u/petecasso0619

If we were to detect a long period comet say close to the size of Greenland with less than one year notice headed directly for Earth is there anything that we could do about it to deflect its course?

When I tried to answer this question myself the answer I got was grim and basically said “forget it, with current technology it will be complete sterilization of life on the surface of the earth”. So maybe some experts can point out something? If not with technology today, what would it take besides early detection? Or is that really the only defense?

Would Earth as a planet survive the impact?

The moral obligation is interesting to me. Would governments just not say anything because there’s nothing we can do about it?

As astronomers, what is your role here? How do you inform agencies?

At least in the US even if astronomers detected it, the anti-science movement which includes a very large portion of citizens would likely ignore it and just deny, deny, deny, but other parts of the world might believe what they actually see.

The Spindle Galaxy located about 44 million light years from Earth in the Draco constellation. Classified as a lenticular galaxy.

M102 - The Spindle Galaxy

OTA: ZWO FF130

Mount: ZWO AM7 with apetura anchor pier

Sensor: ZWO ASI2600MM (mono with Electronic Filter Wheel) LRGB

ZWO Electronic Auto Focuser Pro

Luminance ~5 hours

Red/Green/Blue ~1 hour each

Bortle 7

Processed in Siril and Gimp

I want to start with the obvious. yes cleaning the filters helps and can mitigate the problem. Flats should do this too. I am looking for the technical reason as to why my flats are not correcting fully besides “clean your filters”. Dust on the filters is not the reason cal is broken.

I have had much worse dust clean up very nicely with proper calibration on other rigs so I am trying to get at the root cause of the failed calibration with this setup.

My setup is this:

ZWO FF130 Refractor NO reducer. 1000mm focal length. No flattener because the FF130 is a Petzval Quadruplet (integrated flattener).
ASI2600 MM DUO (integrated guider)
ZWO 7 EFW bolted onto the camera
ZWO AM7 mount
ZWO EAF Pro

I have tried taking flats right before I start imaging and I have tried right after. In both cases the imaging train is fixed. I leave it alone and attached to the OTA. I image the same object night after night and the “goto” feature in the asinair app shows perfect alignment (rotation angle) with the previous night image. Because I image overnight, the autofocus routine does run. In the logs the focus position changes some but not drastic (10s of steps) as a result of temperature fluctuations. That could be a contributor and if it is the reason not sure what to do.

In this case I am only dealing with the Luminance filter for now.

I use Siril histogram preview stretch. What I am seeing is that before cal there are obvious dust motes that are visible. After cal, they mostly go away - most disappear completely.

It is when I stack that the dust reveals itself again. After stacking the larger dust motes (further from the sensor) are the ones that seem to reveal themselves more prominently. They are circular in shape as you would expect. On one side of the circle is a thin crescent darker moon and on the other side the crescent moon is a a little bit lighter. Signs of improper calibration. These larger circles are not in the corners of the image, they are distributed somewhat evenly across the image.

When I look at the master flat you can visually see the dust motes match up with the light sub. The Luminance filter master flat has a capture time of 750ms with a mean ADU of 29000, standard deviation of about 260 ADU and a min of 256 ADU.
I use an LED panel that I have used on other setups. The stretched flat looks as I expect it to. I have tried dark-flats and I have tried calibrating without darks at all. I feel like I can safely rule the darks out. With or without the darks very little changes after stacking under a heavy stretch. So it seems to rule out darks (I use matching darks gain 100 -10 degree C temp 180 second exposure).

What is interesting is that the blue filter exhibits the problem the least, after stacking the image looks clean for the most part. The Luminance is the worst.

Besides cleaning the filter (fully expect to see that comment) what other reasons could cause this? Why isn’t it correcting fully?

I did realize that I am dithering 5 pixels every 3 frames. Each frame is 180 seconds. Maybe the pattern can be uncorrelated with larger dithering? I have a few cloudy nights to gather some reasons and try things.

Any suggestions?