APOD: Big Dipper over Pyramid Mountain (2023 Dec 10)

[APOD Robot]

Big Dipper over Pyramid Mountain

Explanation: When did you first learn to identify this group of stars? Although they are familiar to many people around the world, different cultures have associated this asterism with different icons and folklore. Known in the USA as the Big Dipper, the stars are part of a constellation designated by the International Astronomical Union in 1922 as the Great Bear (Ursa Major). The recognized star names of these stars are (left to right) Alkaid, Mizar/Alcor, Alioth, Megrez, Phecda, Merak, and Dubhe. Of course, stars in any given constellation are unlikely to be physically related. But surprisingly, most of the Big Dipper stars do seem to be headed in the same direction as they plough through space, a property they share with other stars spread out over an even larger area across the sky. Their measured common motion suggests that they all belong to a loose, nearby star cluster, thought to be on average only about 75 light-years away and up to 30 light-years across. The cluster is more properly known as the Ursa Major Moving Group. The featured image captured the iconic stars recently above Pyramid Mountain in Alberta, Canada.

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[Ann]

It's always nice to see the Big Dipper! Although in this picture its shape seems slightly squashed, and the stars are completely colorless.

Big Dipper over Pyramid Mountain. Image Credit & Copyright: Steve Cullen

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Big Dipper. Credit: Bob King.

---

It is indeed interesting that the middle five stars of the Big Dipper all belong to the Ursa Major Moving Group. Not only do they all move in more or less the same direction, but they are located at more or less the same distance from the Earth (~ 80 light-years), and they are all spectral class A stars with relatively similar luminosities.

The two outliers, Alkaid and Dubhe, move in another direction than the five middle stars. So the Big Dipper will inexorably lose its Dipper shape as time goes by.

---

I took the picture from this page. Check it out and see how Orion and Crux will change over time, and see a fun animation of the changing shape of the Big Dipper!

Ann

[Rauf]

It's always nice to see the Big Dipper! Although in this picture its shape seems slightly squashed, and the stars are completely colorless.

Big Dipper over Pyramid Mountain. Image Credit & Copyright: Steve Cullen

---

Big Dipper. Credit: Bob King.

---

It is indeed interesting that the middle five stars of the Big Dipper all belong to the Ursa Major Moving Group. Not only do they all move in more or less the same direction, but they are located at more or less the same distance from the Earth (~ 80 light-years), and they are all spectral class A stars with relatively similar luminosities.

The two outliers, Alkaid and Dubhe, move in another direction than the five middle stars. So the Big Dipper will inexorably lose its Dipper shape as time goes by.

---

I took the picture from this page. Check it out and see how Orion and Crux will change over time, and see a fun animation of the changing shape of the Big Dipper!

Ann

It's weird Ann! But the last link you shared, it wants me to allow notification to confirm I'm not a bot! Not falling for that!

[sc02492]

Although in this picture its shape seems slightly squashed.

Ann

This is a beautiful image. This effect is typical of barrel distortion when using a wide angle lens.

[johnnydeep]

It's always nice to see the Big Dipper! Although in this picture its shape seems slightly squashed, and the stars are completely colorless.

Big Dipper over Pyramid Mountain. Image Credit & Copyright: Steve Cullen

---

Big Dipper. Credit: Bob King.

---

It is indeed interesting that the middle five stars of the Big Dipper all belong to the Ursa Major Moving Group. Not only do they all move in more or less the same direction, but they are located at more or less the same distance from the Earth (~ 80 light-years), and they are all spectral class A stars with relatively similar luminosities.

The two outliers, Alkaid and Dubhe, move in another direction than the five middle stars. So the Big Dipper will inexorably lose its Dipper shape as time goes by.

---

I took the picture from this page. Check it out and see how Orion and Crux will change over time, and see a fun animation of the changing shape of the Big Dipper!

Ann

It's weird Ann! But the last link you shared, it wants me to allow notification to confirm I'm not a bot! Not falling for that!

Yeah, the link is borked for me too. I just get an "internal server error". Ann's pic is broken for me as well: "access denied". I have gotten this many times before for unknown reasons.

I can't find the animation anywhere either. This page has pics of 100000 years ago, now, and 100000 hence:

https://universe2go.com/en/sky-in-100000-years/

[Ann]

I can't find it anymore, either.

