Starhopping under city skies

[The60mmKid]

Greetings,

I'm moving to London in a few weeks. I'm an adept starhopper, but I'm accustomed to observing under Bortle 3-7 skies. So, I'd be grateful for suggestions on equipment and skills for urban starhopping (e.g., size/FOV/exit pupil of finderscope?). I am not interested in converting to go-to! I am considering setting up my 60mm refractor to use as a superfinder for my 5" refractor... 5.13° FOV, 4.53mm exit pupil. Good enough, or greater FOV needed due to a lack of naked-eye reference stars?

Thank you!

The Kid

[Zermelo]

Hello

I expect you will be navigating using a combination of optical finder and a widefield eyepiece in the main scope.
If you don't already have it, I'd suggest decent planetarium software (I use Skysafari):

(1) you can easily vary the magnitude depth of the view, and "tune" it to match what you're seeing in whichever instrument you're using

(2) it can show TFOV circles for the finder and any eyepiece/scope combination you care to set up. These can be used during sessions, or ahead of time to plan hops.

(3) you can easily flip up/down and left/right as you switch between finder and main scope (if that's necessary, depending on the optical properties of each)

I'm not sure about the value of unit finders in those conditions. I'm lucky enough to have Bortle 4, so there's normally plenty to go at, but when the moon is full my Telrad isn't too great.

There is this book, which is mostly about the objects you can find, even in polluted skies, but does also include some general discussion about techniques and equipment for urban settings. If you are experienced already, though, it probably won't have much to surprise you on that score.

City-based members may have some more concrete advice on exit pupils, etc.

[The60mmKid]

49 minutes ago, The60mmKid said:

Greetings,

I'm moving to London in a few weeks. I'm an adept starhopper, but I'm accustomed to observing under Bortle 3-7 skies. So, I'd be grateful for suggestions on equipment and skills for urban starhopping (e.g., size/FOV/exit pupil of finderscope?). I am not interested in converting to go-to! I am considering setting up my 60mm refractor to use as a superfinder for my 5" refractor... 5.13° FOV, 4.53mm exit pupil. Good enough, or greater FOV needed due to a lack of naked-eye reference stars?

Thank you!

The Kid

I think I might have solved my own problem... 6x30 (7.5° FOV) finderscope = finder for 60mm refractor (5.13° FOV) = finder for 5" refractor. I think that might cover it. I think sometimes just writing out the question helps uncover the answer.

[The60mmKid]

11 minutes ago, Zermelo said:

Hello

I expect you will be navigating using a combination of optical finder and a widefield eyepiece in the main scope.
If you don't already have it, I'd suggest decent planetarium software (I use Skysafari):

(1) you can easily vary the magnitude depth of the view, and "tune" it to match what you're seeing in whichever instrument you're using

(2) it can show TFOV circles for the finder and any eyepiece/scope combination you care to set up. These can be used during sessions, or ahead of time to plan hops.

(3) you can easily flip up/down and left/right as you switch between finder and main scope (if that's necessary, depending on the optical properties of each)

I'm not sure about the value of unit finders in those conditions. I'm lucky enough to have Bortle 4, so there's normally plenty to go at, but when the moon is full my Telrad isn't too great.

There is this book, which is mostly about the objects you can find, even in polluted skies, but does also include some general discussion about techniques and equipment for urban settings. If you are experienced already, though, it probably won't have much to surprise you on that score.

City-based members may have some more concrete advice on exit pupils, etc.

Thanks for this wonderful response. I'm averse to using software/screens while observing, relying on my good old red headlamp and printed atlases. The book that you linked looks great, though, so I will get my hands on a copy.

[Oldfort]

I have tried star hopping from London skies, and gave it a really good go a few years back.  I couldn't do it and bought a goto scope, which has been great.  I did however learn that not all finders are created equal, and some of the cheaper ones performed better than the more expensive ones (the Skywatcher evo 50mm being an exception).

I didn't have the benefit of having learnt the craft under dark skies, and I hope your experience is better than mine.  But having said that an alt/az goto or push to doesn't take much time to set up.

[Mr Spock]

Skies are often bad here - mag 3.2 the other night and 4.5 on the best nights. Some thought it was amusing I use a 30mm 70° or 42mm 72° in the main scope as a finder. Well, a traditional 9x50 finder is useless - I can barely see any stars in it.

What I do is find the nearest bright star with a RDF, then hop from there. Charts oriented for the scope with diagonal help and I can usually find what I want easily enough.

I also don't like goto - takes out half the fun and doesn't necessarily find what I want.

[Ratlet]

53 minutes ago, Mr Spock said:

Skies are often bad here - mag 3.2 the other night and 4.5 on the best nights. Some thought it was amusing I use a 30mm 70° or 42mm 72° in the main scope as a finder. Well, a traditional 9x50 finder is useless - I can barely see any stars in it.

