Galaxy appreciation questions

[domstar]

It's spring and I've been so fortunate to be among the Virgo galaxies 3 times over the last few days. I was going to write a report but I thought I'd ask a few questions instead. 

1. Which Messier galaxy do you find most difficult in the Leo/ Virgo/ Coma Berenices area? Last night it was M 89. How can that be?

2 Magnification/ field of view / exit pupil. I've got an Aero 30mm (30x) and a starguider 25mm (36x). The starguider should give a darker background but a dimmer image. What would you choose?

3 M 91. Why isn't it marked on stellarium? There's a picture of a galaxy there but no identification and you can't click on it. If I write a search for it, it appears. Is it just me?

4 Am I the only person who has a nightmare trying to find Kappa Leo? Maybe it's the best reason to get a right angle finder.

5 Transparency/ seeing. I've had decent views of galaxies despite stars being much too fuzzy to split doubles. Does seeing impact the resolving of airy discs? It seemed that the air was too moist but galaxies were a pleasure. What am I experiencing when I have fuzzy stars but viewable galaxies?

6 Lastly, what area is your favourite view. The Leo Triplet? Markarian's Chain? Aperture will obviously be part of this. My favourite is probably M 49 and a couple of stupidly titled 'Lost Galaxies'. Found galaxies more like although I do feel a certain amount of ugly smugness at observing a so-called 'Lost' galaxy.

Anyway, despite being stuck on the balcony, it's been a privilege to be viewing one of the true wonders of the sky.

Clear skies to you all.

Dominic

 

[vlaiv]

2. There is a sweet spot in contrast region - when background goes dark enough but targets don't become too dark. It will depend on the target and level of light pollution.

It is about 2-3mm exit pupil size. Of course, eyepiece itself will play a role - how clear the glass is and how good are coatings. Number of elements plays a role sometimes too.

You really need to check what works best for you on particular target

5. Transparency and seeing are two different things.

Seeing affects point sources like stars and affects sharpness of objects - usually planetary targets and maybe globular clusters and such. Transparency is level of clearness of atmosphere - or maybe better described how hazy atmosphere is due to dust / smoke / water vapor.

Transparency impacts how visible faint extended objects are like nebulae and galaxies.

Two often come "out of phase". For example, transparency tends to be really good after rain - because rain drops pick up dust from atmosphere and make it clear. However - seeing is poor in those condition due to all the turbulence.

Another example is thermal inversion. Seeing tends to be exceptional in those conditions - but haze also tends to form - very much lowering transparency.

 

[domstar]

Thanks Vlaiv. I sort of thought that about seeing but I also feel like it's damp when the stars are fuzzy. I look at the light dome of the town and when it's higher I assume a damp atmosphere and fuzzy stars. So if I understand it then that's poor seeing.

[vlaiv]

1 minute ago, domstar said:

Thanks Vlaiv. I sort of thought that about seeing but I also feel like it's damp when the stars are fuzzy. I look at the light dome of the town and when it's higher I assume a damp atmosphere and fuzzy stars. So if I understand it then that's poor seeing.

Fuzzy is rather fuzzy term

Flickering stars mean poor seeing. Stars on threshold of detection popping in and out of view is seeing. Seeing is the same thing that happens when you look over a fire when doing a barbecue (or looking over hot road on summer say).

Halo around stars is due to water vapor - haze, but stars will usually be still in that case. It is easiest seen on the Moon. Next time there is a full moon - look at it and look at sky around it. If sky is very dark - transparency is good, but if there is halo around the moon and sky is very bright there - transparency is poor. Same thing can happen with stars (but to lesser extent).

Here is what it might look like:

Good tranparency:

Poor transparency:

[domstar]

Thanks for that. Would it be true to say that stars that don't focus down to a point are caused by moisture and issues with transparency, which would affect galaxies too but maybe to a lesser extent? Therefore, splitting doubles is unsatisfying whereas finding galaxies is still pleasurable (more fuzzy vocabulary). Bear in mind that I'm just using a 4 inch refractor so I'm not exactly tracing out the spiral arms- more like just detecting them. 