You might check out this little video tidbit about the Big Dipper. (Warning: The subtitles claim that stars closer to the center of the galaxy move slower, and stars farther from the center move faster. Whoever wrote the subtitles has been listening too much to those who say that the stars on the outskirts of the Milky Way move fast.)

Click to play embedded YouTube video.

Ann

[VictorBorun]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

[Ann]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

It has to do with the quality of the light. Is the light "evenly distributed", as it is on an overcast day?

Is the light bright overall, and do objects cast shadows, as they do when the Sun is shining?

Is the light "unevenly distributed", as if it came from a relatively weak light source?

Note in the third picture how moonlight is reflected off the roof of a building.

---

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

Ann

[Rauf]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

It has to do with the quality of the light. Is the light "evenly distributed", as it is on an overcast day?


Overcast day 8 December 2023.jpg



Is the light bright overall, and do objects cast shadows, as they do when the Sun is shining?


Bright day 25 November 2023.jpg



Is the light "unevenly distributed", as if it came from a relatively weak light source?


Moonlight reflected on a roof November 1 2023.jpg


Note in the third picture how moonlight is reflected off the roof of a building.

---

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

Ann

I'm wondering what the source of the light is that's making the sky bright in APOD?

[Rauf]

I can't find it anymore, either.

You might check out this little video tidbit about the Big Dipper. (Warning: The subtitles claim that stars closer to the center of the galaxy move slower, and stars farther from the center move faster. Whoever wrote the subtitles has been listening too much to those who say that the stars on the outskirts of the Milky Way move fast.)

Click to play embedded YouTube video.

Ann

I don't know how accurate is it, but moving forward in time using Stellarium allows you to see the changes in constellations over time!

Here's what happened to Cassiopeia:

Cassiopeia in year 10000

Cassiopeia in year 25000

Cassiopeia in year 50000

I wish I could live to see them.

[Ann]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

It has to do with the quality of the light. Is the light "evenly distributed", as it is on an overcast day?


Overcast day 8 December 2023.jpg



Is the light bright overall, and do objects cast shadows, as they do when the Sun is shining?


Bright day 25 November 2023.jpg



Is the light "unevenly distributed", as if it came from a relatively weak light source?


Moonlight reflected on a roof November 1 2023.jpg


Note in the third picture how moonlight is reflected off the roof of a building.

---

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

Ann

I'm wondering what the source of the light is that's making the sky bright in APOD?

If we assume that the picture is reasonably true color, then the brightest parts of the sky are blue (or blue-ish). That would mean that the brightest parts of the sky can't be lit by light pollution, auroras or airglow, because none of these phenomena are blue.

A possible explanation might be that a not-too-bright Moon is rising behind the mountains. If the sky is misty and covered in very light clouds, then the clouds may scatter the light from the Moon. Astrophotographer David Malin has shown that the moonlit night sky is blue.

Thicker clouds may not let the moonlight through, and so appear dark.

I took the picture above through a window pane covered in condensation. You can see the bluish light surrounding the Moon, and the very yellow light of the street light.

Ann

[VictorBorun]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

It has to do with the quality of the light. Is the light "evenly distributed", as it is on an overcast day?


Overcast day 8 December 2023.jpg



Is the light bright overall, and do objects cast shadows, as they do when the Sun is shining?


Bright day 25 November 2023.jpg



Is the light "unevenly distributed", as if it came from a relatively weak light source?


Moonlight reflected on a roof November 1 2023.jpg


Note in the third picture how moonlight is reflected off the roof of a building.

---

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

Ann

I'm wondering what the source of the light is that's making the sky bright in APOD?

IMHO the night feeling has to do with darker blue sky, darker shadows and somewhat lime hue of green trees when we adapt to the scene's white which is every moonlit white or gleaming detail.
And I think the reason is that Moon is brown, or anti-blue.

That's what makes the night blue sky a darker fill-in lamp in relation to the main lamp, deepening all the shadows.
And that's what makes the green trees limer.

Here is my attempt to photoshop this APOD into a day-feeling scene:

All it took was to apply gamma=2 to the green channel and gamma=3 to the blue one

[VictorBorun]

let me try it the other way round, to photoshop a daytime scene

into a nightish-feeling one

[VictorBorun]

Bright day 25 November 2023.jpg

Ann

nightification

gamma .4 for the red chammel, .2 for the green channel, .1 for the blue channel

[Ann]

I'm wondering what the source of the light is that's making the sky bright in APOD?


