OK, I've got one of those planispheres ordered. Slow learner, so this may take time.
Good stuff. We all started somewhere
I'm still a little confused by flashing vs flaring. I thought that it should only be the tumbling satellites flashing, with the others flaring?
OK, I'll try to dig into this a little more. How satellites reflect Sunlight depends on a few factors. The geometry (and phase angle), the surface doing the reflecting, and the satellite's spin rate. All these things play a role.
Let us discuss a "flare". This is where the reflecting surface is stable. The satellite's rotation matches its journey in orbit to maintain its solar panels to face the Sun and its antennas point in a specific direction. This description fits an operation satellite under control. Communications satellites generally fit this description. So the reflection here "glides" across the surface of the Earth, and if you are on its path, it'll appear to get brighter as the center of the reflection reaches you, arrives at maximum, and then fades away. That's a "flare".
However, if the reflecting surface is small, then the "spot" on the Earth will be small, and the fade-in fade-out might not be visible to the eye. Only the maximum bright part will "flash". Binoculars help here because if you catch a flash with the naked eye and then look with binoculars, you may see the fade out. It all depends on the reflecting surfacing causing the flash/flare in the first place.
Now let us discuss a "flash". As previously noted, some flares could also appear as flashes. However, most flashes would come from decommissioned satellites that have picked up a random(ish) rotation (tumble). This tends to be a bit quicker than a managed satellite's slowly controlled orbit rotation. And again, it has surfaces such as solar panels, antennas, and satellite bus that could cause a reflection. However, due to the speed of the rotation, the beam will pass your spot on Earth (if you are on its path) much faster. The fade in/out times might be very short, thus appearing more like a flash than a fade in/out.
So, that describes the common modes that produce a flash or flare, and we now discuss other factors.
That satellite visibility map is nuts. Approx. 8000 satellites up there as far as I can tell. The planet's pretty big, NZ covers about a twentieth of a percent of it, but there are nearly 1.5% of satellites visible in that one part of the sky? Am I missing something there?
There are around 8,000 operational satellites up there. There's a lot more junk than that. It's estimated that there are approx 30 to 40 thousand pieces of crap in Earth orbit we can detect with radar down to the size of a basketball. Many smaller pieces. This number has been growing for years, but the last decade has seen a massive increase in space launches. So, no, you are "not missing something here", there are more on-orbit "things" than even you approximated.
Back to probability again - is seeing 15 flashes over an hour and a half (and probably only about 40 odd minutes looking at the sky), something you'd expect anywhere? We've done this twice on the trot now, and it's the first time I've seen *any* flashes in the sky.
Probabilities are hard to define when little data is available to formulate a probability. That's what we are doing here: collecting data and trying to match what you see to what's there. It's also important to remember that a flash or flare depends on geometry and phase angle between the observer on Earth, the surface of the satellite doing the reflecting, and where the Sun is. That's what makes a lot of these "seasonal". Take, for example, the "UAP race track" phenomenon. We now know it's Starlink satellites, but those need to be at the right angle to reflect, and the Sun needs to be about 35 to 40 degrees below the horizon. Starlinks higher do reflect the Sun. It's just that the reflected direction doesn't hit the Earth, but it does for those near the horizon. Geometry is set up to cause sightings of what appear to be continuous satellites close to the horizon. Also, some reflections that don't hit the ground are not seen by us, but pilots at height might get a better view
Now consider the Sun's position in all of this. It needs to be 35 to 40 degrees below. That doesn't happen all the time throughout the year. There are times in Autumn when this all lines up, so you get these reports around this time of year.
Here's an example of when someone first noticed this Starlink race track around the same time pilots picked up on it. Look to the bottom right next to the observatory.
(edit:
@Mick West, this video might be a good candidate for your latest version sitrec? The details of time, date and location are in the video description)
I gather from your knowledge of the area, a lot of you most likely spend a bit of time looking up - has anyone else made observations of so many flashes in such short duration periods?
There was an effort long ago to collect data on flashing satellites, but that website appears to have gone. Some positional observers will report when a satellite's brightness varies as it transits the sky, but not all do. The problem is you need to gather a lot of data to analyze just one satellite, and as you've already discovered, there are many of them!
Take the Iriumium Generation 1 satellites (now gone). It was noticed early on that they "randomly" created very bright flares. A few people dug into the phenomena and thanks to Macdonald Douglas providing data about these satellite designs, it was well known that the three antennas maintained a pointing direction as it orbits. From this, computer software was created that predicted them with high accuracy. That's how I took my photo of Iridium 3 a few weeks before it was retired. But this level of knowledge about a satellite is rare. And it's one reason I focused on NAVSTARs. Those retired and mostly of the same design, and it may be possible to learn more. However, other satellites and space junk are "one of a kind" and require much more data. So, I'm hoping you can see this subject is fairly small, and the number of potential variables is high.
So please keep the data coming; it's useful to some of us and goes some way to explaining some of the stuff people can see in the sky.