I guess what I'm trying to say is mediocre transparency means no doubles but galaxies are still on the menu albeit not at their very best. Is that how others see it?

[jetstream]

54 minutes ago, domstar said:

2 Magnification/ field of view / exit pupil. I've got an Aero 30mm (30x) and a starguider 25mm (36x). The starguider should give a darker background but a dimmer image. What would you choose?

 

43 minutes ago, vlaiv said:

It is about 2-3mm exit pupil size

In general this is a vg range, some take more some less. Last night I took one EP out for the 15"- the17.3 Delos @ 105x and 3.6mm exit pupil. More mag would have been a benefit but this works so well on M101 and M81, pulling out the fickle spirals.

Try 3mm ish exit pupil in a wide or hyperwide IMHO.

54 minutes ago, domstar said:

Does seeing impact the resolving of airy discs? It seemed that the air was too moist but galaxies were a pleasure. What am I experiencing when I have fuzzy stars but viewable galaxies?

Yes, it can- ie stars should take mag up to the limits of the scopes optical specs but don't- a great example is E and F in the trap, more mag is usually not good, there is a sweet spot. Faint galaxy cores are also seeing sensitive. Low scatter EP's are a benefit on stars.

Edited April 21, 2020 by jetstream

[vlaiv]

17 minutes ago, domstar said:

Thanks for that. Would it be true to say that stars that don't focus down to a point are caused by moisture and issues with transparency, which would affect galaxies too but maybe to a lesser extent? Therefore, splitting doubles is unsatisfying whereas finding galaxies is still pleasurable (more fuzzy vocabulary). Bear in mind that I'm just using a 4 inch refractor so I'm not exactly tracing out the spiral arms- more like just detecting them. 

I guess what I'm trying to say is mediocre transparency means no doubles but galaxies are still on the menu albeit not at their very best. Is that how others see it?

Transparency is related to letting light thru. Greater transparency - more light comes thru and worse transparency means less light. It is even worse than that simple explanation because stuff in atmosphere that block light - also scatters light, which affects how much light pollution you will see in the sky and how bad or good contrast will be.

Poor transparency means less light form the target and often means more light pollution in the sky - or higher light dome if you will.

This is unrelated to seeing. Seeing is related how turbulent atmosphere is. It affects our ability to see fine detail and prevents us to use high magnifications as image looks soft. In really poor seeing stars are difficult to focus.

Seeing can be due to atmosphere but also due to local conditions - observing over houses (particularly in winter when people heat their homes and some of that heat escapes), over bodies of water (water retains daytime heat and radiates at night), concrete and paved areas, with scopes that have not properly cooled - all of those cause what is called - "local seeing".

Sometimes weather phenomena correlates transparency and seeing - and sometimes it anti correlates them. But they are in general different phenomena. Transparency affects galaxies and faint stuff that is extended, while seeing affects sharp things - like stars and planetary detail.

[John]

On your question 2, I generally find that my 21mm eyepiece gives a more contrasty view of galaxies than my 31mm does. I have some moderate light pollution where I observe. When I want to tease out fainter targets I add more magnification, eg: 13mm or even 8 or 6mm eyepiece.

On question 6, I guess it is scanning up or down Markarians Chain. I have also had nice views of the structure within Messier 64 recently and also observing the "Siamese Twins" NGC 4567 and 4578 "interacting" was lovely.

 

[domstar]

Thanks for the tips John. I nearly caught a glimpse of the Siamese Twins last night but not quite. I had a look for them as I spent a lot of time around M 58 as I branched out from there to fainter stuff and had to start again many times.

Unfortunately, I'm confined to an obstructed balcony at the moment so M 64 will have to wait a year. Still, I've been spoilt with clear nights and decent views this April.

[jetstream]

4 hours ago, domstar said:

What would you choose?

You know, one of my favorite eyepieces is the 25mm Televue plossl, great on everything and its coming out tonight. A 20mm would be great in your scope- these high transmission,low scatter eyepieces can make a bit of a difference compared to many widefields.