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Determining whether skies are dark enough for star hopping?

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#26 aeajr



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Posted 15 April 2018 - 09:16 AM

I'm new to the hobby and forum, and curious if any of you have found ways to assess whether skies are dark enough to star hop satisfactorily.


A bit of background, I'm brand new to the hobby, for the past few months I've been having a great time getting to know the sky from my backyard with the S&T Pocket Sky Atlas and some cheap 10x50 binoculars. Although I'm not in a rush to get a scope, I can of course come up with plenty of rationalizations for doing so sooner rather than later. Based on this site and the handful of books I've read, I'm more or less convinced to get a dob (maybe this 8" from Skywatcher?), which would see most of its use in my urban backyard (naked-eye limiting magnitude 4.5-5.0). But I've also read a number of well-informed opinions suggesting that goto or push-to is very useful, bordering on necessary, in bright skies.


So, I'm wondering if there's a test like 'if you can find your way to [a somewhat out-of-the way, but still detectable in bright skies binocular object] with binoculars, then you probably have a sufficient combination of darkness/patience to manually find objects in a telescope to your satisfaction.' I'm expecting a learning curve with whatever scope I get, but want to make sure I have realistic expectations for my ability to find things with a manual scope. I imagine I'll spend most of my time at least initially on clusters, planets, and interesting stars (basically, whatever can be seen from my backyard).


My thanks in advance for any insights you all may have - I've loved reading these forums, and have found no other corner of the internet that is so insightful while also being so pleasant and welcoming!


Cheap 10X50s is how I got started.    Got mine at Harbor Freight for $20.  Worked with a Planisphere.


Your sky is darker than mine.   In the darkest part of my sky I can barely make out mag 4 with averted vision.  In most of my sky there are very few stars visible to the naked eye.  


GoTo and PushTo are very helpful.  My first scope was GoTo and it was great.  I have 3 scopes now, 2 GoTo and 1 PushTo.  But I do star hop and I do use other techniquest to find targets.  So having a computerized mount does not prevent you from manually hunting IF you can release clutches to move the scope manually.  Also, virtually any GoTo mount can be used with the arrow keys to star hop although I think I would find it tedious. 


Thanks to all with the helpful suggestions. NEOhio & ff., I appreciate the guidance on finders. I was wondering if there was some way in which sighting targets through a straight-through finder mounted to a telescope was easier than it looks, and it seems the answer is 'no'. Mariner 2 and Gemini, thanks for your encouragement along the star-hopping path, and I'll definitely take to heart the suggestion to explore binocular objects to gain more familiarity with finding my way around the sky. I had a great time last night finding M3, which granted is close to a bunch of bright stars and even in my skies is hard to miss if you pan over it, but still, the search was a good part of the fun. Thanks again!

When star hopping I often do the hop with my 10X50s first.  On the scope, an 8" Dob, I have a 9X50 RACI ( right angle correct image) finder and a red dot finder, RDF.  I find the RACI and the RDF a great combination.  Some people team a RACI with a Telrad, also a great combo.


But to my West and much of the South there are very few stars in the sky.  Even with the RACI and the 10X50s I can't see much in starts.  So star hopping in those areas can be more of a challenge than I care to take.


Do your star hops with your 10X50s.  If you can't see them in the binos you are not going to see them in the finder scope.  And note that you can see more in binoculars than you can see in a comparable aperture and magnification finder.   8X50 binos will show you more than an 8X50 finder.


Thanks to all with the helpful background on different aids for finding your way around. It sounds like between a finder scope, telrad/red dot, and setting circles, there are lots of strategies for finding your way around the sky even in bad conditions, it's a question of figuring out what suits you best. Jon, thanks for the rundown on your process, seems to have served you well. I love SkySafari by the way, I can think of few 99c that I've spent better. Analogkid, I'll certainly follow your advice to check out a club near me (Richmond, VA) so I have a sense of what I'm getting into. I'll report back on what ends up working for me, although it may be a few months - my wife and I are expecting our second child any day now and I certainly don't need an additional thing that keeps me up all night at this point smile.gif.


