APOD: IC 1805: The Heart Nebula (2013 Mar 04)

[APOD Robot]

IC 1805: The Heart Nebula

Explanation: Sprawling across almost 200 light-years, emission nebula IC 1805 is a mix of glowing interstellar gas and dark dust clouds. Derived from its Valentine's-Day-approved shape, its nickname is the Heart Nebula. About 7,500 light-years away in the Perseus spiral arm of our galaxy, stars were born in IC 1805. In fact, near the cosmic heart's center are the massive hot stars of a newborn star cluster also known as Melotte 15, about 1.5 million years young. A little ironically, the Heart Nebula is located in the constellation of the mythical Queen of Aethiopia (Cassiopeia). This deep view of the region around the Heart Nebula spans about two degrees on the sky or about four times the diameter of the Full Moon.

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[neufer]

IC 1805: The Heart Nebula

A little ironically, the Heart Nebula is located in the constellation of the mythical Queen of Aethiopia (Cassiopeia).

Since, however, The Heart Nebula is located in the Perseus Arm of the Galaxy (in the constellation Cassiopeia) one can only assume that Perseus wore his own heart on his sleeve.

<<The Queen Cassiopeia, wife of king Cepheus of Æthiopia, was beautiful but also arrogant and vain; these latter two characteristics led to her downfall. Her name in Greek is Κασσιόπη, Kassiope, which means "she whose words excel". The boast of Cassiopeia was that both she and her daughter Andromeda were more beautiful than all the Nereids, the nymph-daughters of the sea god Nereus. This brought the wrath of Poseidon, ruling god of the sea, upon the kingdom of Ethiopia.

Accounts differ as to whether Poseidon decided to flood the whole country or direct the sea monster Cetus to destroy it. In either case, trying to save their kingdom, Cepheus and Cassiopeia consulted a wise oracle, who told them that the only way to appease the sea gods was to sacrifice their daughter. Accordingly, Andromeda was chained to a rock at the sea's edge and left there to helplessly await her fate at the hands of Cetus. But the hero Perseus arrived in time, saved Andromeda, killed Cetus, and ultimately became her husband.

Since Poseidon thought that Cassiopeia should not escape punishment, he placed her in the heavens tied to a chair in such a position that, as she circles the celestial pole in her throne, she is upside-down half the time. The constellation resembles the chair that originally represented an instrument of torture. Cassiopeia is not always represented tied to the chair in torment, in some later drawings she is holding a mirror, symbol of her vanity.>>

Art ("he whose words excel") Neuendorffer

[MargaritaMc]

Terry Hancock's cat helping him to make today's Apod

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http://www.flickr.com/photos/terryhancock/

About today's Apod Terry Hancock says,

Shot over 3 nights using the TMB92SS/QHY9M , this is a Hubble Palette (HST) version with SII filter assigned to Red, H-Alpha filter assigned to Green and OIII filter assigned to blue channel.
Total Exposure 14.5 hours
Image Information
Location: DownUnder Observatory, Fremont MI
Date of Shoot August 29th,30th and 31st 2012
Exposures:
QHY9M mono CCD
H-Alpha 3nm 11 x 30 min
OIII 8.5 nm 8 x 30 min
SII 8 nm 10 x 30 min

I'm getting to grips with astrophotography (theory, not practice...) and would be helped if some kind soul would clarify what the figures of nanometres mean in the above quote, in the description of the filters used. Many thanks,

Margarita

[Chris Peterson]

About today's Apod he says,

Shot over 3 nights using the TMB92SS/QHY9M , this is a Hubble Palette (HST) version with SII filter assigned to Red, H-Alpha filter assigned to Green and OIII filter assigned to blue channel.
Total Exposure 14.5 hours
Image Information
Location: DownUnder Observatory, Fremont MI
Date of Shoot August 29th,30th and 31st 2012
Exposures:
QHY9M mono CCD
H-Alpha 3nm 11 x 30 min
OIII 8.5 nm 8 x 30 min
SII 8 nm 10 x 30 min

I'm getting to grips with astrophotography (theory, not practice...) and would be helped if some kind soul would clarify what the figures of nanometres mean in the above quote, in the description of the filters used.

The filters used are bandpass filters, meaning they allow a range of wavelengths through, excluding longer and shorter wavelengths. Bandpass filters are specified by two key values: the center wavelength, and the bandpass (the width of the filter). The narrower the filter, the less off-band light it passes.

Any H-alpha filter is centered on 656 nm. The filter used here was very narrow, only 3 nm wide, meaning it passes light from 654.5 nm to 657.5 nm. The OIII and SII filters are a little wider, being about ±4 nm around their center wavelengths. So, more specifically, the filters are:

H-a 656.28 ± 1.5 nm
OIII 500.7 ± 4.25 nm (or more likely, centered between the 500.7 nm and 495.9 nm doublet)
SII 671.7 ± 4 nm (or more likely, centered between the 671.7 nm and 673.1 nm doublet)

[MargaritaMc]

Got it! Thank you very much, Chris.
Margarita

PS - I am wondering why doubly ionised oxygen is known as 0111 and not 011? And the same with singly ionised sulfur being called S11.

