux battery, it was still at 13.3V rest voltage after the two nights, so it's unlikely to need recharging.
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Just registered for the Iowa Star Party, one of my favorites--when it's not crazy hot and humid as it almost always is when it's in late July or August. I've suggested to them that they might be better off holding it in September, and this year they finally moved it -- to October! The average highs then are around 70 and at night it drops to the upper 40s. That's my kind of weather!
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So how did that soap bubble image turn out? I think "barely there" is the best I can say. Here's the full field at 1/5 scale:
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| 1/5 field LRGB |
Okay, Let's get rid of those stars and look at the central portion of the image:
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| This is a teeny bit better; the Bubble is at lower left, click to enlarge |
It's clearly there and has a hint of the correct color shift toward blue, but it's still nothing close to adequate.
This is based on 3.93 hours of luminance, and each of the RGB channels averaged close to 1.27 hours. What's this in terms of total exposure time? Adding together all the light frames (there were 233) that's about 7 3/4 hours of photons collected. To my way of thinking it's more like 5.2 (3.93 + 1.27) hours. Whatever way you slice it, it wasn't enough, and double (or even triple) the time is going to be desired to make this look halfway decent. It might also be useful to take the luminance a little deeper. So maybe this will be the target for the Iowa Star Party?
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One last thing, it seems to me that Donald Trump has only one purpose in life: The feeding of his own Ego. This is not unusual for politicians (see: Lyndon Johnson) but Trump pushes it to pathological limits. You saw in the "debate" how easily his vanity can be used to manipulate him. This is not a tactic invented by Harris; it's a lesson the world has learned from his interactions with authoritarians such as Putin. Trump envies his abuse of power and would seek to imitate it here, replacing the rule of law with the rule of the iron fist. Because I don't think the Grand Experiment of Democracy has yet to run its full course, I will not cast my vote for someone who seeks to sacrifice it to his need for self-gratification.
Oh, and Trump's policies, particularly toward women, stink.
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That's enough for this post. Have fun everyone! See you in October in Iowa!
