APOD: Big Dipper over Pyramid Mountain (2017 Nov 21)

[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]

Nice Dipper, although some of the stars, for example Alkaid, look a little bit elongated.

Ann

[Case]

… constellation designated by the International Astronomical Union in 1922 …

Celestial nomenclature had long been a controversial topic. At its inaugural meeting in May 1922 in Rome, the IAU standardized the constellation names and three-letter abbreviations. (So, for instance, Ursa Major is abbreviated to UMa.) Ejnar Hertzsprung had suggested (and personally used for years) two-letter abbreviations and Henry Norris Russell had compiled an alternative list of three-letter abbreviations. (Yes, the same guys that made the famous diagram.)
Originally the constellations were defined informally by the shapes made by their star patterns, but, as the pace of celestial discoveries quickened in the early 20th century, astronomers decided it would be helpful to have an official set of constellation boundaries. One reason was to aid in the naming of new variable stars, which are named for the constellation in which they reside, so it is important to agree where one constellation ends and the next begins. Eugène Delporte originally listed the 88 “modern” constellations on behalf of the IAU Commission 3 (Astronomical Notations), in Délimitation scientifique des constellations (Delporte, 1930). (He expanded on Benjamin Gould’s boundaries for the southern constellations.)
Delporte drew the boundaries along vertical and horizontal lines of right ascension and declination; however, he did so for the epoch B1875.0, which means that due to precession of the equinoxes, the borders on a modern star map (e.g., for epoch J2000) are already somewhat skewed and no longer perfectly vertical or horizontal.

[geoffrey.landis]

This is a nice image-- very evocative; great use of color.
I'm curious, though-- what's the light source for the sky?

[Chris Peterson]

This is a nice image-- very evocative; great use of color.
I'm curious, though-- what's the light source for the sky?

Without more details we can't know whether there was a bit of Moon in the sky. But even without that, the stars themselves raise the sky background, and the upper atmosphere fluoresces as it releases energy absorbed from the Sun during the day. The darkest night skies we have on Earth are still quite bright.

[Chris Peterson]

Nice Dipper, although some of the stars, for example Alkaid, look a little bit elongated.

Compared with good astronomical telescopes, even the very best camera lenses are very poor optical systems. And nothing is more brutal in demonstrating this than bright point sources- stars. (And maybe throw in a touch of field rotation, as well, in an exposure that might have lasted 30 seconds or more.)

[Thomas Albert Miller]

More Cats Please

[geoffrey.landis]

The moon would have been my first thought, but since we're looking pretty much north, it was hard for me to think the moon could be behind the mountain. Could be-- I suppose I could fire up a planetarium program and check.

[Ann]

More Cats Please

Click to view full size image

I think, although I'm not sure, that this is Mizar the cat.

Ann

[MarkBour]

This is a nice image-- very evocative; great use of color.
I'm curious, though-- what's the light source for the sky?

The view is to the northwest, and the photographer did give one hint that it was shot in the early evening. My guess, therefore, is that perhaps the Sun is not very far below the horizon so that it gave a little light to some thin clouds, which in a long exposure, might be rather diffuse.

[neufer]

This is a nice image-- very evocative; great use of color.
I'm curious, though-- what's the light source for the sky?

The view is to the northwest, and the photographer did give one hint that it was shot in the early evening. My guess, therefore, is that perhaps the Sun is not very far below the horizon so that it gave a little light to some thin clouds, which in a long exposure, might be rather diffuse.

• 1) Yes: Pyramid Mountain is northwest of Pyramid Lake.
  
  2) It is winter time when the Sun sets in the southwest in the early evening.
  ...but the Fullmoon sets in the northwest in the late morning.

[MarkBour]

This is a nice image-- very evocative; great use of color.
I'm curious, though-- what's the light source for the sky?

The view is to the northwest, and the photographer did give one hint that it was shot in the early evening. My guess, therefore, is that perhaps the Sun is not very far below the horizon so that it gave a little light to some thin clouds, which in a long exposure, might be rather diffuse.

• 1) Yes: Pyramid Mountain is northwest of Pyramid Lake.
  
  2) It is winter time when the Sun sets in the southwest in the early evening.
  ...but the Fullmoon sets in the northwest in the late morning.

Ah, good point. So the Sun could not have dropped directly behind the mountains in that direction. Here is a quote from the photographer on his facebook page:

"Northern Exposure"
The stars of the Big Dipper -- Alkaid, Alcor/Mizar, Alioth, Megrez, Phecda, Merak and Dubhe -- are shrouded in light cirrus clouds over Pyramid Mountain in Jasper National Park. The bridge to Pyramid Island is covered in an icy frost showing the wheel tracks imprinted from a baby carriage as mom and dad paid an early evening visit to the lake.

Looking at an online planetarium tool (https://theskylive.com/planetarium) for that location and 5pm 11/7/17, the Sun would have just gone down about 60 degrees to the left of the view along that bridge. The dipper as shown by the tool matches up. Anyway, he says they are cirrus clouds. What lights them, though? I'd still think it is sunlight, it's just not emanating from behind that peak.