What I do is find the nearest bright star with a RDF, then hop from there. Charts oriented for the scope with diagonal help and I can usually find what I want easily enough.

I also don't like goto - takes out half the fun and doesn't necessarily find what I want.

I've got good skies but terrible eyesight even with glasses and seldom see below mag 4 without an an optical aide.

I've only ever done the same as Mr Spock.  I guess it will depend on the FOV you get but I found it easy enough with a 32mm plossl in my 130pds with a 2.8° FOV.  

I do use skysafari though with it setup to display the scopes FOV with my eyepieces so I can easily find my way around.

I think I've used my finders about once, telrad and a wide FOV eyepiece the rest of the time.

[bosun21]

3 hours ago, Ratlet said:

32mm plossl in my 130pds with a 2.8° FOV.  

2.5 degrees FOV assuming you took the 32mm plossl to be 52 degrees.

[Guest]

Get an adjustable setting circle and angle gauge.  A quick check of the app for the coordinates and boom you will be close.  

[PeterW]

As noted you can we many stars in a finder scope. If you’ve got a friend, then I’d use binoculars and a laser. A decent pair of binoculars will let you find your object location quite well, unless you’re moving to the most directly light polluted part of London. Then you point the green laser at the object location (being careful as always), your friend then sweeps the scope to align to the beam. Another option would be to find the location with binoculars and then punting the laser down the eyepiece of the normal Finder and put the beam on the memorised object location.  Of course I’ve also use Mr Spocks jumping, but sometimes there aren’t enough stars or it’s a long hopping exercise. Which bit of London are you joining?

Peter

[Ags]

I have Bortle 8 skies and use a 50 mm finder to star hop. Like Mr Spock, I point myself at something bright and work my way from there. Mag 7 or even Mag 8 stars are visible in the finder and that's enough to get me where I'm going. It may be a personal thing, we don't all see the same thing in a finder scope.

I'm not used to star hopping in dark skies and when I do, I struggle. Too many stars! 

[Ratlet]

1 hour ago, bosun21 said:

2.5 degrees FOV assuming you took the 32mm plossl to be 52 degrees.

I'm not sure what the FOV on the eyepiece is.  It's an svbony sv131 and I've seen as low as 42° and as a high as 55°.  I gave it the benefit of the doubt 😁.  Manufacturer claims 46° on their website and 48° on their website.

Works well as a finder eyepiece though.  Must admit I'm glad you pointed this out as I've been vastly underestimating how much of a step up the 2" superview is for a finder eyepiece.

[bosun21]

It’s actually 46 degrees for the SV131 giving a FOV of 2.25 degrees in your 130PDS.

 

Edited April 24, 2023 by bosun21
photo

[Mircea]

The Kid

I'm living in a 160.000 people city. It is easy to guess, you will have higher light pollution in London. But not by much, our local City Council is planting lights everywhere. I expect them one night ...  to sneak in and put a couple of light bulbs in the throne of my toilet.

According to old data of 2015  on ''Light Pollution Maps'', I had Bortle 6 sky at that time. Now is probably Bortle 7 or ''better''.

However, due to the method I acquired about six years ago, I continue to be successful in some Deep Sky observations.

I have three Dobsonian telescopes, of 125mm, 200mm and 250mm apertures.

The best for Deep Sky is of course the 250mm (let say ten inch). Last Thursday, on April 20, I managed to see with it 33 galaxies. 

16 galaxies were in Leo and 17 in Virgo and Coma Berenices.

The method, learned from the book of Rod Mollise, recommended to you by Zermelo, consist of using a joint finder : RDF and optical finder. I prefer now a RACI 8x or 9x50mm finder.

The 1x finder will drop you ''in the area'' and the optical finder to the ''exact address'' of the objects.

The method is brillliant, is working well. I am at peace with my self : if I cannot see the object, it is not because I don't find the location but because of the greedy local council who keep increasing the light pollution.

On ''Grond'', the 250mm Dobsonian, I received a Radiant finder which I think is similar to Telrad. This is doing the same work like RDF.

 

Even the 125mm f/ 6.9 Dobsonian aka ''Ugly Duckling'' is good for some basic Deep Sky observations with this method. In the picture you see only the bracket for the RDF.

My last observation with it  was Thursday , February 23. I was able to see Eskimo Nebula, M35, M37, M36, M44, M67 and M1.  And resolved 14 double/ multiple stars including 52 Ori, Eta Ori, 32 Ori.

 

I think you should consider the observation of double stars. It is very interesting, challenging and I see them as a kind of Deep Sky observation.

 

Don't give up observing. If someone really love Astronomy, that could be done anywhere. If the sky will be very bright, I will do the Astronomy of bright stars, learning more about the history and astrophysical properties of those extremely bright plasma monsters like Vega, Sirius, Deneb, Altair and so on, visible from anywhere.

