I am trying to help my grand daughters set up their Celestron SC telescope for use. We are having a couple of issues I hope someone can help me with
The first issue is star alignment. I do a manual polar alignment then go to the 2 star alignment process. The software slews to a star and asks me to centre it in the viewfinder and then in the telescope. The issue I am having is that the finder scope has too narrow a field of view for me to identify and centre the correct star. This happened with easily identifiable stars in the Southern Cross. I manually try to sight across the finder scope but still can’t identify the correct star through the finder scope
Should I look at getting a finder scope with a wider field of view or is there some other method?
The second issue is that the remote hand piece of the mount operates in azimuth using the up/down buttons and in elevation using the left and right buttons?
Hi Geoff, your finderscope problem is probably that the finder is not accurately
aligned with the scope; to do this, during daytime centre something such as
a street sign a couple of hundred metres away in the scope, and then adjust the finder until the sign is centred in the finder. Finders have a field of view of around 7 or 8 degs, which is about 15x the field of view of the scope at prime
focus; you certainly don't need a larger field of view than that.
There is no altitude and azimuth movement on an equatorial mount.
The axis that the counterweights rotate around is called right ascension,
and the axis that rotates the saddle that the scope sits on is called declination.
The left and right buttons operate the R.A. which moves the counterweights, and the top and bottom ones operate the Dec axis which rotates the scope left or right. If the polar alignment is accurate, the R.A. motor rotates the mount against the direction of the Earth's rotation, thus keeping the stars stationary.
raymo
Hi Geoff and welcome
The accuracy of the slew to the 1st alignment Star on any EQ mount is dependent upon how close your mount is set up in the start or Home position.There are 4 important procedures -
1/ Tripod facing True South
Your tripod should be placed down and aligned to True South , that is front leg together with the central axis of the other 2 tripod legs pointing to the South Celestial Pole or Meridian Line ( Not Magnetic South )
2/ Tripod Level
Make sure your tripod is level on all cardinal plains NSEW
3/ Mounts Altitude set to Local Latitude
Make sure your mounts altitude is set ( using the mounts altitude bolt) to the local latitude of your location ( I use a digital inclinometer with accuracy to 2 decimal places ) Leave the Azimuth Bolts centrally screwed in even ( not too tight ) on both sides of mount ready for your 1st star alignment adjustments)
4/ Set mount to Home Position
See my attached procedure
If the above procedures are done as accurate as possible, and your finder scope is aligned properly ( Raymo) and all your hand controller settings are correct time , date , location , hemisphere etc..... , then your first alignment Star should end up in the field of view of your finder scope and even your telescope
See attached ( Celestron mounts are similar to Skywatcher mounts for these procedures)
Thank you for the advice it is very much appreciated. I was definitely no paying enough attention to polar alignment - I had aligned the finder scope and the telescope
Had another try tonight with as precise polar alignment as I could achieve given the tools at hand. Used an iPhone app to align south - problematic in itself as each app showed south in slightly different directions. Used mount adjustments to dial in latitude as accurately as possible
This was close enough for me to do a 2 star alignment on Sirius and Canopus with some minor searching.
We then used the auto tracker to find a twin star - forgot the name close to the two alignment stars. The twin star appeared in the centre of the telescope
When I slewed to Mars however - not close to the alignment stars, it was visible at the edge of the finder scope view but not within the telescope view. I assume that this is to do with the accuracy of the polar alignment.
I am looking at purchasing a digital incline metre and considering purchasing a good compass
A compass will only give you magnetic bearings which you don’t want unless you apply the offset magnetic deviation to your location. If you still want a good compass try any orienteering compasses that are oil filled as these come to a bearing and sit there without oscillating rapidly. (Silva brand is good but there are others).
Best way to find true south is to find true north first using the Sun. You need a vertical stick and a horizontal surface. The true north-south line is the diretion of the shortest shadow. This is best done in winter as in the summer the shadow is short as the Sun is a lot higher.
I have used the Sun shadow method but I also use (and prefer for its speed) the the following method. Get any astronomy app whether on computer (PC) or mobile device. (You do not need the device outside). Stellarium is free so I’ll describe it.
Do this in the morning well before the Sun reaches its highest point in the sky so that you do not miss that point.
1. Make sure your location is in Stellarium.
2. Make sure Daylight saving is enabled or not to match your location.
3. Position the North horizon in the bottom centre of screen. Turn cardinal points on to see ‘N’ indicator.
4. Turn on Alt/Azimuth grid (not RA/Dec equatorial grid).
5. Zoom in or out until the Sun is on the right of screen with N at bottom of screen. The horizon should be slightly curved, (not too much).
6. Turn OFF atmosphere to show a black sky with stars if you like as it makes it easier to see the grid.
7. Increase the time factor to speed up the motion of the sky (just a little until the Sun is moving slowly right to left.