[Chris Peterson]

Got it! Thank you very much, Chris.
Margarita

PS - I am wondering why doubly ionised oxygen is known as 0111 and not 011? And the same with singly ionised sulfur being called S11. :?:

Those should be Roman numeral ones ( "I") not Arabic numerals.

OI is neutral oxygen, OII is singly ionized, OIII is doubly ionized, and so on.

[stephen63]

I wonder why ionized hydrogen isn't normally labeled the same way. HII is the same animal as Ha, right?

[MargaritaMc]

Got it! Thank you very much, Chris.
Margarita

PS - I am wondering why doubly ionised oxygen is known as 0111 and not 011? And the same with singly ionised sulfur being called S11.

Those should be Roman numeral ones ( "I") not Arabic numerals.

Thank you

OI is neutral oxygen, OII is singly ionized, OIII is doubly ionized, and so on.

And thank you, AGAIN!

M

[paulobao]

About today's Apod he says,

Shot over 3 nights using the TMB92SS/QHY9M , this is a Hubble Palette (HST) version with SII filter assigned to Red, H-Alpha filter assigned to Green and OIII filter assigned to blue channel.
Total Exposure 14.5 hours
Image Information
Location: DownUnder Observatory, Fremont MI
Date of Shoot August 29th,30th and 31st 2012
Exposures:
QHY9M mono CCD
H-Alpha 3nm 11 x 30 min
OIII 8.5 nm 8 x 30 min
SII 8 nm 10 x 30 min

I'm getting to grips with astrophotography (theory, not practice...) and would be helped if some kind soul would clarify what the figures of nanometres mean in the above quote, in the description of the filters used.

The filters used are bandpass filters, meaning they allow a range of wavelengths through, excluding longer and shorter wavelengths. Bandpass filters are specified by two key values: the center wavelength, and the bandpass (the width of the filter). The narrower the filter, the less off-band light it passes.

Any H-alpha filter is centered on 656 nm. The filter used here was very narrow, only 3 nm wide, meaning it passes light from 654.5 nm to 657.5 nm. The OIII and SII filters are a little wider, being about ±4 nm around their center wavelengths. So, more specifically, the filters are:

H-a 656.28 ± 1.5 nm
OIII 500.7 ± 4.25 nm (or more likely, centered between the 500.7 nm and 495.9 nm doublet)
SII 671.7 ± 4 nm (or more likely, centered between the 671.7 nm and 673.1 nm doublet)

Not so...
An Ha 3nm filter is an optical filter designed to transmit a narrow bandwidth of light centered on the H-alpha wavelength (656.3nm) ± 3nm. It means that the filter will reject any other wavelength except the Ha wavelength ± 3nm. That said a 3nm ha filter will let pass the wavelength from 653 to 659nm! (but this is a teoretical value...I measured mine!).
The same for the other filters!

Cheers,
paulo

[Chris Peterson]

I wonder why ionized hydrogen isn't normally labeled the same way. HII is the same animal as Ha, right?

We need to distinguish between an ionized atom and a spectral line. Although the terms are often used synonymously, they are different things. When you ionize a gas, there are usually many possible electron transitions, each of which produces a photon with a distinct wavelength. H-alpha is one specific emission line (n=3 to n=2) that can be produced by ionized hydrogen.

The filters used to isolate emissions from various ionized gases are tuned to single lines or doublets, usually the brightest, produced by those atoms. But there are other lines as well, and sometimes specialized projects look at those instead. Hydrogen (which can only be singly ionized, of course) was the first atom that had its emission spectrum closely studied, a legacy seen in the specific names associated with it- the Lyman series, Balmer series, and specially named lines, like H-alpha. HII regions in space are typically mapped using H-alpha emissions, but sometimes H-beta or other lines.

[Chris Peterson]

An Ha 3nm filter is an optical filter designed to transmit a narrow bandwidth of light centered on the H-alpha wavelength (656.3nm) ± 3nm. It means that the filter will reject any other wavelength except the Ha wavelength ± 3nm. That said a 3nm ha filter will let pass the wavelength from 653 to 659nm! (but this is a teoretical value...I measured mine!).
The same for the other filters!

What kind of filters do you use? If yours are specified that way, it is unusual. The conventional specification for bandpass width is the full width at half maximum for the filter, not a plus/minus value. A 3 nm H-alpha filter will be centered on 656.3 nm, and will have a FWHM of 3 nm. The higher quality the filter, the steeper the cutoffs will be, with an ideal filter (which doesn't exist) acting like a notch, with the same width from top to bottom. The narrowest standard astronomical interference filters I know of are made by Astrodon. Below is the typical bandpass for their 3 nm filter, which also follows the convention of defining width by the bandpass at half maximum. While it would be perfectly acceptable to describe a filter with its center and a plus/minus range, seeing just a single value for range should be interpreted as the FWHM bandpass.

[paulobao]

Hi,

I use Astrodon NB filters! And you are right, sorry! I allways thougth it was center wl ± x nm, but after reading the Astrodon specifications I see it's not!

Regards,
paulo