by Ann » Sun Jul 28, 2019 7:30 pm
BDanielMayfield wrote: ↑Sun Jul 28, 2019 2:11 pm
I get that the clouds would look so different, but what I find surprising is that you see what to me looks like two almost completely different sets of stars. It's as if visible light and infrared light stars are each invisible in the other light range. And yet the visible and IR bands are side by side in the EM spectrum!
Bruce
Visible and infrared images do indeed often look completely different. For example, we are used to seeing the "dark divide" between the North America Nebula and the Pelican Nebula as "empty"; but the infrared Spitzer image shows that these parts of the North America Nebula region are generally the most active ones in star formation and the most brilliantly lit up in infrared light.
Another thing to bear in mind is that cool red stars look bright and often blue in infrared images, whereas hot blue stars look tiny and faint. For example, look at the Spitzer image of the APOD and note a relatively bright blue star at upper left. Well, this star is an M-type giant, cool and bright in infrared light, although rather unimpressive in visible light. The star is HD 199799, and its bright near infrared light makes the star shine brightly blue in the Spitzer infrared image. By contrast, the relatively bright blue star at top center in the visible image, O-type star HD 199579, is so faint in infrared light that I suggest that you put your fingernail over the star on the visible light screen in order to find it when you move your cursor over the image to see the infrared image. Because that tiny blue ember that is all that remains of the hot bright star when we see it in infrared light.
Similarly, the really bright blue "eye" of the Pelican Nebula at center right, B-type star HD 199081, disappears almost completely in the Spitzer image.
Visible light Double Cluster of Perseus.
Photo: Roth Ritter.
For comparison, lets take a look at the famous Double Cluster of Perseus in both visible and infrared light. In the visible image at right, note the five red supergiants in Chi Persei, NGC 884, which stand out brilliantly in the infrared image of the Double Cluster. Note, by contrast, how faint the blue supergiants are in infrared light.
Ann
[quote=BDanielMayfield post_id=294060 time=1564323070 user_id=139536]
I get that the clouds would look so different, but what I find surprising is that you see what to me looks like two almost completely different sets of stars. It's as if visible light and infrared light stars are each invisible in the other light range. And yet the visible and IR bands are side by side in the EM spectrum!
Bruce
[/quote]
[float=left][img2]http://www.spitzer.caltech.edu/uploaded_files/graphics/fullscreen_graphics/0007/8746/ssc2011-03b_Sm.jpg[/img2][/float]Visible and infrared images do indeed often look completely different. For example, we are used to seeing the "dark divide" between the North America Nebula and the Pelican Nebula as "empty"; but the infrared Spitzer image shows that these parts of the North America Nebula region are generally the most active ones in star formation and the most brilliantly lit up in infrared light.
Another thing to bear in mind is that cool red stars look bright and often blue in infrared images, whereas hot blue stars look tiny and faint. For example, look at the Spitzer image of the APOD and note a relatively bright blue star at upper left. Well, this star is an M-type giant, cool and bright in infrared light, although rather unimpressive in visible light. The star is HD 199799, and its bright near infrared light makes the star shine brightly blue in the Spitzer infrared image. By contrast, the relatively bright blue star at top center in the visible image, O-type star HD 199579, is so faint in infrared light that I suggest that you put your fingernail over the star on the visible light screen in order to find it when you move your cursor over the image to see the infrared image. Because that tiny blue ember that is all that remains of the hot bright star when we see it in infrared light.
Similarly, the really bright blue "eye" of the Pelican Nebula at center right, B-type star HD 199081, disappears almost completely in the Spitzer image.
[float=left][img2]https://cdn.iopscience.com/images/0004-637X/796/2/127/Full/apj501837f1_lr.jpg[/img2][c][size=85]Infrared Double Cluster of Perseus.
Source: https://iopscience.iop.org/article/10.1088/0004-637X/796/2/127[/size][/c][/float] [float=right][img2]http://annesastronomynews.com/wp-content/uploads/2012/02/The-Double-Cluster-in-Perseus-by-Roth-Ritter.jpg[/img2][c][size=85]Visible light Double Cluster of Perseus.
Photo: Roth Ritter.[/size][/c][/float]
For comparison, lets take a look at the famous Double Cluster of Perseus in both visible and infrared light. In the visible image at right, note the five red supergiants in Chi Persei, NGC 884, which stand out brilliantly in the infrared image of the Double Cluster. Note, by contrast, how faint the blue supergiants are in infrared light.
Ann