Hickson’s from Sweden

[Hakann]

I plan ing to observe the Hickson series here from Sweden at 62 degree in a 30” scope.
Last spring Hickson 50 had a good position and a clear night at zenith I could say I saw easy 3 components ( but I lower it to 2 components )
Place is not the best but it was SQM-21.5 ) and a clear night ( zenith is Ok ) but last fall I was at M33 low position to Stockholm direction and I could barley se the galaxy ( around same darkness )
Example, one night at OSP I was in Chucks 25” and the arms and detail on M33 was a killer, and if memory is correct it was SQM-21.90.

So here I need a good position for haunt the Hickson's.

Last spring I also had a great view at Stephan’s ( as a member in Hickson ) and it was great even if it was not direct up at zenith.
- I has been on them before in clubs 18” and many time on LaPalma in 16,20,25” scops and not that easy - but in the 30” it was awesome.

So any idea what group might be best here in September ( Uppsala/Sweden ) straight up.

[Clear Skies]

This is Uppsala, Sweden at midnight 15 September.

hickson.jpg

[Hakann]

What is the best object as far up at possible from say 9 to 3 at the peak after midninght.
I rather want be lower than 75 degree.

[Hakann]

I obseved HCK 1 and 82 and saw all 4 galaxys in the 30” f/3/6 and sky was around SQM-21.25 and observings was not towards Stockholm ( + 1 milion people and more in that area )
I used ethos 8 mm and PII.
Me, I had never see a gain on use ex DeLite from Ethos and remove the Paracorr.
Guess area where I’m is to bright.
Beside, I also enjoy wide fields at even 400X.
EP that has 20 mm ER is hard on my eyes, and 15 mm is a no issue.

Question ; What is the best mag to use on Hickson groups if you has a idea.
Guess thats is on aperture and sky, but anyway.

Rain is here so this weekend was off, so now Oktober for more HCK’s.

[wvreeven]

Here when I write "object" I mean an extended object like a nebula or galaxy. The case of stars is fascinating as well but largely different from the case of extended objects.

Our eyes work in a funny way. They need contrast (which is defined as the surface brightness of the object divided by the surface brightness of the background) and intensity (which in this context doesn't mean total brightness of the object but it really means surface brightness) to see things. The more you magnify, the more the (apparent) surface brightness drops. Note that the contract does not drop with increasing magnitude since the surface brightness of the object and the surface brightness of the background decrease with the same factor. The intensity drops since the surface brightness drops and at some point the intensity becomes so low that our eyes don't register it anymore.

But when BOTH the surface brightness becomes low AND intensity drops, our eyes need objects to be LARGER to see them. So, increasing the magnification helps to see fainter objects! That sounds very much like a contradiction of course but it is true. The optimum (apparent) angle for our eyes to see faint objects is around 3º so in order to see a, say, 1 arc minute wide galaxy a magnification of 3 x 60 (because there are 60 arc minutes in a degree) = 180x is needed. At that magnification the outer areas of the galaxy may have dropped beyond the detection intensity of our eyes so you should magnify even more to see the galaxy well which makes more outer areas disappear etc. Either at some point you see the galaxy or it becomes so faint that it drops beyond your vision.

So, yes, it depends on aperture and sky but more on the sky! In a dark sky the contrast is much higher which makes it easier to see faint extended objects since the contrast will be higher. That allows for higher magnifications. A large aperture collects more light but, contrary to what many people believe, DOES NOT INCREASE CONTRAST!!! Both the object and the background profit of exactly the same amount of the larger aperture and the contrast between a galaxy and the background is EXACTLY the same in a 24" telescope or a 4" telescope (or even the naked eye) irrespective of magnification! The ONLY way to make objects better visible is by making the sky background darker. For galaxies this means going to areas with little or no light pollution.

The fact that an object is visible in a telescope and for instance not with the naked eye is mostly because of the magnification that a telescope offers though the light collecting capabilities of the telescope help as well of course which is why small objects are much easier to see in a large telescope then a small one. If you use a telescope at a magnification that yields an exit pupil the size of your eye pupils then the sky background (and therefore the object as well) will have the same surface brightness as with the naked eye. If you then see an object that is invisible with the naked eye, the ONLY reason why you see it is the magnification (which you can apply due more light having been collected by the telescope). If you then increase magnification, the surface brightnesses of both the background and the object will drop with the same factor and we're back at what I explained before.

If you observe an object with a 4" and with a 24" telescope at magnifications that yield an exit pupil equal to the pupil of your eye, then the magnification in the 24" will be 6 times as high as in the 4". If you observe the object in both telescope at the same magnification and that magnification yields an exit pupil equal to the pupil of you eye, then the surface brightnesses of the background and the object will be 36x as low in the 4" as in the 24" which is why we use big telescopes.

As for the best magnification to observe Hickson groups: that depends on whether you want to see the group as a whole or the individual galaxies. If a Hickson group is 30 arc minutes across and each galaxy is 1 arc minute across then a magnification of 6x is needed for the Hickson group and 180x for the individual galaxies. But in practice I usually apply magnifications of 300 to 700x to observe galaxies and the higher magnifications only if the seeing allows.

