APOD: The Edge of Space (2021 Jul 24)

[APOD Robot]

The Edge of Space

Explanation: Where does space begin? For purposes of spaceflight some would say at the Karman line, currently defined as an altitude of 100 kilometers (60 miles). Others might place a line 80 kilometers (50 miles) above Earth's mean sea level. But there is no sharp physical boundary that marks the end of atmosphere and the beginning of space. In fact, the Karman line itself is near the transition between the upper mesophere and lower thermosphere. Night shining or noctilucent clouds are high-latitude summer apparitions formed at altitudes near the top of the mesophere, up to 80 kilometers or so, also known as polar mesopheric clouds. Auroral bands of the northern (and southern) lights caused by energetic particles exciting atoms in the thermosphere can extend above 80 kilometers to over 600 kilometers altitude. Taken from a cockpit while flying at an altitude of 10 kilometers (33,000 feet) in the realm of stratospheric aeronautics, this snapshot captures both noctilucent clouds and aurora borealis under a starry sky, looking toward planet Earth's horizon and the edge of space.

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[shaileshs]

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth") ? Just a thought..I'm curious what others think..

[Ann]

I find the APOD amazing. Its colors are amazing, and the way it divides the Earth's atmosphere into layers by colors is amazing, and the sharp starry background is beautiful.

This is what I can see in the image:

1: A dark cloud cover over the Earth seen from above.

2: Orange sunset light.

3: Noctilucent clouds.

4: The deep blue color of the sky after sunset.

5: Yellow and green auroras.

6: Red auroras.

7: A blue aurora, poking up high into the sky over the red aurora?

8: The dividing line between "blue-tinted deep sky" and "black deep sky"?

9: The Double Cluster in Perseus.

10: The Andromeda Galaxy.

11 M33, the Triangulum Galaxy.

12: Alpheratz, Alpha Andromeda, looking almost shockingly blue here!

Ann

[E D Gage]

Thank you, Ann. I thought I detected the Andromeda Galaxy in this lovely photo. But you have mapped out greatly more than that for this amateur. Even Triangulum. Thanks!

[VictorBorun]

I wonder what those red-orange lights are.
Can they be transparent thinnings in the black-thick cloud layer passing rays from low set sun?

[Deathfleer]

Aik? I thought it was the space of the space and time . That space is very mysterious to me. Can't imagine where it is going to end. Does it just enclose the universe or is it far beyond the universe . Was it present and very small at the time before the big bang. These questions, I think will remain unanswered.

[VictorBorun]

Thank you, Ann. I thought I detected the Andromeda Galaxy in this lovely photo. But you have mapped out greatly more than that for this amateur. Even Triangulum. Thanks!

do I get it right?

[Ann]

Thank you, Ann. I thought I detected the Andromeda Galaxy in this lovely photo. But you have mapped out greatly more than that for this amateur. Even Triangulum. Thanks!

do I get it right?

Click to view full size image

You do, Victor.

I just edited my annotated image to include Beta Andromeda. It is number 13 in my image. This bright orange star is located right between Andromeda and M33. If you can find Andromeda and Beta And, you just keep going in the same direction from Beta And until you are as far away from this star as Andromeda is from Beta Andromeda.

That's where you find M33.

Ann

[orin stepanek]

Beautiful! When called the edge of space; my mind was thinking 13,
or 14 billion LY away! Then I read today's APOD! anyway;
kudos to Ralf Rohner; great photo!

[VictorBorun]

7: A blue aurora, poking up high into the sky over the red aurora?

Why, Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity.[27] The molecular nitrogen transitions are much faster than the atomic oxygen ones.

But cool hues, pale cyan to blue to dark violet, are expected for the part of the sky at larger angles from sun. The shortwave photons are closer to the size of air molecules (though the molecules are still a thousand times smaller than the wavelength. That's the reason why Sun looks brighter than the skyshine) and are expected to scatter at a wider angle.

What should be the borderline between the deep violet skyshine and the blackness of the space when the observer is at a 10 km altitude? I think the picture is different from the surface experience. The skyshine that persists is somewhat closer to Sun. No dark violet at the point of the horizon opposite to Sun. Some 15° from Sun as we can see here is as far as it spreads.

Here I squeeze the dark violet patch by setting RGB black level threshold of 0 96 96/255 instead of 0 0 0/255

[neufer]

Wonder what those red-orange lights are.

