Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
|
|
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate. For jupiter, the scope slews almost to it, but it does not appear in the eyepiece. In the viewfinder scope, jupiter is just a little to the right and down from the cross-hair. So, the calculation is almost accurate but requires some adjustment.
With jupiter, this isnt a problem since it is easily seen in the viewfinder. But what about uranus neptune and pluto? I have tried to look for them manually but I cannot tell them apart from the stars even if I did find them.
I have asked about the accuracy of planetary goto slewing in different threads before. It seems that if your scope can perfect slew to all objects except planetaries, then it is working fine, which is my scope's case.
So with that being the case, how do you find these planets?
--------------------
Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
|
veebs2
sage
Reged: 03/13/07
Posts: 206
Loc: DeKalb, IL
|
|
To find Uranus and Neptune, I use Pocket Stars on my phone to give me up-to-date Alt/Az coordinates. I then use my manual Push-to degree circle and digital angle finder to the get me to the spot. I found Neptune in under 30 seconds  on Saturday night. It had a definate blue disc.
--------------------
Paul
Zhumell 10" (My Mistress - name given by my wife)
Hyperions - 5mm, 13mm and 24mm
Stratus - 8mm and 17mm
Howie Glatter 2"-1 1/4" Holograpic w/ Barlow
Lumicon OIII Filter
Telrad
DeKalb, IL
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 6785
Loc: Beatrice, Nebraska
|
|
Quote:
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate. For jupiter, the scope slews almost to it, but it does not appear in the eyepiece. In the viewfinder scope, jupiter is just a little to the right and down from the cross-hair. So, the calculation is almost accurate but requires some adjustment.
With jupiter, this isnt a problem since it is easily seen in the viewfinder. But what about uranus neptune and pluto? I have tried to look for them manually but I cannot tell them apart from the stars even if I did find them.
I have asked about the accuracy of planetary goto slewing in different threads before. It seems that if your scope can perfect slew to all objects except planetaries, then it is working fine, which is my scope's case.
So with that being the case, how do you find these planets?
Well, Uranus and Neptune will usually appear somewhere in a low-power field of view of my go-to scope (a NexStar 9.25). Usually, the "miss" on solar-system objects is less than about 20 arc minutes. Uranus and Neptune are somewhat bluish in color and have disk sizes that are large enough to stand out as tiny disks at from 98x to 168x, so I find them quite easily (I looked at both last week from my driveway with a fat gibbous moon in the sky). Pluto is somewhat more difficult, as the scope will get it in the field of view, but it just looks like a very faint star. I usually have to use one of my star charting software packages like MEGASTAR to show me the field and help identify which faint star is Pluto. Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
|
Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
|
|
Quote:
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate.
Well, actually all objects are calculated, and if the planets are not accurate, then they are calculated poorly or incorrectly.  It's a nit-pick, I know. Still, I've seen this complaint floating around before. I wonder whether the hardware that's usually used to handle these is not up to the task of performing the correct calculation to the required precision...
Chris
--------------------
"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
|
Joe Lalumia
Carpal Tunnel
Reged: 01/24/07
Posts: 2573
Loc: Rockwall, Texas, USA
|
|
If you press GOTO again after the scope has slewed to the "apparent" location (with a Meade hand controller), the scope will do a spiral search to sweep up objects just outside the field of view.
--------------------
LX90 8" LNT, SV Nighthawk & TelePOD, SV 80/9D & M4 mount, ETX 90, Orion XT10i, 20x80 binoculars, SV-BV3s.
"The hardest thing in the world to understand is the income tax." - Albert Einstein
|
fastrudy
super member
Reged: 04/09/06
Posts: 164
|
|
all planetary objects are calculated which means they are not 100% accurate.
You need to refine your alignment. When you center the alignment stars in your eyepiece, change to a higher power and carefully center it. Uranus is a blue disc, Neptune a green-blue and Pluto is star-like, and must be identified by consulting a good star map. You may have better luck. My Meade comes with a 'spiral search' feature which slowly spirals out of the initial position and you can search for the intended object. A nice feature.
--------------------
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 6785
Loc: Beatrice, Nebraska
|
|
Quote:
Quote:
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate.
Well, actually all objects are calculated, and if the planets are not accurate, then they are calculated poorly or incorrectly. It's a nit-pick, I know. Still, I've seen this complaint floating around before. I wonder whether the hardware that's usually used to handle these is not up to the task of performing the correct calculation to the required precision...