[neufer]

Here is a quote from the photographer on his facebook page:

The stars of the Big Dipper -- Alkaid, Alcor/Mizar, Alioth, Megrez, Phecda, Merak and Dubhe -- are shrouded in light cirrus clouds over Pyramid Mountain in Jasper National Park. The bridge to Pyramid Island is covered in an icy frost showing the wheel tracks imprinted from a baby carriage as mom and dad paid an early evening visit to the lake.

Looking at an online planetarium tool (https://theskylive.com/planetarium) for that location and 5pm 11/7/17, the Sun would have just gone down about 60 degrees to the left of the view along that bridge. The dipper as shown by the tool matches up. Anyway, he says they are cirrus clouds. What lights them, though? I'd still think it is sunlight, it's just not emanating from behind that peak.

• Indeed: it's emanating from in front of that peak:

<<Located near Jasper are Pyramid Lake and Patricia Lake. The Jasper Skytram, which takes visitors to The Whistlers' summit, and the Marmot Basin ski resort are located near the town, as is the Fairmont Jasper Park Lodge.

[MarkBour]

• Indeed: it's emanating from in front of that peak:

<<Located near Jasper are Pyramid Lake and Patricia Lake. The Jasper Skytram, which takes visitors to The Whistlers' summit, and the Marmot Basin ski resort are located near the town, as is the Fairmont Jasper Park Lodge.

The town of Jasper, the Skytram, the ski area, and the lodge you mention are all behind and to the left of the photographer (almost due south) . Jasper is about 6 km away, the other items are a little farther. Are you saying the light on the clouds came mainly from there and reflected back to the photographer's lens? That seems possible. For my theory, there is the question of why none of the clouds were pink. The photographer himself has not weighed in on the issue, where I asked on his facebook page.

[neufer]

• Indeed: it's emanating from in front of that peak:

<<Located near Jasper are Pyramid Lake and Patricia Lake. The Jasper Skytram, which takes visitors to The Whistlers' summit, and the Marmot Basin ski resort are located near the town, as is the Fairmont Jasper Park Lodge.

The town of Jasper, the Skytram, the ski area, and the lodge you mention are all behind and to the left of the photographer (almost due south) . Jasper is about 6 km away, the other items are a little farther. Are you saying the light on the clouds came mainly from there and reflected back to the photographer's lens? That seems possible.

I wouldn't rule out moonlight in front of the peak as well.

[MarkBour]

• Indeed: it's emanating from in front of that peak:

The town of Jasper, the Skytram, the ski area, and the lodge you mention are all behind and to the left of the photographer (almost due south) . Jasper is about 6 km away, the other items are a little farther. Are you saying the light on the clouds came mainly from there and reflected back to the photographer's lens? That seems possible.

I wouldn't rule out moonlight in front of the peak as well.

I wouldn't rule it out, either. But if I have the right date, the Moon would have been waning past full and not have arisen until 9 or 10 pm, by which time the Dipper would have rotated somewhat from where it appears. Actually, this would be news to me, that a bright moon can significantly illuminate clouds clear on the opposite side of the sky. Not surprising, just something new I've not observed (as is often the case in this forum).

[Chris Peterson]

The town of Jasper, the Skytram, the ski area, and the lodge you mention are all behind and to the left of the photographer (almost due south) . Jasper is about 6 km away, the other items are a little farther. Are you saying the light on the clouds came mainly from there and reflected back to the photographer's lens? That seems possible.

I wouldn't rule out moonlight in front of the peak as well.

I wouldn't rule it out, either. But if I have the right date, the Moon would have been waning past full and not have arisen until 9 or 10 pm, by which time the Dipper would have rotated somewhat from where it appears. Actually, this would be news to me, that a bright moon can significantly illuminate clouds clear on the opposite side of the sky. Not surprising, just something new I've not observed (as is often the case in this forum).

Observed how? Visually? Because an image like this is capturing much more than the eyes will ever see. A fine crescent moon, even a planet like Venus can illuminate clouds 180° away in a 30-second or 1-minute exposure.

[MarkBour]

I wouldn't rule out moonlight in front of the peak as well.

I wouldn't rule it out, either. But if I have the right date, the Moon would have been waning past full and not have arisen until 9 or 10 pm, by which time the Dipper would have rotated somewhat from where it appears. Actually, this would be news to me, that a bright moon can significantly illuminate clouds clear on the opposite side of the sky. Not surprising, just something new I've not observed (as is often the case in this forum).

Observed how? Visually? Because an image like this is capturing much more than the eyes will ever see. A fine crescent moon, even a planet like Venus can illuminate clouds 180° away in a 30-second or 1-minute exposure.

Ah. Yes, visually. My total lack of experience with long exposures with any sort of equipment shows in this illuminating discussion.