Ralf Rohner: A dancing Aurora Borealis and Noctilucent clouds captured over the polar dawn
from a Boeing 777-300ER during cruise in the region of Winnipeg, Canada.

Noctilucent clouds means that this is a (probable recent) summertime picture.

No doubt those red-orange "lights" are Manitoba forest fires:
https://earthobservatory.nasa.gov/image ... th-america

[johnnydeep]

AuroraNoctilucent33k_rohner1024.jpg

Beautiful! When called the edge of space; my mind was thinking 13,
or 14 billion LY away! Then I read today's APOD! anyway;
kudos to Ralf Rohner; great photo!

In one - perhaps the only accurate - sense, space penetrates all matter, and matter just occupies it, in some places more densely than in others. I'd say that space suffuses everything, unlike say, a body in water, which displaces it (if it doesn't absorb it). Hmm, can space be displaced? It can certainly be bent by matter.

[neufer]

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth") ? Just a thought..I'm curious what others think..

A view of "full earth shape"?

So...high enough to observe the full disk?

Possible rendering of Anaximander's world map

---

<<In early Mesopotamian mythology, the world was portrayed as a flat disk floating in the ocean with a hemispherical sky-dome above, and this forms the premise for early world maps like those of Anaximander and Hecataeus of Miletus.

Anaximander (Greek: Ἀναξίμανδρος Anaximandros; c. 610 – c. 546 BC) was the first to conceive a mechanical model of the world. In his model, the Earth floats very still in the centre of the infinite, not supported by anything. It remains "in the same place because of its indifference", a point of view that Aristotle considered ingenious, but false. Its curious shape is that of a cylinder with a height one-third of its diameter. The flat top forms the inhabited world, which is surrounded by a circular oceanic mass.

Anaximander's realization that the Earth floats free without falling and does not need to be resting on something has been indicated by many as the first cosmological revolution and the starting point of scientific thinking. Karl Popper calls this idea "one of the boldest, most revolutionary, and most portentous ideas in the whole history of human thinking." Such a model allowed the concept that celestial bodies could pass under the Earth, opening the way to Greek astronomy.>>

[Chris Peterson]

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth") ? Just a thought..I'm curious what others think..

I can do that from a ladder. It depends upon what percentage of a hemisphere you want to require to be visible. Even from low Earth orbit, much of the hemisphere below you is over the horizon.

[neufer]

Main Street in Guffey.

---

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth")?

I can do that from a ladder.

A ladder in Guffey
(Perhaps if you attached a GoPro to chicken & released
her from a velvet-lined mailbox atop a 10' platform.)

Possibly from Mount Sunflower.
https://www.syfy.com/tags/bad-astronomy

[shaileshs]

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth") ? Just a thought..I'm curious what others think..

I can do that from a ladder. It depends upon what percentage of a hemisphere you want to require to be visible. Even from low Earth orbit, much of the hemisphere below you is over the horizon.

Chris, I meant FULL shape of earth in view. Full circle. The Quora article below says Google Earth shows it at around 11000Km..
https://www.quora.com/How-far-one-needs ... s-a-sphere

[Chris Peterson]

Maybe a point from where one has a view of "full earth shape* can be considered as a boundary ("beginning of space around Earth") ? Just a thought..I'm curious what others think..

I can do that from a ladder. It depends upon what percentage of a hemisphere you want to require to be visible. Even from low Earth orbit, much of the hemisphere below you is over the horizon.

Chris, I meant FULL shape of earth in view. Full circle. The Quora article below says Google Earth shows it at around 11000Km..
https://www.quora.com/How-far-one-needs ... s-a-sphere

In order to see one full hemisphere of the Earth, you need to be infinitely far away from it. So like I said, it comes down to what fraction you want to see. Which is another arbitrary value.

[VictorBorun]

Its curious shape is that of a cylinder with a height one-third of its diameter. The flat top forms the inhabited world, which is surrounded by a circular oceanic mass.

I very much doubt this picture from later re-tellers.

One plausible reason why would an ancient Greek suggest Earth be a cylinder is to account for Lunar eclipses. By the time of Aristotle the topic of Lunar eclipses got elaborated up to the extent as to prove that the Earth must cast a circular shadow at any angle of illumination from Sun and therefore must be a sphere. This way Aristotle killed the very poetic and tragic metaphor by Plato of prisoners in a cave who can not really guess the shape of passing things by their shadows.