These are discussions you might find interesting in the context of your question.



Using an angle gauge to help find targets



Favorite methods for finding targets


EZ Push To from Romer-Optics
A retro fit PushTo package is available from Romer-Optics called the EZ Push

This fits on select Dobsonian telescopes.
This is based on using your phone as the computer/controller – About $100
https://www.cloudyni...l=+ez +push +to
Installation Video
Quick Start Guide
Romer-Optics EZ Push To Page
Stellarium Plug-in

Edited by aeajr, 15 April 2018 - 09:48 AM.

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#27 aeajr



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Posted 15 April 2018 - 09:20 AM

Here is a way to put your star hopping ability to the test. 


Create a list of targets sorted by constellation using Tonight's Sky -


  • Run a list of targets
  • Using your chart, figure out the star hops
  • Now, go do those star hops with your binoculars

If you can't see the stars to do the hops with your binos you won't be able to see them in an 8X50 or 9X50 finder and you certainly won't be able to see them with a RDF or a Telrad.


Note that with a telescope you can use a low power wide view eyepiece as a next step finder.   On my Orion XT8 Intelliscope, when I choose to star hop, my sequence is:

  • 10X50 binoculars (6 degree FOV)
  • RDF to get to the starting point, usually a bright star
  • RACI 9X50 to do the hop (5 degree FOV)
  • 2" 38mm 70 degree AFOV eyepiece (2.2 degree FOV 31.5X)

In the worst part of my sky, even with the 2" 38 mm I sometimes can't see the guide stars or the target.  I might be on it and still can't see it. 


A few nights ago I was going after M5, a globular cluster, in the SE part of my sky.  Not the worst part of the sky but there are very few visible stars in that area. Not great star hopping. 


I used Jupiter as my starting point.  Could not see the guide stars I was looking for in the 9X50 RACI.  So, I used degrees of FOV to get into the general area.  Similar to the technique described in the quick start guide at the link below.  This is also similar to how a Telrad is used.


I was in the area but I could not find it in the 9X50 RACI finder.  So I went to the 38 mm eyepiece in the Dob.  A little sweeping back and forth found it.  It was not visible in the finder but it was visible in the telescope eyepiece as a light gray fuzzy against a darker gray background sky.   Easy to miss, but I found it!



So, again, do the star hops with your binoculars.  They will be a good test of whether star hopping is going to work for you.  And, if star hopping doesn't work, you can use the angle gauge method described in my previous post.  I have had great success with that even in the worst part of my sky.  Or you can decide to go for a PushTo, like the Orion Intelliscope I have, or one of the GoTo systems. 



You might also find this article interesting - written for binocular users


Edited by aeajr, 15 April 2018 - 09:46 AM.

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#28 Asbytec


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Posted 15 April 2018 - 08:33 PM

There's a lot of good experienced advice here. Myself, I do have a hard time star hopping during a full moon, even with a finder. But, is there an easy answer to say the sky is dark enough? Or conversely, too bright? I think not, cuz like anything it depends on a number of things and there are ways around it. You just have to go do it and see. I could star hop with a full moon, it was just more difficult because some of the stars were harder to see. When that happens, star hop at low power through the scope itself. Sometimes we need to do that, anyway. So, it /may be/ the sky is never too bright (same as dark enough), save for daytime, to get to where you're going. 

Edited by Asbytec, 15 April 2018 - 08:35 PM.

#29 aeajr



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Posted 16 April 2018 - 10:04 AM

One additional thought on star hopping.


You may do the star hop correctly and still not see the target.   This has to do with how dim the target is, in the case of stars and planets.   You can get to the right spot but, depending on the aperture of your scopeyou may still not be able to see it.  In the case of galaxies and nebula the key thing to be aware of is not magnitude but surface brightness and the phase of the Moon.  


For example, let's use the North America Nebula.  This nebula is huge.   According to Stellarium it is a Mag 4 object.  Now, you look at that and say, wow, I should be able to see that naked eye.   But likely you can't.   


