Starship Asterisk*

But, Ann, do the narrow bands of ionisation wavelengths relate to temperature in the same way as starlight? I think they rather relate to the elements being ionised.

The difference is that IC 435 is a "pure" reflection nebula, centered on B5V-type star HD 38087, which is too cool to ionize an emission nebula. IC 432, by contrast, is centered on B2IV star HD 37776, which is just hot enough to ionize a faint emission nebula . But HD 37776 is not hot and...

I suppose if one is north of latitude +45 degrees on Earth, it might be hard to view the southern most extremes of the scorpion's tail, especially without a clear southern horizon. But otherwise, I'd say Scorpius contains one of the more prominent asterisms crossing the ecliptic. I imagine many Amer...

I am guessing that the colours we see in the APOD are vaguely similar to those of a "true colour" visible light image, as the progression from blue to red still indicates decreasing temperatures. But the relative magnitudes might be quite different from a visible light image. Correct?

Got up very early this Sunday morning, for an early season peek at Saturn, about three months prior to its opposition and just a few days prior to its western quadrature with us. (Had there been less clouds, and had I been more awake, I might have captured Jupiter, Venus and Mercury, too.) Saturn is...

Very sharp. On Mr Addis' instagram site, he says he was holding the scope and manually tracking with aid of his finderscope. I own the same make and model of scope, and have never attempted hand held photography with it and certainly not when tracking. Respect. Lucky imaging indeed. I also have the ...

Hmm. Try: https://www2.lpod.org

The "wide spectrum" filters used were, I think, the F275W (B), F336W (G) and F438W (R) shown in this graph: http://www.stsci.edu/hst/wfc3/ins_performance/UVIS_sensitivity/UVIS_Wide1.jpg http://www.stsci.edu/hst/wfc3/ins_performance/UVIS_sensitivity/UVIS_Wide1.jpg I read this as the visible...

My bad. The nebula is, of course, IC 432. Forget everything I said about IC 435. Ann Don't be too hard on yourself, Ann, they are just funny coloured puffs of almost nothing, after all. I was also unsure which was which when I was writing my earlier posts, so I only referred to the image colours in...

Lunar Photo Of the Day: lpod.org

What I don't understand about today's APOD is the blue mapping of the reddest channel. But maybe that was for aesthetic reasons, or in order to map Hα as red and OIII as green. Ann The APOD is just "RGB=HOS", rather than the "RGB=SHO" that is perhaps more commonly seen in narrow...

What I am less sure about is the reasoning behind the different exposure times for each channel. If I attempt to account for the 2x2 binning in the G and B channels, it looks like the effective ratios from each channel are about R=10%, G=60%, B=30%. I am sure there must be a reason to do this, but ...

The red/orange/brown/yellow shades in the APOD are showing the dominance of the red channel (Ha ~656nm [red]) and green channel (OIII ~500nm [cyan-green]), with a relative lack of signal in the blue channel (SII ~672nm [the reddest wavelengths recorded]). The yellow shades are where the the signal f...

But it is one of the best approximations to what our eyes might see, if they were more sensitive and had narrowband filters. If ifs and buts were sweets and nuts, we'd all have a merry solstice.

I'm not even sure you need to be a citizen.

Thank you for all the details, David.

Guest wrote: ↑Mon Apr 01, 2019 9:26 am I'm wondering if today's Earth Science Picture of the Day is also an April Fools joke?

Check it out! https://epod.usra.edu/blog/

I'm wondering if your wondering is another one.

I don't think it would require a much bigger animation to give a good rough impression of all the periods. The problem is doing it as a GIF. Not very efficient for that type of animation. I should have said I don't think it would require many more frames, regardless of format. But I don't think it ...

I don't think it would require a much bigger animation to give a good rough impression of all the periods.

I would assume that Gaia recorded enough samples from each RR Lyrae star, to determine the average period of each. So, I suppose they could have produced a more realistic gif, but for what purpose, I don't know. An ordinary luminosity vs time graph, for each variable star, would convey that more cle...

Mark,

Stellarium is free software, and can be used in much the same way as Ann described her use of Guide.

This is what it looks like:

The HST image of Arp 194, recorded in Jan 2009, must have been one of the last to be recorded with the WFPC2 camera, which was removed in May 2009, and replaced with the WFC3 camera. The 2002 paper than Ann provided a link to, and the 2016 paper in the "because of" link in the APOD caption...

The initial error (by whoever) of locating Arp 194 in Cepheus was fairly minor. That it has been copy-pasted so many times, on so many different sites (more sites than listed by Art and bystander), over a decade, with no verification, is a bit poor.

Chris, that sounds like typical teenage behaviour in the 70s ... abusing alcohol and messing around with psychedelics like CCD, to make the stars look pixelated.

No Bruce, but I'm almost certain that I did.