But speaking of earlier philosopher Anaximander, we must take into account his views on the planets and their orbits as a tyre-like thoruses of black-burnt air containing fire and throwing light from a small transparent spot in such a tyre. No theory of Moon illuminated by Sun and eclipsed by Earth.

Anaximander's plausible reason why make Earth a cylinder is to account for visibility of some constellations only for a southern observer like in Egypt. This kind of reasoning puts the inhabited world on a bulging surface; east to west the surface still could be flat, and that leads a thinker to a cylinder.

[neufer]

Its curious shape is that of a cylinder with a height one-third of its diameter. The flat top forms the inhabited world, which is surrounded by a circular oceanic mass.

Anaximander's plausible reason why make Earth a cylinder is to account for visibility of some constellations only for a southern observer like in Egypt. This kind of reasoning puts the inhabited world on a bulging surface; east to west the surface still could be flat, and that leads a thinker to a cylinder.

• Anaximander clearly believed that people inhabited the flat top of a cylinder and
  that if some constellations were only visible for a southern observer that simply meant
  that they happened to live more directly underneath those close constellations
  (i.e., a significant star parallax effect).

<<Anaximander's theories were influenced by the Greek mythical tradition, and by some ideas of Thales [Thales of Miletus (624 –  546 BC) thought the Earth must be a flat disk which is floating in an expanse of water] as well as by observations made by older civilizations in the Near East, especially Babylon. All these were developed rationally. In his desire to find some universal principle, he assumed, like traditional religion, the existence of a cosmic order.>>

[neufer]

It depends upon what percentage of a hemisphere you want to require to be visible.
Even from low Earth orbit, much of the hemisphere below you is over the horizon.

Chris, I meant FULL shape of earth in view. Full circle.

The Quora article below says Google Earth shows it at around 11000Km..
https://www.quora.com/How-far-one-needs ... s-a-sphere

In order to see one full hemisphere of the Earth, you need to be infinitely far away from it.
So like I said, it comes down to what fraction you want to see. Which is another arbitrary value.

At H=11000 km one can to observe H/(H+R) = 0.63 = 63% of a hemisphere at any given time.

Geostationary satellites (H=35,786 km) can observe
H/(H+R) = 0.849 = 84.9% of a hemisphere
[up to latitudes of arccos(1.00 - 0.849) = 81.3º]
such that 3 Geostationary satellites cover the Earth quite well.

Bezos's New Shepard 4 went to H=107 km so as to observe just H/(H+R) = 1.65% of a hemisphere
out to distances of (10,000 km/90º) x arccos(1.00 - 0.0165) = 1,160 km.

(Chris's 3m ladder might allow him to observe ~ 120 km² from atop Mount Sunflower.)
.............................................................................................
Note, however, that: Sun stationary Earth polar satellites fly at an altitude of 834 km:

• https://en.wikipedia.org/wiki/NOAA-20
  https://en.wikipedia.org/wiki/Suomi_NPP

which allows them to observe H/(H+R) = 0.11 = 11% of a hemisphere at any given time.

Nevertheless, since their full 2arccos(1.00 - 0.11) = 54.25º (6,000 km) wide scans
of the Earth are constantly moving N/S (while the Earth rotates W/E underneath)
after 14 (101.44 min) orbits the entire Earth's surface gets observed at least twice a day.

[orin stepanek]

AuroraNoctilucent33k_rohner1024.jpg

Beautiful! When called the edge of space; my mind was thinking 13,
or 14 billion LY away! Then I read today's APOD! anyway;
kudos to Ralf Rohner; great photo!

In one - perhaps the only accurate - sense, space penetrates all matter, and matter just occupies it, in some places more densely than in others. I'd say that space suffuses everything, unlike say, a body in water, which displaces it (if it doesn't absorb it). Hmm, can space be displaced? It can certainly be bent by matter.

I was thinking edge of the atmosphere!

[VictorBorun]

• Anaximander clearly believed that people inhabited the flat top of a cylinder and
  that if some constellations were only visible for a southern observer that simply meant
  that they happened to live more directly underneath those close constellations
  (i.e., a significant star parallax effect).

Reference here "A column of stone", Aetius reports in ... (III, 10). is not as solid as, say, Aristotle's report on early cosmology by Anaximander.