Chris
In the case of my old NexStar 9.25, the calculated planetary positions are reasonably accurate, but the instrument's ability to reach those locations and get the scope pointed precisely to the desired spot is less than dead-on. Generally, with some care, the scope will be able to point within 5 to 13 arc minutes of where I wanted it to go, so I generally don't use a "finding" field of view smaller than 26 arc minutes in diameter if I hope to find something. Luckally, even my 14mm Ultrawide (168x) gives me a true field of 29.7 arc minutes, so most of my quarries are still within that field even at that power. Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
|
Kolenka
professor emeritus
Reged: 06/01/08
Posts: 600
Loc: Seattle Area, WA, USA
|
|
Quote:
Quote:
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate.
Well, actually all objects are calculated, and if the planets are not accurate, then they are calculated poorly or incorrectly. It's a nit-pick, I know. Still, I've seen this complaint floating around before. I wonder whether the hardware that's usually used to handle these is not up to the task of performing the correct calculation to the required precision...
Chris
Actually, there is a fairly technical difference between 'calculating' the position of a star, and calculating the position of a planet. RA/Dec coordinates to Alt/Az are fairly well known calculations, as is figuring out the current orientation of 0h to account for the date/time. And this is really all that is done for stellar/DSO objects. This is simple, straight-forward, and well known.
The calculations for a planet are much more complex because they aren't fixed in the sky, they orbit the sun like we do, and getting precise coordinates isn't so simple. Even using an internal Newtonian model of the solar system, the coordinates will drift a bit after awhile (how long I don't remember). And such a complete model probably wouldn't fit the RAM/ROM limitations of these scope computers. So they use an estimation formula with a 'seed' value (coordinate at a certain point in time) to calculate the estimate.
One way to get better planetary pointing is to use a more accurate planetarium application and have it feed the RA/Dec coordinates to the scope via an RS-232 cable.
--------------------
Meade 10" LX200R
Orion 80ED
Nagler 7T6, 9T6, 13T6, 17T4, 26T5
Canon XSi (Modded), TIS DMK 31AF03
Northwest Astro Photoblog
|
Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
|
|
Quote:
Quote:
I have a fully goto scope, but the problem is that all planetary objects are calculated which means they are not 100% accurate.
Well, actually all objects are calculated, and if the planets are not accurate, then they are calculated poorly or incorrectly. It's a nit-pick, I know. Still, I've seen this complaint floating around before. I wonder whether the hardware that's usually used to handle these is not up to the task of performing the correct calculation to the required precision...
Chris
No, planets are calculated differently than everything else.
That is why on my scope, all dsos, all stars, all galaxies....basically every single object slews to the center of the eyepiece. It is only the planets on my scope that are off a bit.
It doesn't have much to do with my accuracy of alignment. I use a very accurate compass to achieve true north, and i bring the dec to 0. When i center the 2 alignment stars in the eyepiece, I use 250x at least magnification.
I then test the accuracy of the alignment by randomly selecting objects that require a vast change in slewing. Like I would go from lagoon nebula, to ring nebula, to dumbell nebula, to andromeda galaxy, to M2, to M13...and so on. Basically I throw the scope around all night slewing wise, and I have done this for almost 8-9 hours strait on some nights when i was testing my electronics. The scope maintains accurate alignment from the very first time you do it...and keeps it for 9+ hours.
When it slews to planets, the crosshair of the view finder appears a little bit north west of the planet. So, of course the planet will not be inside the eyepiece. Since it appears to be the same amount of error every time, night after night, I am positive that it is the telescope calculations that are going wrong...nothing that I can change by improving my alignment.
This problem has been confirmed by countless fully goto SCT users. Most SCTs will have the problem of not having fully accuracte planetary slewing. However, once the scope slews right near the planet...you can center it in the view finder...and boom it will be in your eyepiece for the entire night. The tracking of the targets is flawless no matter what target it is....but it is only the slewing goto that is a bit off.
Thank you guys for giving me some tips on how to find the planet.
"If you press GOTO again after the scope has slewed to the "apparent" location (with a Meade hand controller), the scope will do a spiral search to sweep up objects just outside the field of view."
Will this feature work on the EMC coated lx-90s that were made in 2000-2004? I have heard of this feature but never tried it. My autostar has he high precision feature, and also has the feature to change the alt and az ratios...which is a fairly newer feature of the autostar gotos.
--------------------
Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
|
molniyabeer
Carpal Tunnel
Reged: 01/08/05
Posts: 2062
Loc: Central Coast, California
|
|
FWIW, my dad has reported Jupiter being consistently off in his Mead LX-90 (8"). Everything else will come in dead on. Maybe a glitch in their database?
Uranus and Neptune are well within your scope's limit. I have tried on three nights from a moderately dark site with my 10" dob and am only moderately confident that I found it. I had good charts, know the star hop was dead on, and just couldn't see the blasted thing! At mag 14 it's *really* faint. Averted vision just got fleeting glimpses of it. So I think an 8" would require a really dark sky to pick up Pluto.
Clear, dark skies.