My apologies if this story is too long and not very coherent. It literally is a brain dump

[Hakann]

LaSerena, Nice.
I was going to Vicuna/Pangea 2019 but decided OSP and LaPalma again, and after that travell has been hard.

You has another sky than me here at 62 degree, so summer is off and winter is tuff to obseve at as in many ways ( not just the cold )

Sky here for most DS objects depending on aperture stops around 200X, but some objects one can push more even if the sky really not allowe it at 4-500X.

I has notice some objects as galaxy’s become more easy to see in lower mag.
The place I had my 30” at is not a great place ( as decribed ) but as been before to LaPalma 6 years in a row I know even there it’s hard to visual observe as light pollution ( small iland ) and sky can be dark but calima, hight alt can be cold/windy and seeing on west ( dry side at 700 m ) can be in turbulance ( seeing issues ) but overall it’s way better than Sweden of course.
Now I can’t say on the sky other time of year than December but owner of Athos Astronomy told me it’s not really a ’best’ time of year.

I been to south Sahara in April but not as good as expected.
I also been to Oz Sky/Australia ( did love southern sky ) and decent darkness but allot of dew.

I’ll been to Austria alps ( hight alt ) but it was dew/foggy )
OSP 5 years has been Ok but the fire has been the issue in August.

One of the best telescope I ever been used was a 25” Lomo f/4.5 ( thick plano in Sitall ) and owner made it less a coma corrector and used Ethos EP ( mid or higher power only )
I’ll just loved that scope and he wanted 27K Euros for it ( optics was 35K Euros 10 years ago ) but at that time I did not care for a f/4.5, but heard it was sold for 16K Euros ( what a shame )

I has not been to Texas on obesvings, but a night in Jim’s 48” would be nice.

I still one one day come to Chile.

[akarsh]

Hi Hakann

If you haven't looked at the Hickson observing guide created by fellow DSF member Reiner Vogel, it's a great resource for anyone pursuing the Hicksons: http://www.reinervogel.net/pdf/Hickson.pdf

Alvin Huey also has an observing guide, which I do not yet own: http://www.faintfuzzies.com/HicksonGuide2.html

I have observed 44 of the Hickson groups, mostly with my 18" f/4.5, but maybe 4--5 of them are from Jimi's 48". Hickson 50 is widely regarded as the most difficult Hickson group. So seeing just a few galaxies with a 30" is okay. With most Hickson groups in my 18", I can usually see 60--70% of the members, but for some (like HCG 50, HCG 17), it is much harder. Also for some groups like HCG 55, I can only sense a clump but not resolve it.

I agree with what Wouter says with regards to magnification and the role of dark skies. Generally, there's a thumb rule quoted by lots of people on CloudyNights etc. that says the you must use an eyepiece which has about 2mm of exit pupil. I have usually found this to be "too much" exit pupil. On my 18" f/4.5, 2mm exit pupil corresponds to about 200x magnification. I usually get much better results between 375x (6mm Delos) and 450x (4.5mm Delos).

One more factor which I think is important is seeing. The role of seeing here is that poor seeing will blur your galaxies out and render them to have lower surface brightness than they actually have. So when you're looking at tiny galaxies, like many of the Hickson cluster members, you will also benefit greatly from having steady seeing.

To find which galaxies are well-placed for a given night, the way I usually check is to look up the Local Sidereal Time (LST) at your typical observing time. I use an iPhone app called LSTClock (I think it's free) or you can also find web-based calculators like this one: http://www.jgiesen.de/astro/astroJS/siderealClock/
An object is best positioned (transiting) when the RA = LST, so you should try to observe objects as close as possible to this condition. If you go through any atlas of Hickson objects, they will have RA listed. For example, the LST at Uppsala during midnight nowadays is about 23:30 very roughly, so this means about RA of 22:00 will be well-placed before midnight. But objects of a southern declination will gain airmass very quickly, so you should observe them as close to RA = LST as possible. For more northern things, you could say maybe ±2 hours either way is okay.

Here's a list of all Hicksons that are well-placed before midnight. Pay attention to the southern objects to match LST as closely (± 20 min should be okay) as possible.

HCG #	RA (J2000)	Dec (J2000)
88	20:52:22.8	-05:45:28
89	21:20:10.8	-03:54:32
90	22:02:05.6	-31:58:0
91	22:09:12.4	-27:46:33
92	22:36:00.5	+33:57:57
93	23:15:24.2	+18:58:59
94	23:17:16.5	+18:43:11
95	23:19:31.8	+09:29:31
96	23:27:58.3	+08:46:27
97	23:47:26.9	-02:18:20
98	23:54:12.8	+00:22:24
99	00:00:43.7	+28:23:20
100	00:01:18.0	+13:07:00

(Small caveat in the above explanations -- we should be using the precessed RA rather than J2000 to compare to LST, but right now this is a minor detail.)

Clear Skies

Regards
Akarsh