Starship Asterisk*

Chris Peterson wrote: ↑Tue Nov 10, 2020 5:14 am

dx_ray wrote: ↑Tue Nov 10, 2020 12:33 am

Chris Peterson wrote: ↑Mon Nov 09, 2020 9:25 pm

The caption is very clear that the image is a composite of three exposures. That is normal photographic technique for any high dynamic range subject.

HDR should not affect stars. Please zoom in to 100% and take a closer look. Stars are messed up due to the manipulation. Can you recognize any constellations from this image?

There are many ways to capture wide dynamic range other than conventional HDR. I've seen a great many nighttime images that make it very difficult to detect constellations.

dx_ray wrote: ↑Tue Nov 10, 2020 12:33 am

Chris Peterson wrote: ↑Mon Nov 09, 2020 9:25 pm

dx_ray wrote: ↑Mon Nov 09, 2020 6:26 pm This is NOT an honest astrophotography. If you zoom in the image, you can see many manipulations, like patches with different size of noise, or star dots in different sizes. This means that, those patches come from different images. I guess such manipulation is to make the circular shape of the aurora.


https://apod.nasa.gov/apod/lib/apsubmit2015.html

APOD has post this image several times, I think such manipulation should not be shown on APOD.

The caption is very clear that the image is a composite of three exposures. That is normal photographic technique for any high dynamic range subject.

HDR should not affect stars. Please zoom in to 100% and take a closer look. Stars are messed up due to the manipulation. Can you recognize any constellations from this image?

gcvisel@gmail.com wrote: ↑Tue Nov 10, 2020 1:30 am
Is there a flow of electricity happening with all those ions passing through?

https://en.wikipedia.org/wiki/Birkeland_current wrote:

Schematic of the Birkeland or Field-Aligned Currents and the ionospheric current systems they connect to, Pedersen and Hall currents.

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<<A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth's magnetosphere to the Earth's high latitude ionosphere. In the Earth's magnetosphere, the currents are driven by the solar wind and interplanetary magnetic field and by bulk motions of plasma through the magnetosphere (convection indirectly driven by the interplanetary environment). The strength of the Birkeland currents changes with activity in the magnetosphere (e.g. during substorms). Small scale variations in the upward current sheets (downward flowing electrons) accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the Auroras Borealis and Australis. In the high latitude ionosphere (or auroral zones), the Birkeland currents close through the region of the auroral electrojet, which flows perpendicular to the local magnetic field in the ionosphere. The Birkeland currents occur in two pairs of field-aligned current sheets. One pair extends from noon through the dusk sector to the midnight sector. The other pair extends from noon through the dawn sector to the midnight sector. The sheet on the high latitude side of the auroral zone is referred to as the Region 1 current sheet and the sheet on the low latitude side is referred to as the Region 2 current sheet.

The currents were predicted in 1908 by Norwegian explorer and physicist Kristian Birkeland, who undertook expeditions north of the Arctic Circle to study the aurora. He rediscovered, using simple magnetic field measurement instruments, that when the aurora appeared the needles of magnetometers changed direction, confirming the findings of Anders Celsius and assistant Olof Hjorter more than a century before. This could only imply that currents were flowing in the atmosphere above. He theorized that somehow the Sun emitted a cathode ray, and corpuscles from what is now known as a solar wind entered the Earth's magnetic field and created currents, thereby creating the aurora. This view was scorned by other researchers, but in 1967 a satellite, launched into the auroral region, showed that the currents posited by Birkeland existed. In honour of him and his theory these currents are named Birkeland currents.

Auroral Birkeland currents carry about 100,000 amperes during quiet times and more than 1 million amperes during geomagnetically disturbed times. Birkeland had estimated currents "at heights of several hundred kilometres, and strengths of up to a million amperes" in 1908. The ionospheric currents that connect the field-aligned currents give rise to Joule heating in the upper atmosphere. The heat is transferred from the ionospheric plasma to the gas of the upper atmosphere, which consequently rises and increases drag on low-altitude satellites.

