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Discussion: Starlink group pass tonight

in: biggins; biggins > 2023-09-20

Sep 22, 2023 3:02 AM # 
Sorry for the late notice. There's a compact starlink train pass at 8:37 PM PDT. Look WNW, between the orange star Arcturus and the handle of the big dipper ("follow the arc to Arcturus"). Just saw the same group pass here and it was pretty amazing. Also saw the same group last night. Its 22 sats in a line, about as long as the big dipper itself. Here's the sky chart for Truckee and central CA/NV:

The sats will enter shadow just below overhead. They actually went higher than this chart would indicate - I'd say almost to the head of Draco, so maybe they're already a little higher than when this ephemeris was generated.

This is just a half hour from now! I took some pics with a 70mm telephoto on a tripod. Use big glass and a shortish exp to see the individual dots or go longer for a trail. Binocs are also useful, especially when watching for them to arrive low on the horizon.
Sep 22, 2023 6:27 AM # 
Another nearly identical pass tomorrow night (Fri) at 8:40 PM PDT, a little farther south passing very near Arcturus. The train should be a little longer:

There's another group 6 launch on Sat night, which should set up another similar set of passes next week. Weather looks lousy for us, but might be better for you.

Here's one of the images I got tonight. I count 21 sats here, but the table says there should be 22. Maybe one hiding under another. Was aiming for 1/8" at f/3.2 to minimize trailing, but all my shots were 1/4" and 1/5" Guess I fumbled the knob counts in the dark.

Sep 22, 2023 3:21 PM # 
Ah missed it.
BUT last weekend I was camping in the middle of nowhere up northish, and just as I was going to dive into the tent for the night I saw a starlink train coming up. Got one picture with no prep, let me get it up.
Sep 22, 2023 3:34 PM # 

Just had time to get out the camera, so no time for settings or a tripod or focusing or any of that jazz. Kindof surprised I got it at all. This was freehand almost straight up, then it faded before I could get another one. Brightest I've ever seen them.
Sep 23, 2023 3:01 AM # 
Whoa, nice! They are very blue, aren't they? By eye they look pale green, just like any other faint stars, but the camera doesn't lie. My greyscale image above is raw, un-debayered and then binned 2x2, but the red pixels are almost completely blank. I didn't expect that.

Here's the deployment video of group 6-17. Cool reflection of the falcon upper stage and release mechanism. At least one side of these larger v2 "mini" sats is highly polished. Can't quite tell if those are the solar panels or part of the antenna, or if they are blue-ish. If this is the side facing down right now that would explain why these are glinting in the sun before they enter shadow on these passes.

40 mins to tonight's G6-17 pass for you. It was overcast here. The ones you saw last weekend were probably G6-16, which was launched Friday, Sep 15.
Sep 23, 2023 3:54 AM # 
By the way, the Osiris-Rex asteroid sample return capsule re-entry will be directly above you on Sunday morning:

Info and timeline here:

Looks like atmospheric entry will be at 7:42 AM PDT over the CA coastline and highest temp will be about a minute later over central NV. Its a very fast re-entry. I'd think this would be visible even in daylight and leave a visible trail.
Sep 23, 2023 2:44 PM # 
Saw the starlinks last night! Fairly bright, but normal star-colored white, and the faded before getting very high. Handheld iphone picture.

The ones last weekend really were that blue, even to the naked eye, it was wild.

Morning reentry views aren't likely, we've got thick morning fog here for a couple hours these days.
Sep 24, 2023 12:26 AM # 
Can you climb up above it (recognizing that it'll be very early on a Sunday morning :) ?

Here are some stacks of the sequence of images I took on Thurs. I re-pointed the camera 6 times as they climbed higher. On the left is a straight max combine, and on the right I've offset all 21 images from lowest to highest elevation in the sky:

The color starts out reddish due to atmospheric extinction when very low, but then changes from green to blue with elevation. The highest point was not quite directly overhead, but maybe 50 deg elevation.

I suspect this color change is due to a reflective film they put over the earth facing antennas. It's described as a dielectric mirror or Bragg mirror. It appears to act as an anti-reflection interference filter. My guess is the color change is due to the changing sunlight incidence angle (solar phase) changing through the pass, with the AR efficiency having a wavelength dependence depending on that angle. Like this demonstration from the dielectric mirror wiki page.
Sep 24, 2023 2:07 PM # 
This is the only groundtrack map I could find. Presumably the red part of the line is in the atmosphere. It'll pass S of you but should be relatively high in the sky. The entry capsule was released on time, so they have committed.

Live coverage has started on NASA TV. Landing in Utah expected at ~7:50 AM PDT. They're still expecting atmospheric entry at ~7:40 AM PDT.

Might be able to catch a glimpse on the Truckee airport webcam if it happens to be pointing S-SE at the time.

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