8. When the sun reaches the 0/360 deg azimuth line (true north), pause the time to freeze the movement.
9. Note the time. This is the transit time when the Sun reaches its highest point and is situated on the N-S meridian.
10. Go outside close to this time. When the time is reached the Sun is at transit. Drop a vertical line to the horizon. This is true north. 180 deg in the other direction is true south. I mark the fence in my yard from where I normally place my telescope in the direction of true south.
Of course you don’t need to do steps 1 to 8 if you can simply get the transit time of the Sun either from an app such as Sky Safari (find sun and click on it and it will show transit time), or search the web for transit time (for your location).
Note you can do this at night for transiting stars. Pick stars closer to the horizon and not ones overhead. Even with the Sun this method is easier in winter when the Sun is lower in the sky.
Enjoy your new ‘scope. Try and also learn the sky without the aid of GOTO as it will be more rewarding ultimately as you’ll get to know when and where things are and how they move. You can still rely on GOTO to get you there but I still recommend a chart and manual navigation so you know where ‘there’ is. Stellarium is a great tool for this. And yes join the local society if you like, (subject to any covid requirements). CAS used to meet at Stromlo, perhaps still do.
Here’s my procedure to find True Celestial South using the Shadow method as well -
Finding Celestial True South using Solar Noon ( Shadow ) method ( For Alignment of your Mounts Tripod )
Items needed
1 length of 12mm diameter timber dowel or rod with a 2mm deep hacksaw cut 90 degree criss cross on one end
2 x 3m pieces of 1mm diameter cotton builders string or similar
4 house bricks or pavers or weights
1 x straight edge , ruler or aluminium angle about 500 or 600mm long
1 x fine point permanent marker
1 x Stanley or similar 350mm builders bubble level
1 x PC or laptop with Stellarium down loaded or Smart phone
Location
Your observing location ( approx 2m2 ) or where you will set up your telescope mount should be a reasonably flat or level area with a good view of the sun around midday ( a paved, tiled or concrete ground is preferable) At a remote site you will have to clear the ground of rocks and debris to leave a fairly clear flat area
Procedure
Setting up for your solar noon shadow
Erect timber dowel or rod vertically at your telescope mount location and use the 2 strings to anchor the dowel to the ground like tent guy ropes at north , south , east and west. Use bricks , pavers or weights to hold down the strings tight so dowel sits firm upright. Now use a bubble level vertically against the dowel to ensure it is 90 degrees on all 4 sides N,S,E, W, The hacksaw cuts in the top of the dowel make it easy to make fine adjustments
either way
Finding Solar Noon Time
(Using a Planetarium like Stellarium )
Start your PC or laptop in the morning and open Stellarium
Move your planetarium view to the left or right until you reach the north (N) cardinal point and move up until you see the Sun
Click on the Sun and you will see it’s read out data on the top left of the screen
Now open the Time window and move the time forward until you view the Sun bisecting the north meridian line or until read out data on Az/ Alt degrees goes from 359 degrees to 0 degrees
At that very point and time , record the time from the clock ( eg 12.35pm )This time is your Solar noon time which you will use later
(Finding Solar noon on a website )
Most meteorological websites show solar noon times at or near your location
Marking your Celestial True South Line
Go to your location about 15 minutes before the designated solar noon time with your smart phone , ruler or straight edge and permanent fine tip marker
The timber dowel or rod should be casting a 500mm long thin shadow across the ground towards the south
At exactly solar noon time , mark a line on the ground from the centre base or the timber dowel or rod outward along the exact centre of the shadow to at least 500mm out. Use your ruler or straight edge and be as precise as you can.The more precise you are , the closer you will be to true south and eventually polar alignment.
This line represents the True South line and can now be used again and again when you set up your tripod , mount and telescope
I found the above method of finding True South far more accurate than any compass with magnetic declination or phone app etc....
Just to complete the story we managed a successful alignment tonight. Once aligned targets were acquired in the centre of the field of view. Moon was fantastic and Orion Nebular impressive
Success was achieved using the shadow method
Thank you all very much for the advice and encouragement
Just to complete the story we managed a successful alignment tonight. Once aligned targets were acquired in the centre of the field of view. Moon was fantastic and Orion Nebular impressive
Success was achieved using the shadow method
Thank you all very much for the advice and encouragement
Regards
Geoff
Geoff,
Great to hear your aligned now
Well done !
Martin
Just to complete the story we managed a successful alignment tonight. Once aligned targets were acquired in the centre of the field of view. Moon was fantastic and Orion Nebular impressive
Success was achieved using the shadow method
Thank you all very much for the advice and encouragement
Regards
Geoff
That's great! Alignment is probably the biggest process to master, but it's so good when it works!