--------------------
Steve
16" Meade LightBridge (Beowulf)
10" Hardin DSH, StarMax 127mm Mak, PST H-a
Oberwerk 11 x 70 binocs, Tasco 10 x 50 binocs
Santa Maria Clear Sky Clock
Figueroa Mt Clear Sky Clock
|
Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
|
|
Quote:
No, planets are calculated differently than everything else.
They'd have to be. Remember, planets are really the only things in the database (maybe some other exceptions too, depending on your scope) that have an orbital period smaller than the expected lifetime of the instrument. For most of the other stuff you really don't have to do that kind of calculation, but calculations are required, nonetheless.
Chris
--------------------
"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
|
JAT Observatory
Space Freak
Reged: 02/20/05
Posts: 5656
Loc: Eastern PA
|
|
Brooklyn,
Kolenka gave to the best option in my opinion:
"One way to get better planetary pointing is to use a more accurate planetarium application and have it feed the RA/Dec coordinates to the scope via an RS-232 cable"
Or if you didn't want to hook a PC to the scope you could just enter the co-ordinates into the handbox and then have the scope slew to the planet.
--------------------
-Marcus
The problem with free speech is even the stupid have a voice.
http://jatobservatory.org
12" LX200R on a Paramount ME
|
Tony Flanders
Carpal Tunnel
Reged: 05/18/06
Posts: 2103
Loc: Cambridge, MA, USA
|
|
Quote:
No, planets are calculated differently than everything else.
That is why on my scope, all dsos, all stars, all galaxies....basically every single object slews to the center of the eyepiece. It is only the planets on my scope that are off a bit ...
When it slews to planets, the crosshair of the view finder appears a little bit north west of the planet. So, of course the planet will not be inside the eyepiece. Since it appears to be the same amount of error every time, night after night, I am positive that it is the telescope calculations that are going wrong...nothing that I can change by improving my alignment.
You're right; calculating the positions of the planets is quite different from calculating the positions of the stars. However, there's frankly no excuse for a Go To telescope to do it wrong -- though some apparently do. It's quite easy to calculate the position of a planet accurately enough to center it in a low-power telescopic field of view. A power series with 30 or 40 terms does the job nicely.
I will, however, point out that your problem could be due to an incorrect date/time -- for instance, to not correcting for daylight-saving time. Once the scope is aligned, errors in time and/or location will have no effect on locating stars, but they will affect the positions of the planets. And they'll cause huge errors in the position of the Moon.
In answer to your question: It sounds as though you're going to learn how to star-hop. Go To drives can put off that need, but sooner or later you're bound to need it -- for instance, to find your way around fields of faint galaxies. In this case, a specific inadequacy of your Go To drive is going to force you to learn how to use star charts sooner than you might otherwise.
--------------------
Tony Flanders
eyeglasses
6x15 and 8x32 monoculars
8x25, 7x35, 10x30 IS, 10x50, and 15x70 binoculars
70mm and 100mm achromatic refractors
4.5", 7", and 12.5" Dobs
|
Cames
member
Reged: 08/04/08
Posts: 14
|
|
Like you, I have found Pluto a challenge using similar equipment, detailed charts and dark skies. Fleeting glimpses only occasionally a little more. The frustrating thing is that 14 to 14.4 mag stars in the vicinity are often visible with direct vision.
I have always noted a 'visibility' discrepancy with the magnitude values assigned to extended objects like planets, etc. To me, a 14 mag Pluto is not as easily observed as a 14 mag star.
C
|
Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
|
|
Quote:
Like you, I have found Pluto a challenge using similar equipment, detailed charts and dark skies. Fleeting glimpses only occasionally a little more. The frustrating thing is that 14 to 14.4 mag stars in the vicinity are often visible with direct vision.
That's the frustrating thing? I'll trade you for my night sky...
Chris
--------------------
"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
|
FoxK
Carpal Tunnel
Reged: 11/07/07
Posts: 1804
Loc: Cape Cod, MA
|
|
Like most posters, even when fine tuned at polar alignment and I see slewing to DSO's dead on, when I go to planets...its far from accurate
--------------------
Orion 80mm ED Apo Refractor
8" Classic Dob (used as Newtonian on CG5 mount)
Meade 70-AZ-A 70mm Guider using PHD
LS60TCaK/B600/C
CG-5 Advanced GT Mount
Nikon D40x with T-Adaptors
Philips SPC900NC
Imaging Source DMK 21AU04.AS
Dome=the box my mount came in so I can see my solar images in bright sun lol
- click for cloud prediction for Plymouth, MA. area
|
Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
|
|
I think maybe the planetary positions could be a factor of another thing.
First off...when you enter your latitude and longitude into the meade autostar handbox, you can only enter things to the minute. The second space is not there.