OK but with my binoculars I should be able to spot it easily.  And maybe you can, but I can't.  In fact I purchased a low power wide view eyepiece for my 8" Dob specifically for this Nebula, but can't see it.   I picked up Nebula and OIII filters.  No Joy!   And I have computer assist on my XT8 intelliscope so even if I didn't do the star hop correctly the Intelliscope should get me there.   NADA!


Until I came to understand the difference between magnitude and surface brightness, with the help of the fine people on Cloudy Nights, I was very frustrated.   I had an 80 mm Goto scope looking for a Mag 4 target and I could not find this Nebula.   I tried with my 8" PushTo XT8 Intelliscope and I could not see it.  


I am in a darkwhite area, the second worst. 




The key is surface brightness.   While the magnitude it 4, the surface brightness is 13.9 which is very dim.   No matter what I do from my home site, no matter the phase of the moon and no matter what filters I use, I can't see this huge nebula from my home location.  And I have the same issue with many galaxies.


The key is contrast between the surface brightness of the target and the brightness of the background sky.  I have so much light pollution in my sky that the background glow is close to or higher than the surface brightness of the nebula.  So I can't see it.    


The only reason we don't see stars during the day is because the sky is brighter than the stars.  So it is at night with light pollution.  If the background glow of the sky is brighter than the target, you won't see it regardless of whether you star hop or use Goto.


So I have learned to pick my targets based on my location.  At home I focus on stars, double stars, clusters, planets, the Moon and brighter nebula like the Orion Nebula.   I don't go after most other nebula or galaxies.  The brighter Messier globular clusters are just gray gray fuzzies from my home.   Even if I find them, as I did  M5 the other day, They are just faint gray fuzzy patches against a slightly darker gray sky.  


But if I go to a somewhat darker area, say a dark red or darker, all of a sudden things start to appear and some of those gray fuzzies start to show form and shape.  M31, the Andromeda galaxy, is a gray fuzzy blob from my home but at a dark red site it has shape and form.  Not a lot of detail but much better.    Under a darker sky it is a naked eye visible target.


You are in a darker area than I, but this can still be a factor, especially when the moon is bright.  So, keep this in mind when picking your targets or you will be frustrated in your star hopping.  Even if you can't see it, it doesn't mean you did the hop wrong.   When star hopping with your binoculars, start with brighter objects and then work your way down to see how dim you can go.

Edited by aeajr, 16 April 2018 - 10:53 AM.

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#30 zleonis


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Posted 16 April 2018 - 02:59 PM

Thanks again to everyone who's weighed in with their techniques and experiences. Aeajr, thanks for the terrific links, especially to the 'what can I see tonight?' and yours (and others') methods for finding things in less than optimal conditions. It sounds like planning and expectations are especially important, and that conditions are at least as likely to limit what you can actually see as your route to it. 


I had a chance to go to a local astronomical society event and they were all very helpful and let me check out the club's outreach scope, an Orion XT6. I was glad to have some of the background you all had shared. The stock red dot finder seemed fine for stuff nearby bright stars (got to find and see Orion Nebula and σ Orionis through a scope for the first time!), but some sort of magnification would definitely be necessary for targets more difficult than 'find Alnitak and then, like, nudge the scope down a little bit.' But it sounds like the sense of the community is that a scope with the right finders can get me to most of the targets that I'd be able to see, especially with more experience with the scope and familiarity with the sky. After talking with you all, if/when I do get a telescope, I'm leaning towards the Apertura AD8. It sounds like the optics are comparable to the Skywatcher/Orion models, and the included accessories like the 8x50 RACI and the wider field you can see through the included eyepieces are worth the additional cost. Really appreciate the community's thoughts!

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#31 aeajr



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Posted 16 April 2018 - 04:29 PM

Apertura 8 would be an excellent first scope and the package has great accessories.


Remember that for star hopping, multiple finders is not unusual

  • Red Dot, Telrad or similar non-magnified 
  • 6x30, 8X40, 9X50 or similar magnified finder
  • Low power wide view eyepiece. 

