Polar Scope Align for iOS

Polar-scope alignment app for iPhone & iPad.

While this app was made just for myself to allow me to compensate for the centering error of my iOptron polar scope, it was released for the app store when I noticed it was actually more accurate than the other apps available, which either had miscalculations or were not calculating important factors like atmospheric refraction (see the Accuracy paragraph below for more details).
As users appreciated the core functionality, I got numerous requests to support more polar scope types and add more features. I am pleased to say I have satisfied almost all of the requests with support of 18 different reticles covering various types of polar scopes and have added features to assist in any polar alignment situation. The Pro version goes beyond polar-alignment, with weather forecasts, lunar calendars, astro calculators, DSO database and more! So apart from the most accurate polar alignment app, it is now the most complete in scope support and most feature-filled.

App features

  • Wizard to calculate your reticle centering offset and correct or compensate for it.
  • Accurate Polaris / σ Oct position calculation, including atmospheric refraction, stellar aberration, nutation.
  • Automatic Time/Location.
  • Supports a multitude of polar scopes: iOptron, Astro-Physics RAPAS & PASILL, various versions of Takahashi EM-10/11/200/400/500, NJP, PM-1, P2-Z, the latest Orion / Skywatcher, the Classic Skywatcher / Orion / Celestron / Meade / EXOS2 / Bresser, the Telrad, a couple for Astrotrac / Losmandy / Kenko / Avalon, the Vixen Atlux/SX/SXD/SXP/AXD/GP/GP-DX/Polarie Polar Axis Scopes, a Konus and several Polar Finders: Tuthill, Explore Scientific 8×50, Meade 9×60, Vixen Polaris, Celestron 7×50, Carton Optical. PoleMaster help view for South Hemisphere users.
  • Remember zero position on Celestron / Skywatcher / Orion etc reticles.
  • Moon Phase.
  • Deep Space Object Database with Messier, Caldwell catalogs and bright stars (subset of the larger Pro version database).
  • Download and explore DSS color images of the DSO database entries.
  • 6 calculators useful for observing and astrophotography.
  • Full app in red-color night mode.
  • Works on iPhone/iPod/iPad from iOS 7.0.

There is a free ad-supported version simply called “Polar Scope Align” . Extra features of the ad-free “Polar Scope Align Pro”:

  • Ability to manually enter time/date and location (including saving favorites, list of recent locations, loading from world location database, searching online).
  • Zoomable reticle view.
  • Lunar calendar with sun/moon rise/set/twilight times.
  • Alt-az alignment error display for mounts that calculate it after star alignment (e.g. iOptron iEQ45, CEM60).
  • Polar alignment when your scope is not in zero position (for mounts like iOptron ZEQ/CEM on which you can always access the polar scope or trackers like Skywatcher Star Adventurer).
  • Lunar Calendar with solar/lunar rise/set and twilight times.
  • Approximate daytime / no polarscope polar alignment tool. Great for solar imaging (including eclipses).
  • Deep Space Object Database with 13000+ objects from several catalogs (Messier, Caldwell, NGC, IC, Herschell 400, Sharpless 2). The database is searchable and fully configurable with filters, various sorting methods etc.
  • iOptron, NexStar and Meade LX200 Star Lists.
  • Over 20 calculators useful for observing and astrophotography, from eyepiece magnification and field of view, to imaging resolution and reducers.
  • Bubble level (using either gyro or accelerometer) and Compass heading, as well as magnetic declination reading.
  • Special version of Xasteria: World astro-weather report based on 7Timer! data.
  • Water vapor satellite images (Xasteria).
  • List of visible ISS passes and Iridium flares (Xasteria).
  • Switch to alternative night mode colors, or daytime mode for the tools.
  • Red/White/LED light control.
  • GPS accuracy/elevation data.
  • Screen dimming slider.
Download on the App Store

Free Version

Download on the App Store

Pro Version

Watch Edition

Apple Watch Version

Pro Watch Version

The Pro Watch version has all the features of Polar Scope Align Pro, with the addition of an Apple Watch app that offers:
-Graphic & Text display of polar alignment.
-Weather view.
-Bubble level (good for placing the phone on your tripod and looking at your watch while adjusting the legs).
-Day alignment.
-Moon phase/altitude.
-Moon/Sun rise/set/twilight end times.

