Starship Asterisk*

paulobao wrote: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!

stephen63 wrote:I wonder why ionized hydrogen isn't normally labeled the same way. HII is the same animal as Ha, right?

Chris Peterson wrote:

MargaritaMc wrote: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)

Chris Peterson wrote:

MargaritaMc wrote: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.

MargaritaMc wrote: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. :?:

MargaritaMc wrote: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.

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

APOD Robot wrote: IC 1805: The Heart Nebula

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

http://en.wikipedia.org/wiki/Cassiopeia_%28mythology%29 wrote:
<<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.>>