IMHO the night feeling has to do with darker blue sky, darker shadows and somewhat lime hue of green trees when we adapt to the scene's white which is every moonlit white or gleaming detail.
And I think the reason is that Moon is brown, or anti-blue.

That's what makes the night blue sky a darker fill-in lamp in relation to the main lamp, deepening all the shadows.
And that's what makes the green trees limer.

Here is my attempt to photoshop this APOD into a day-feeling scene:

Click to view full size image

All it took was to apply gamma=2 to the green channel and gamma=3 to the blue one

I still think that looks like a night scene. The reason is that the colors are so washed out. There is a Swedish saying - it might be an American saying too, for all I know: All cats are gray at night.

To me, the bluish cast adds to the feeling of a night scene. I have seen the night sky as blue many times. But the warm yellow hue of sunlight is missing.

Moonlight is actually yellower than sunlight. But because moonlight is so much fainter than sunlight, it doesn't bathe the landscape in a warm yellowish light. Instead, we get the impression that moonlight is silver-colored. And the moonlit landscape looks colorless, silver, or possibly slightly bluish. The impression of blue light is due to a lack of warm bright yellow light.

Click to view full size image

Ann

[Ann]

let me try it the other way round, to photoshop a daytime scene

into a nightish-feeling one

Click to view full size image

Your first picture looks perfectly like a daytime scene. The colors are warm and bright. There are no shadows, but there are clouds in the sky, and the Sun may easily be hidden behind a cloud, muting its light and removing the shadows. I get the feeling that the Sun might come out again at any time.

The second picture does not look like a normal night scene to me at all. It is way too orange. It is possible that the night colors may look like that if there has been an enormous volcanic eruption that has released huge amounts of pollution in the air.

A sunset after the eruption of Krakatau.

---

However, there are clear blue patches in your night sky scene. I don't think there would be any way to get a combination of clear blue and vivid orange in a night scene that isn't lit up by orange neon street lamps (and the neon light may indeed kill the blue hue of the sky):

Click to view full size image

So I don't think you will see a combination of clear blue and vivid orange light at night, if we are talking about "natural" light sources.

You change done of my pictures into this:

Click to view full size image

Indeed, my hometown of Malmö might look like that at night! There are many orange street lamps here. But the light would have to come from a street lamp, not from the Moon. The Moon would never create such a very bright orange light.

The APOD clearly showed us a remote landscape in Canada, where we don't expect to see any bright orange street lamps at all.

Ann

[VictorBorun]

Here is my attempt to photoshop this APOD into a day-feeling scene:

Click to view full size image

All it took was to apply gamma=2 to the green channel and gamma=3 to the blue one

I still think that looks like a night scene. The reason is that the colors are so washed out. There is a Swedish saying - it might be an American saying too, for all I know: All cats are gray at night.

To me, the bluish cast adds to the feeling of a night scene. I have seen the night sky as blue many times. But the warm yellow hue of sunlight is missing.

Moonlight is actually yellower than sunlight. But because moonlight is so much fainter than sunlight, it doesn't bathe the landscape in a warm yellowish light. Instead, we get the impression that moonlight is silver-colored. And the moonlit landscape looks colorless, silver, or possibly slightly bluish. The impression of blue light is due to a lack of warm bright yellow light.

Click to view full size image

Ann

Then I apply gamma=1.41 to the red channel, 2 to the green channel and gamma=2.82 to the blue one
And then apply saturation 20/100

or gamma=1.7 to the red channel, 2.5 to the green channel and gamma=3 to the blue one
And then apply saturation 30/100

[VictorBorun]

There is a Swedish saying - it might be an American saying too, for all I know: All cats are gray at night.
Ann

ok, I apply saturation -50/100 (after moonification)

[Chris Peterson]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

I think that's it. I've seen plenty of nighttime pictures taken when there's a full-ish Moon, and they are indistinguishable from daytime images.

[VictorBorun]

offtopic about colourful scenes at night

I challenge everybody to solve this mystery.
If you zoom in this APOD and see just the bridge, the water and the trees, why do you still feel that it is night?