Some screenshots from the Watch app:

Download on the App Store

Pro Watch Version

Donations

Some people appreciate the continuous development of the app (updates are always free) and ask me for ways to make small donations to show their appreciation. For this reason, there is an in-app option in advanced settings to send a tip (will remove ads from free version), although in that case the app store keeps 30-40% so another option is to use my donate button below (Paypal or credit/debit card):




What’s New

For a list of features added per version visit this page.

Main Screen

Choosing A Reticle

Hit the settings button and choose one of the available reticles. Currently there are 22 choices covering most reticles out there. If you have a different reticle that you would like to see supported, why not send me a photo and I will try to add it.

iOptron

iOptron

iOptron (15-min marking)

iOptron (15-min marking)

Takahashi

Takahashi 1985-2015

Takahashi 2000-2030

Takahashi 2010-2050

Takahashi 2010-2050

Takahashi EM-200/400

Takahashi EM-200/400

Astro-Physics RAPAS

Astro-Physics RAPAS

Vixen Polar Axis Scope

Vixen Polar Axis Scope

Vixen GP

Vixen GP

Telrad

Telrad

Tuthill Precision Polar Scope

Tuthill Precision Polar Scope

Losmandy / Astrotrac / Kenko

Losmandy / Astrotrac / Kenko

Meade 9x60 Polar Viewfinder

Meade 9×60 Polar Viewfinder

Celestron 7×50 Polaris Finder

Vixen Atlux

Orion 2012-2032

Orion / Skywatcher 2012-2032

Classic Skywatcher / Celestron / Meade / Bresser / Orion

skywatcherold

Old Skywatcher / Celestron / EXOS2

Kenko Skymemo RS

Old Celestron CG4/5 / Vixen

Konus 2000-2020

Explore Scientific 8×50 PolarFinder

Aligning Reticle to the RA axis

Before using your polar scope for the very first time, you’d want to make sure its reticle is centered – i.e. aligned with the RA axis. Some mounts might ship with a perfectly aligned reticle, but most do not. It is easier to do the adjustment during the day, so here is a 4-step process which you might have to repeat at least a couple of times until an object stays dead-centered in your polar scope when you rotate around the RA axis. Before starting remove the telescope tube and the counterweights (and for some mounts rotate the DEC axis until you can see through the polar scope).

Polar Alignment Help

Before beginning the polar alignment procedure for your polar scope type you will want to set up your scope with your RA axis points roughly to the Celestial Pole, so that you can see the Pole Star when looking through your polar scope.

The process then varies depending on your mount / polar scope, a brief description for the various types follows.

PLEASE NOTE: The following are instructions from an old version of the app, that can be useful to give you an idea of the process. However, for much improved and up to date instructions always use the “Reticle Instructions” button  in the Settings screen of the app.

iOptron
Takahashi EM-10/11/500, NJP, PM-1, P2-Z
New Synta (Orion / Skywatcher) 2012-2032
Astro-Physics RAPAS

This is the type of reticle the app was originally made for. The difference from other types of polar scopes is that the reticle is not supposed to rotate (in fact the first step to using it is to make sure it is upright), instead software tells you where to position Polaris / σ Oct in its grid. In order to make sure it is perfectly upright, depending on your mount you might have a bubble level near the polar scope that facilitates this, otherwise you will have to level the tripod (with an integrated bubble level if provided) and find the “zero point” of your RA axis (here is how to do that for an iOptron ZEQ25). Unfortunately, Synta (Orion / Sky-watcher / Celestron) mounts do not have the reticle pre-installed at the correct position in respect to the mount. For those, you have to find the reticle zero point by a different method:

You don’t have to repeat the above procedure for every session. If you make sure your mount is always level and the date/time/location correct, starting from Polar Scope Align v2.5 you can press “set zero point” and enter the RA shown on your hand-controller at that instant. Polar Scope Align will then always show you the RA to rotate to using the hand-controller keys to get to the upright reticle position.

After making sure the reticle is upright/level (meaning the 12 hour line is exactly vertical), you simply have to match the app’s pole star position marked with a yellow X to your polar scope view, using the altitude & azimuth adjustment knobs of the mount.

