by Ann » Mon Feb 20, 2023 6:31 am
The picture that is today's APOD is seen at left in the double portrait above. According to NASA, two filters were used for the image, one visible one and one near-infrared one. I'll have a guess and say that the visible one was probably centered at 656 nm, the wavelength of hydrogen alpha, whereas the near-infrared one was almost certainly Hubble's trusted 814 nm filter. And the red hydrogen alpha nebula surrounding the cluster was mapped as blue, and the mostly blue stars, detected by an infrared filter, were shown as yellow. I must say that the colors bother me.
The picture at right, constructed from two ultraviolet, two visible and one near infrared filter, gives a much "truer" portrait of NGC 1850. This young globular cluster (well, maybe Chris would call it a "populous cluster") is apparently only about 100 million years old, the same age as the Pleiades.We do expect to find a lot of at least moderately bright blue stars in such a cluster. And in a 100 million year-old cluster as large as NGC 1850, we do expect to find a lot of rd giant stars as well.
I will not say that Hubble's five filter portrait of NGC 1850 shows the cluster in "true color", since three of the five filters detect wavelengths that are not visible to the human eye. But the five filter portrait is still so much better than the two filter one.
Here is another version of NGC 1850, processad by our very own Judy Schmidt, Geckzilla, from Hubble data:
The stars are not blue, but this is almost certainly due to dust reddening. At least the stars aren't as uniformly yellow as they are in the APOD. And the nebulosity is red, as it should be.
Go to
this page to read Geck's comment and to see the full size of the image.
Ann
[img3="NGC 1850 as seen through two filters (left) and through five filters (right)."]https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/thumbnails/image/ngc1850_2versions-02.jpg[/img3]
The picture that is today's APOD is seen at left in the double portrait above. According to NASA, two filters were used for the image, one visible one and one near-infrared one. I'll have a guess and say that the visible one was probably centered at 656 nm, the wavelength of hydrogen alpha, whereas the near-infrared one was almost certainly Hubble's trusted 814 nm filter. And the red hydrogen alpha nebula surrounding the cluster was mapped as blue, and the mostly blue stars, detected by an infrared filter, were shown as yellow. I must say that the colors bother me.
The picture at right, constructed from two ultraviolet, two visible and one near infrared filter, gives a much "truer" portrait of NGC 1850. This young globular cluster (well, maybe Chris would call it a "populous cluster") is apparently only about 100 million years old, the same age as the Pleiades.We do expect to find a lot of at least moderately bright blue stars in such a cluster. And in a 100 million year-old cluster as large as NGC 1850, we do expect to find a lot of rd giant stars as well.
I will not say that Hubble's five filter portrait of NGC 1850 shows the cluster in "true color", since three of the five filters detect wavelengths that are not visible to the human eye. But the five filter portrait is still so much better than the two filter one.
Here is another version of NGC 1850, processad by our very own Judy Schmidt, Geckzilla, from Hubble data:
[img3=""]https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/Globular-like_NGC_1850.png/400px-Globular-like_NGC_1850.png[/img3]
The stars are not blue, but this is almost certainly due to dust reddening. At least the stars aren't as uniformly yellow as they are in the APOD. And the nebulosity is red, as it should be.
Go to [url=https://commons.wikimedia.org/wiki/File:Globular-like_NGC_1850.png]this page[/url] to read Geck's comment and to see the full size of the image.
Ann