 

Good luck, regards, Mircea

 

 

[Stu]

I agree about using and RDF/TelRad in conjunction with an optical finder. The biggest problem can be getting reliably onto a starting star, and that’s where the RDF really helps put you in the right spot. Once the known star is in your optical finder then it’s just the same star hopping game as a usual, but with a few less to choose from.

I know you are perhaps not keen on electronic help at the eyepiece, but I must say SkySafari on a phone is amazing for starhopping in light polluted skies. You can tune the field of view and limiting magnitude visible to exactly match the conditions, then hop away. It doesn’t affect your dark adaptation because that is pretty shot already by the LP! 🤪

[Ags]

4 hours ago, Mircea said:

Grond

Hammer of the Underworld 🙂

[Ratlet]

1 minute ago, Stu said:

I agree about using and RDF/TelRad in conjunction with an optical finder. The biggest problem can be getting reliably onto a starting star, and that’s where the RDF really helps put you in the right spot. Once the known star is in your optical finder then it’s just the same star hopping game as a usual, but with a few less to choose from.

I know you are perhaps not keen on electronic help at the eyepiece, but I must say SkySafari on a phone is amazing for starhopping in light polluted skies. You can tune the field of view and limiting magnitude visible to exactly match the conditions, then hop away. It doesn’t affect your dark adaptation because that is pretty shot already by the LP! 🤪

If you do want to preserve your dark adaptation you can get some red acetate sheet from ebay and stick it over the screen on your phone and turn the brightness down. I use an old phone so I don't have to take it off.  Skysafari can display the skychart in mono and it's pretty dim once setup.

The paid version lets you set an FOV for your equipment/eyepieces and you can tune the minimum magnitude for the stars so you can dial in the display perfectly.

[bosun21]

15 minutes ago, Ratlet said:

If you do want to preserve your dark adaptation you can get some red acetate sheet from ebay and stick it over the screen on your phone and turn the brightness down. I use an old phone so I don't have to take it off.  Skysafari can display the skychart in mono and it's pretty dim once setup.

The paid version lets you set an FOV for your equipment/eyepieces and you can tune the minimum magnitude for the stars so you can dial in the display perfectly.

Sky Safari can be used in night mode with a red screen.

[PeterW]

The ability to flip/rotate the field of view can really help you hop to the right location. It’s surprising what you can see from less than ideal skies.

 

peter

[Ratlet]

1 hour ago, bosun21 said:

Sky Safari can be used in night mode with a red screen.

Aye, the only problem I've encountered is if I lock or unlock the screen I get it back on at full brightness.  The acetate also helps dim it down slightly more than just dropping the brightness

[The60mmKid]

No phone! I'm going to fight to the last on this one! Taking a phone observing is like taking a pistol to church 😤 And now that I'm moving out of the US, that's even more frowned upon... 😉 Seriously, though, I understand the appeal. But observing is a sacred ritual for me, and I'm far too fond of my paper atlases.

Thanks for the suggestions, everyone. I appreciate the tips, especially the suggestion to incorporate binoculars. Rather than the RDF, though, I prefer a straight-through optical finder since I'm accustomed to star aligning/hopping with those. So, my current plan of action is to:

1. Start with my eyes...
2. Then step up to my 2x Galilean binoculars if needed...
3. Then step up to my 8x30 binoculars if needed...
4. Then step up to my 6x30 straight-through finder...
5. Then step up to my 60mm refractor, which offers a 5.13° FOV and 4.53mm exit pupil with my 40mm eyepiece...
6. And use that on its own and as a finder for my 5" refractor.

I'm probably just grossly overthinking this. I'm pretty adept at star hopping. I might be fine just plopping down and finding things 😁 But it's nice to have a 6-step plan in case!

Edited April 25, 2023 by The60mmKid

[The60mmKid]

(I also forgot to mention that double stars, and not faint fuzzies, are my passion, so I hope to keep enjoying observing even under the city skies.)

[Mr Spock]

Each to their own - some people do like their technology. I'm like you, just me, the scope and the stars. I can't comprehend taking a phone out with me.

I am thinking of going back a 9x50 finder to add to my 100mm - just so I can find 5th - 6th magnitude stars. I have a couple sitting around.  Naked eye I'm not getting much below 4 most nights and some parts of the sky are now almost bare. Recently I've not been able to see Cancer at all  If I can find a 5th magnitude star in the finder I can star hop from there with the main scope.

[Stu]

As you say, each to their own, and it is nice to respect every way of observing. It’s not technology for technology’s sake, it is genuinely useful and many on here, myself included find SkySafari an invaluable tool for finding targets, particularly unusual ones or dare I say it, lists of interesting doubles.

@The60mmKid, I still think you may find a step including an RDF useful as it gets your finder more easily into that first star, but see how you go.

[Ratlet]

Sound like you've got a plan.  And given me some dangerous thoughts about the FOV with a 60mm refractor...