APOD: A Spiral Aurora over Iceland (2021 Sep 12)

[APOD Robot]

A Spiral Aurora over Iceland

Explanation: What's happened to the sky? Aurora! Captured in 2015, this aurora was noted by Icelanders for its great brightness and quick development. The aurora resulted from a solar storm, with high energy particles bursting out from the Sun and through a crack in Earth's protective magnetosphere a few days later. Although a spiral pattern can be discerned, creative humans might imagine the complex glow as an atmospheric apparition of any number of common icons. In the foreground of the featured image is the Ölfusá River while the lights illuminate a bridge in Selfoss City. Just beyond the low clouds is a nearly full Moon. The liveliness of the Sun -- and likely the resulting auroras on Earth -- is slowly increasing as the Sun emerges from a Solar minimum, a historically quiet period in its 11-year cycle.

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[orin stepanek]

AuroraIceland_Necchi_960.jpg

Beautiful Aurora! I wonder if is like a photo
of the solar flair that created it!

imageodxx9.jpg

Mustn't forget Kitty!

[johnnydeep]

A Spiral Aurora over Iceland

Explanation: What's happened to the sky? Aurora! Captured in 2015, this aurora was noted by Icelanders for its great brightness and quick development. The aurora resulted from a solar storm, with high energy particles bursting out from the Sun and through a crack in Earth's protective magnetosphere a few days later. Although a spiral pattern can be discerned, creative humans might imagine the complex glow as an atmospheric apparition of any number of common icons. In the foreground of the featured image is the Ölfusá River while the lights illuminate a bridge in Selfoss City. Just beyond the low clouds is a nearly full Moon. The liveliness of the Sun -- and likely the resulting auroras on Earth -- is slowly increasing as the Sun emerges from a Solar minimum, a historically quiet period in its 11-year cycle.

The statement about the solar wind taking "a few days" to reach Earth from the Sun caught my eye. Does the math work out? Indeed it does:

Using 150000000 km as Earth's distance from the Sun, and an (equatorial) solar wind speed of 400 km/s from WikiPedia, we get about 4.3 days to reach Earth: 4.3 = 150000000 / 400 / 3600 / 24.

Click to view full size image

[neufer]

The statement about the solar wind taking "a few days" to reach Earth from the Sun caught my eye. Does the math work out? Indeed it does:

Using 150000000 km as Earth's distance from the Sun, and an (equatorial) solar wind speed of 400 km/s from WikiPedia, we get about 4.3 days to reach Earth: 4.3 = 150000000 / 400 / 3600 / 24.

The heliospheric current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the solar wind

---

A solar sidereal rotation period (at equator) ~25 days makes for Archimedean spirals of spiral width: ~5.8 AU = 25 d/4.3 d.

[johnnydeep]

The statement about the solar wind taking "a few days" to reach Earth from the Sun caught my eye. Does the math work out? Indeed it does:

Using 150000000 km as Earth's distance from the Sun, and an (equatorial) solar wind speed of 400 km/s from WikiPedia, we get about 4.3 days to reach Earth: 4.3 = 150000000 / 400 / 3600 / 24.

The heliospheric current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the solar wind

---

A solar sidereal rotation period (at equator) ~25 days makes for Archimedean spirals of spiral width: ~5.8 AU = 25 d/4.3 d.

Probably cool , but I don't understand the significance of the 5.8 AU figure. According to https://en.wikipedia.org/wiki/Heliosphe ... rent_sheet:

The heliospheric current sheet[1] is the surface in the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere.[2][3] The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (solar wind).[4] A small electrical current flows within the sheet, about 10−10 A/m2. The thickness of the current sheet is about 10,000 km near the orbit of the Earth.

The picture of the purple sheet seems to represent the entire sheet as exists throughout the solar system (assuming the dots in orbit around the sun are planets). Where exactly does the particular orbital distance of the earth come into play to influence anything?

[neufer]

The statement about the solar wind taking "a few days" to reach Earth from the Sun caught my eye. Does the math work out? Indeed it does:

Using 150000000 km as Earth's distance from the Sun, and an (equatorial) solar wind speed of 400 km/s from WikiPedia, we get about 4.3 days to reach Earth: 4.3 = 150000000 / 400 / 3600 / 24.

A solar sidereal rotation period (at equator) ~25 days makes for Archimedean spirals of spiral width: ~5.8 AU = 25 d/4.3 d.

Probably cool , but I don't understand the significance of the 5.8 AU figure.
According to https://en.wikipedia.org/wiki/Heliosphe ... rent_sheet:

The heliospheric current sheet is the surface in the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere. The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (solar wind). A small electrical current flows within the sheet, about 10−10 A/m2. The thickness of the current sheet is about 10,000 km near the orbit of the Earth.

The picture of the purple sheet seems to represent the entire sheet as exists throughout the solar system (assuming the dots in orbit around the sun are planets). Where exactly does the particular orbital distance of the earth come into play to influence anything?

The magnetic field cannot easily pass through conducting plasma fields.

Hence it is stuck between:

• 1) the solar plasma fields rotating once every 25 days and
  2) the solar wind plasma fields moving radially at 1 AU / 4.3 days.

[johnnydeep]

A solar sidereal rotation period (at equator) ~25 days makes for Archimedean spirals of spiral width: ~5.8 AU = 25 d/4.3 d.

Probably cool , but I don't understand the significance of the 5.8 AU figure.
According to https://en.wikipedia.org/wiki/Heliosphe ... rent_sheet:

The heliospheric current sheet is the surface in the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere. The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (solar wind). A small electrical current flows within the sheet, about 10−10 A/m2. The thickness of the current sheet is about 10,000 km near the orbit of the Earth.

The picture of the purple sheet seems to represent the entire sheet as exists throughout the solar system (assuming the dots in orbit around the sun are planets). Where exactly does the particular orbital distance of the earth come into play to influence anything?

The magnetic field cannot easily pass through conducting plasma fields.

Hence it is stuck between:

• 1) the solar plasma fields rotating once every 25 days and
  2) the solar wind plasma fields moving radially at 1 AU / 4.3 days.

Ok, I see now that that the shape of the heliospheric current sheet has absolutely nothing to do with any of the planets as I was wrongly assuming. You're just describing a way to characterize the sheet at a given distance from the Sun given the speed of the solar wind.