A progressive team


Use those binos and be sure to look over that quick start guide.  


New Astronomer Quick Start Guide - based on binoculars

Edited by aeajr, 16 April 2018 - 04:31 PM.

#32 Jon Isaacs

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Posted 17 April 2018 - 05:29 AM

Jon, I was thinking further about what you said. My cell phone screen dims, anyway. It has a slider that controls it. I may try to find the Dimmer app to help. Because, you're right. We do need to focus on the importance of dark adaption and taking steps to not lose it. I know I blow mine during star hopping, I just don't know by how much. The Sky Safari screen is not too bright, not compared to a web page or text message. The stars seem to be okay, and the text on the screen maybe, but the menu at the bottom all probably adds up to some amount of light pollution. Once someone texts me, if I read it...I'm done for a while. (LOL) 




The main issue with cell phones and tablets is the light leakage.  Unless your phone has an AMOLED/OLED screen, black is not really black so the entire screen is leaking white light.  If you ever see someone with a phone at a distance at night, you can see how their face is lit up.


So, in addition to dimming the screen and using a red theme, using a red filter of some sort over the screen is a necessity.  I use the Orion red goggles.  The effect is quite dramatic.  The goggles block the screen leakage of anything that is not red so the contrast is improved and the brightness lowered even more.  


I find under dark skies, I can use the tablet with the red googles, screen dim etc and it doesn't seem to affect my night vision.  I do keep the brightness to an absolute minimum, so the screen is somewhat difficult to read.  I also use extra strong reading glasses so I can be closer the the screen.


From my urban backyard, I am not so careful, I don't bother with the red goggles, there's enough light pollution that I am not so concerned about my dark adaptation.  



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#33 Jon Isaacs

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Posted 17 April 2018 - 05:48 AM

After talking with you all, if/when I do get a telescope, I'm leaning towards the Apertura AD8. It sounds like the optics are comparable to the Skywatcher/Orion models, and the included accessories like the 8x50 RACI and the wider field you can see through the included eyepieces are worth the additional cost. Really appreciate the community's thoughts!




I think the Apertura Dobs represent a better value than the Orion/Skywatchers.  Apertura Dobs are manufactured by Guan Sheng Optical (GSO) in Taiwan and there's something of a story behind all this.. 


It was back in 1999-2000 that Orion introduced the XT-6 and the XT-8, these were the first metal tubed Dobsonians and they were well received.  More finished than the previous generation of sonotube Dobs.  These were manufactured by GSO.. 


Soon enough, Orion switched suppliers from GSO to Synta Optical/Skywatcher which left GSO "holding the bag."  They needed to find someone new to market their scopes.  Over the years, there have been a number of end-sellers of the GSO Dobs. 


My 10 inch F/5 which is 2002 vintage was sold by Oceanside Photo and Telescope as the OPT Starhunter 10.  I bought it used in 2003, it has been a good scope.. I was never my biggest or "best" scope but it's a solid performer than holds it's own in a stable with some pretty fancy scopes.  


Without the massive advertising presence Orion has, GSO took the approach of providing a better product, a better value.  The early metal tubed Dobs all had rack and pinion focusers. serviceable but not optimal. Soon enough, GSO developed a simple but very nicely made Crayford.  Orion followed with a usable but somewhat lesser Crayford.  Soon enough, GSO upped the ante again with a 2 speed micro-focuser.  Today, that GSO 2 inch 2 speed focuser is a popular upgrade for not only Dobs but for refractors and other telescopes.  My 80mm F/6 apo refractor came stock with a GSO two speed. Besides being a good focuser, it's an attractive focuser, machined rather than casts.  


That philosophy can continued to this day, compete by providing a better value.  The standard 2 inch GSO wide field is a better eyepiece than the standard Orion/Skywatcher 2 inch.  The 50 mm RACI finder is a real plus.  This is not to say that the Orion 8 inch Dob is not a good scope, it is.  It's just that I think you get more for your money with an Apertura.



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