Thales [Thales of Miletus (624 –  546 BC) thought the Earth must be a flat disk which is floating in an expanse of water] as well as by observations made by older civilizations in the Near East, especially Babylon. All these were developed rationally. In his desire to find some universal principle, he assumed, like traditional religion, the existence of a cosmic order.>>

rather than assuming that earthquakes were the result of supernatural whims, Thales explained them by hypothesizing that the Earth floats on water and that earthquakes occur when the Earth is rocked by waves

I see no Flat Earth by Thales of Miletus.
1) to replace a Great Turtle or a Ring of Elephants, Thales made a water body the earth-quaker. Those theories are weak, they do not predict the next disaster at all. Anyhow there is no connection to any Flat Earth. (In fact we have in the frost zone of the Solar System some spherical bodies with their crust of dust and ice floating over salt water mantle and the liquid water is the quaker here)

2) some reconstruct Thales's method for an observer at the sea shore to range a faraway ship in the sea as based on the mapping the observer's altitude to the horizon's distance. Given some shores are South to North and others are East to West this reconstruction suggests Earth bulging spherically. Moreover Thales was no Anaximander, Thales was famous for predicting eclipses, and this art makes one familiar with Earth's shadows on Moon. So Moon can not shine like a transparent spot in an Anaximander's black-burnt air tyre of orbit; Moon must reflect the sunshine and show Earth's form by shadow in the moment of a Lunar Eclipse.

[ozalba]

Thank you, Ann. I thought I detected the Andromeda Galaxy in this lovely photo. But you have mapped out greatly more than that for this amateur. Even Triangulum. Thanks!

do I get it right?

Click to view full size image

You do, Victor.

The edge of space annotated.png

I just edited my annotated image to include Beta Andromeda. It is number 13 in my image. This bright orange star is located right between Andromeda and M33. If you can find Andromeda and Beta And, you just keep going in the same direction from Beta And until you are as far away from this star as Andromeda is from Beta Andromeda.

That's where you find M33.

Ann

Look really closely, and you can see M31's dwarf companions as well.

[VictorBorun]

It's hardly a pure chance that we get to see Andromeda and Triangulum galaxies no more then 30° from edge-on and roughly aligned with Milky Way that we see exactly edge-on.
Local Cluster, when tidally squeezed out of a parental filament by giant Maffei I galaxy, got a spin along the filament and the line to Maffei I.
All three gas disks of Milky Way, Andromeda and Triangulum as well as their orbits in Local Cluster are spinning roughly in this direction

[neufer]

It's hardly a pure chance that we get to see Andromeda and Triangulum galaxies no more then 30° from edge-on and roughly aligned with Milky Way that we see exactly edge-on.

Local Cluster, when tidally squeezed out of a parental filament by giant Maffei I galaxy, got a spin along the filament and the line to Maffei I.

All three gas disks of Milky Way, Andromeda and Triangulum as well as their orbits in Local Cluster are spinning in this direction

---

Maffei 1 (UGCA 34) elliptical galaxy

---

<<The IC 342/Maffei Group (also known as the IC 342 Group or the Maffei 1 Group) is the nearest group of galaxies to the Local Group. The group can be described as a binary group; the member galaxies are mostly concentrated around either IC 342 or Maffei 1, both of which are the brightest galaxies within the group. The group is part of the Virgo Supercluster. As seen from Earth, the group lies near the plane of the Milky Way (a region sometimes called the Zone of Avoidance). Consequently, the light from many of the galaxies is severely affected by dust obscuration within the Milky Way. This complicates observational studies of the group, as uncertainties in the dust obscuration also affect measurements of the galaxies' luminosities and distances as well as other related quantities

Since the IC 342/Maffei Group and the Local Group are located physically close to each other, the two groups may have influenced each other's evolution during the early stages of galaxy formation. An analysis of the velocities and distances to the IC 342/Maffei Group as measured by M. J. Valtonen and collaborators suggested that IC 342 and Maffei 1 were moving faster than what could be accounted for in the expansion of the universe. They therefore suggested that IC 342 and Maffei 1 were ejected from the Local Group after a violent gravitational interaction with the Andromeda Galaxy during the early stages of the formation of the two groups.

However, this interpretation is dependent on the distances measured to the galaxies in the group, which in turn is dependent on accurately measuring the degree to which interstellar dust in the Milky Way obscures the group. More recent observations have demonstrated that the dust obscuration may have been previously overestimated, so the distances may have been underestimated. If these new distance measurements are correct, then the galaxies in the IC 342/Maffei Group appear to be moving at the rate expected from the expansion of the universe, and the scenario of a collision between the IC 342/Maffei Group and the Local Group would be implausible.>>