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

I think that's it. I've seen plenty of nighttime pictures taken when there's a full-ish Moon, and they are indistinguishable from daytime images.

so you don't think that some brownness of Moon is dimming the sky shine and therefore deepening all the shadows (in long exposure colourful nighttime shots) ?

[Chris Peterson]

There are no (sharp) shadows in the APOD, and yet the light is unevenly distributed. The bridge is lit up in a way it wouldn't be if it was daylight on an overcast day. And there would certainly be very obvious shadows if the Sun was shining on the scene.

I think that's it. I've seen plenty of nighttime pictures taken when there's a full-ish Moon, and they are indistinguishable from daytime images.

so you don't think that some brownness of Moon is dimming the sky shine and therefore deepening all the shadows (in long exposure colourful nighttime shots) ?

The Moon isn't all that brown. And no, I don't think we can see minor color shifts. Our brain compensates. The color of everything under fluorescent lamps is radically different than under incandescent lamps, and within a few seconds under either we don't notice. It's only when we place images taken with the same settings side-by-side that we see those color differences.

[VictorBorun]

I think that's it. I've seen plenty of nighttime pictures taken when there's a full-ish Moon, and they are indistinguishable from daytime images.

so you don't think that some brownness of Moon is dimming the sky shine and therefore deepening all the shadows (in long exposure colourful nighttime shots) ?

The Moon isn't all that brown. And no, I don't think we can see minor colour shifts. Our brain compensates. The color of everything under fluorescent lamps is radically different than under incandescent lamps, and within a few seconds under either we don't notice. It's only when we place images taken with the same settings side-by-side that we see those colour differences.

but shadows (filled with sky shine) and moonlit details are side by side
And even moderate brownness should dim the night version of the blue sky

[Chris Peterson]

so you don't think that some brownness of Moon is dimming the sky shine and therefore deepening all the shadows (in long exposure colourful nighttime shots) ?

The Moon isn't all that brown. And no, I don't think we can see minor colour shifts. Our brain compensates. The color of everything under fluorescent lamps is radically different than under incandescent lamps, and within a few seconds under either we don't notice. It's only when we place images taken with the same settings side-by-side that we see those colour differences.

but shadows (filled with sky shine) and moonlit details are side by side
And even moderate brownness should dim the night version of the blue sky

There is no such thing as "brownness". The Moon absorbs a little bit of blue from sunlight, so it creates slightly redder, or warmer, light. It remains effectively white to our eyes, just as the Sun does as the atmospheric path of its light changes (except when very near the horizon).

Images made at night under a full Moon and exposed to produce a sky that is blue are not visually distinguishable from daytime images.

[Ann]

The Moon isn't all that brown. And no, I don't think we can see minor colour shifts. Our brain compensates. The color of everything under fluorescent lamps is radically different than under incandescent lamps, and within a few seconds under either we don't notice. It's only when we place images taken with the same settings side-by-side that we see those colour differences.

but shadows (filled with sky shine) and moonlit details are side by side
And even moderate brownness should dim the night version of the blue sky

There is no such thing as "brownness". The Moon absorbs a little bit of blue from sunlight, so it creates slightly redder, or warmer, light. It remains effectively white to our eyes, just as the Sun does as the atmospheric path of its light changes (except when very near the horizon).

Images made at night under a full Moon and exposed to produce a sky that is blue are not visually distinguishable from daytime images.

Exactly, Chris. But it would be stupid photographing stars under a full Moon. I don't think this image was taken under a full Moon, not even a half Moon.

Ann

[Chris Peterson]

but shadows (filled with sky shine) and moonlit details are side by side
And even moderate brownness should dim the night version of the blue sky

There is no such thing as "brownness". The Moon absorbs a little bit of blue from sunlight, so it creates slightly redder, or warmer, light. It remains effectively white to our eyes, just as the Sun does as the atmospheric path of its light changes (except when very near the horizon).

Images made at night under a full Moon and exposed to produce a sky that is blue are not visually distinguishable from daytime images.

Exactly, Chris. But it would be stupid photographing stars under a full Moon. I don't think this image was taken under a full Moon, not even a half Moon.

Ann

Based on the lack of shadows, I don't think there was any Moon present. But it would be interesting to know the date. In any case, I was addressing the general question of visual differences in day and night images, not this image in particular.