So, my lat long is as follows:
40N 20' 22.6"
74W 15' 37.1"
Here is the only way autostar accepts these coordinates, and to the most accurate value:
N40 20'
W74 15'
I believe that the small constant error in accuracy could be due to this inaccuracy with finding a distinct observing site.
I thought about your suggestion tony, with the time or daylight savings being off. It could be possible, but it seems highly unlikely. I live in new jersey, so i choose YES for daylight savings. For entering the exact time...I enter the minute ahead of what my clock says. When my clock hits the next minute, i press enter...and thus it is almost on-point to the second accuracy. I think with this much accuracy, it really should not be making errors with planets.
Oh someone mentioned that the Moon will be the most error prone, followed by planets after it. This is 100% correct and my case confirms it. I do not think I have ever seen my scope slew to the moon accurately when I ask it to GoTo. It is usually off by a huge margin. Jupiter however, is only on error by a very small margin. When slewing to jupiter, the viewfinder always has the cross-hair to the northwest location of jupiter.
So, I have reason to believe that this error in planetary slewing is constant no matter what night or time I am observing. In beginning of july, it had the same amount of error on jupiter as it just had this week.
Are there any people here who have the LATEST version of autostar updated to their handbox? If you do did it help with planetary accuracy at all?
By the way for those using meade handboxes, if you HOLD the MODE button for 3+ seconds then release, you will get to a side menu. It allows you to enter your RA/Dec manually, and also to see all the info that the telescope is currently chomping on. You can observe things like battery level, date, location (lat/long), etc.
Considering all of this, do you guys have any more comments to add?
--------------------
Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
|
Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
|
|
Quote:
Brooklyn,
Kolenka gave to the best option in my opinion:
"One way to get better planetary pointing is to use a more accurate planetarium application and have it feed the RA/Dec coordinates to the scope via an RS-232 cable"
Or if you didn't want to hook a PC to the scope you could just enter the co-ordinates into the handbox and then have the scope slew to the planet.
Would Stellarium be the most accurate RA/dec spitter outer? I love that program and its purtey graphics.
Any other suggestions where to find RA/dec for any given time aside from the free star chart programs?
--------------------
Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
|
Tony Flanders
Carpal Tunnel
Reged: 05/18/06
Posts: 2103
Loc: Cambridge, MA, USA
|
|
Quote:
I believe that the small constant error in accuracy could be due to this inaccuracy with finding a distinct observing site.
One arcminute of latitude or longitude is a trivial error; that can't be the problem.
Quote:
I thought about your suggestion tony, with the time or daylight savings being off. It could be possible, but it seems highly unlikely. I live in new jersey, so i choose YES for daylight savings.
How about time zone? If the computer thinks you're using GMT instead of EDT, that will introduce a 4-hour error, which is really quite a lot.
Quote:
Oh someone mentioned that the Moon will be the most error prone, followed by planets after it. This is 100% correct and my case confirms it.
There are two explanations that would cover that fact. First, if it is really a problem with time, then the closer the object, the bigger the error will be. The Moon traverses the ecliptic once a month, as opposed to once every 12 years for Jupiter.
But if it's a computational problem, the Moon would also be most likely to be wrong. Because it's powerfully affected both by the Sun and Earth, the Moon's orbit is notoriously difficult to calculate. Vastly harder than the planets.
Quote:
In beginning of july, it had the same amount of error on jupiter as it just had this week.
Mmm, that appears to rule out an error w.r.t. time. Jupiter was moving through the stars much faster in July than it is now. In fact, it will be stationary on Sep. 9.
--------------------
Tony Flanders
eyeglasses
6x15 and 8x32 monoculars
8x25, 7x35, 10x30 IS, 10x50, and 15x70 binoculars
70mm and 100mm achromatic refractors
4.5", 7", and 12.5" Dobs
|
Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
|
|
tony for my time zone, I live on the east coast.
In my meade autobox i enter -5 for my time zone.
This is confirmed by the instructions in the meade instruction guide and by weazners etx site...
"There is a serial command for changing Time zones. It's :SGhh.h#
where "hh.h" are the numbers to -add- to UTC to get local time.
So the sign is inverted from Time Zone practice. If you're in
the Eastern US, you'd set a "-5" as your Time Zone, but you'd
send :SG5# (positive five) serially."
http://www.weasner.com/etx/archive/feedbackOct06/autostar.html
So yep, I put in -5 for eastern time zone, with accurate time to the nearest 2-3 seconds, and I select YES for daylight savings time.
I don't know tony, I have a feeling that there is not much I can do in terms of my accuracy to fix the problem. If all people using a SCT goto are having the same problems, even with newer versions of autostar, then all I can do is wait for meade to release a newer autostar version.
This is a good thread for new SCT users...they might have everything accurately entered, and then they would be wondering why their planets are not centered in the eyepiece.
--------------------
Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 