Birkeland currents are also one of a class of plasma phenomena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. This can also twist, producing a helical pinch that spirals like a twisted or braided rope, and this most closely corresponds to a Birkeland current. Pairs of parallel Birkeland currents will also interact due to Ampère's force law: parallel Birkeland currents moving in the same direction will attract each other with an electromagnetic force inversely proportional to their distance apart whilst parallel Birkeland currents moving in opposite directions will repel each other. There is also a short-range circular component to the force between two Birkeland currents that is opposite to the longer-range parallel forces.>>

gcvisel@gmail.com wrote: ↑Tue Nov 10, 2020 1:30 am
Why do (vivid) aurora look like curtains? Is that a map of the magnetic field there?

https://en.wikipedia.org/wiki/Aurora#Forms_of_auroras

Different Aurora forms

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Click to play embedded YouTube video.

<<According to Clark (2007), there are four main Aurora forms that can be seen from the ground, from least to most visible:

• A mild glow, near the horizon. These can be close to the limit of visibility, but can be distinguished from moonlit clouds because stars can be seen undiminished through the glow.
  
  Patches or surfaces that look like clouds.
  
  Arcs curve across the sky.
  
  Rays are light and dark stripes across arcs, reaching upwards by various amounts.
  
  Coronas cover much of the sky and diverge from one point on it.

Brekke (1994) also described some auroras as curtains. The similarity to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are also known as discrete auroras, which are at times bright enough to read a newspaper by at night.

These forms are consistent with auroras' being shaped by Earth's magnetic field. The appearances of arcs, rays, curtains, and coronas are determined by the shapes of the luminous parts of the atmosphere and a viewer's position.>>

Chris Peterson wrote: ↑Mon Nov 09, 2020 9:25 pm

dx_ray wrote: ↑Mon Nov 09, 2020 6:26 pm This is NOT an honest astrophotography. If you zoom in the image, you can see many manipulations, like patches with different size of noise, or star dots in different sizes. This means that, those patches come from different images. I guess such manipulation is to make the circular shape of the aurora.

Ethics statement: APOD accepts composited or digitally manipulated images, but requires them to be identified as such and to have the techniques used described in a straightforward, honest and complete way.

https://apod.nasa.gov/apod/lib/apsubmit2015.html

APOD has post this image several times, I think such manipulation should not be shown on APOD.

The caption is very clear that the image is a composite of three exposures. That is normal photographic technique for any high dynamic range subject.

MarkBour wrote: ↑Mon Nov 09, 2020 10:26 pm
So where would this place the photographer and his daring subject?

Somewhere near Pilan peak.

Google Earth around Pilan peak makes it appear more accessible than the APOD would suggest, but actually, I have no idea how difficult it is. I wouldn't trust Google Earth over a reliable topo map.

AllTrails rates the trek to Pilan as difficult.

BillBixby wrote: ↑Mon Nov 09, 2020 9:51 pm

orin stepanek wrote: ↑Mon Nov 09, 2020 12:29 pm Nice Aurora! I would never stand on that peak!

Human lightning rod. Add a kite and a key for a simple experiment...

orin stepanek wrote: ↑Mon Nov 09, 2020 12:29 pm Nice Aurora! I would never stand on that peak!

dx_ray wrote: ↑Mon Nov 09, 2020 6:26 pm This is NOT an honest astrophotography. If you zoom in the image, you can see many manipulations, like patches with different size of noise, or star dots in different sizes. This means that, those patches come from different images. I guess such manipulation is to make the circular shape of the aurora.

Ethics statement: APOD accepts composited or digitally manipulated images, but requires them to be identified as such and to have the techniques used described in a straightforward, honest and complete way.

https://apod.nasa.gov/apod/lib/apsubmit2015.html

APOD has post this image several times, I think such manipulation should not be shown on APOD.

Ethics statement: APOD accepts composited or digitally manipulated images, but requires them to be identified as such and to have the techniques used described in a straightforward, honest and complete way.

Ann wrote: ↑Mon Nov 09, 2020 6:56 am

WWW wrote: ↑Mon Nov 09, 2020 6:23 am
Are they sure that isn't Mount Crumpit?

Well, they are similar...but on Mount Crumpit it is usually only the Grinch that is green.

https://tinyurl.com/y6k4eod7 wrote:

Austnesfjorden fjord arm

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<<Austnesfjorden is a fjord arm of the Vestfjord on the southeast side of Austvågøya in Vågan municipality in Lofoten . On the west side, from the north, Vestpollen , Sildpollen , Vatterfjorden and the bay Husvågen go off, while Austpollen goes off Austnesfjorden in the northeast. Local road on the east side to the somewhat smaller village Liland.>>

WWW wrote: ↑Mon Nov 09, 2020 6:23 am Are they sure that isn't Mount Crumpit?