Note that if your reticle has year markings, the Polar Star position might not be exactly where the you would expect it based on these marks. This is normal, as the app calculates the effect of atmospheric refraction for your location and adjusts for more precise polar alignment. See the FAQ entry.

Takahashi EM-200 / 400

Start by setting the offset scale on the RA housing to the value shown on the upper left of the reticle and leveling the reticle (your RA axis should have a bubble level for that). Next, you must match the current time in the inner circle to the reticle’s date circle. Note that you should use your local time zone (as long as it is not more than 15 degrees from your location) minus daylight savings (the time and time zone you should use is shown on the upper left of the app’s reticle for convenience).

After these steps you should have matched the app display and all you have to do is use the altitude & azimuth adjustment knobs to put polaris at the precise location shown on the app.

Note that the Polar Star position might not be exactly where the you would expect it based on the Year marks. This is normal, as the app calculates the effect of atmospheric refraction for your location and adjusts for more precise polar alignment. See the FAQ entry.

“Classic” Skywatcher / Celestron / Meade / Orion / Bresser etc & Older version

The most common reticle is very minimalist (just a small circle denoting polaris and a large denoting its trajectory around the NCP) and found in various mounts from Skywatcher, Celestron, Meade, Orion, Bresser etc. At least Skywatcher and Orion have moved away from this reticle, however for the many people who have them Polar Scope Align gives you the tools to achieve decent precision, even if the reticle is made to be rather approximate. Some very old mounts from the 80s/90s might have a version without the large circle, but just a line featuring a small circle for Polaris and an arcminute scale – those can actually give you a bit extra precision.

Start by turning the RA axis so that the little Polaris circle points exactly down from the center of the reticle. If you want to do it with a precision better than just eyeballing I can suggest a couple of methods:

Now, if your mount has a resettable RA setting circle (e.g. Skywatcher HEQ5), lock the RA axis then loosen the RA setting circle setscrew, set it to zero and tighten. Look at the top left of the app reticle display. Turn the RA axis, using the top scale of the setting circle, to the the “Prev” hour angle shown (or you can use the bottom scale with the “Next” hour angle).However, if your mount has only a digital RA readout (e.g. a Celestron goto mount) or a fixed RA setting circle that you cannot set to zero, then you have to add the “Next” hour angle or deduct the “Prev” hour angle from the RA readout at zero position and move to it. In the below example, if at zero position (Polaris circle pointing down) your Hand Controller (or the RA setting circle) is showing an R.A. of 03h01m and the app reports Prev: 22:40 Next: 01:20, then you add 01:20 to 03:01 (or, a bit harder, deduct 22:40 from 03:01) to find 04:21 and use the R.A. +/- hand controller keys (or manually turn the RA for a non computerized mount) to slew to 04:21 R.A., at which position the reticle pattern rotation should perfectly match what is shown in the app.

The app can help you with the calculation if you wish: Click the “Set zero position” and enter the R.A. at zero position (the 03h 01m in the previous example) press Done and the app will show the “Zero adjusted” reading, to which you can rotate your RA axis. The nice thing about this feature is that if you make sure you always level your mount and have the right time/location (for GoTo mounts), you will only need to “Set zero position” once – the next time going directly to the “Zero adjusted” position should give you the reticle at the correct orientation for alignment without the process of checking whether the reticle is vertical etc. Please not that some mounts may need to be star-aligned at least once before using the “Set zero position” feature in order for the zero position setting to be repeatable.

At this point, for both above cases, your reticle is correctly rotated and all that is left is to use the altitude and azimuth adjustment knobs of the mount to match the Polaris position in your reticle to the app display. You will note that the yellow Polaris position mark on the app might not fall in the Polaris circle. This is because Polaris moves closer to the celestial pole as the years pass, so to improve precision you will have to try and match that movement. If your reticle has an arcminute scale (usually 40′ to 60′), use the top value on the lower left of the app reticle. If your reticle does not have such a scale, you can try to match the app display visually. Note that the app shows an epoch 2000 reticle where the Polaris circle is 44′ from the pole. It is possible that your mount might not be showing epoch 2000 (mine was a bit off), so Polar Scope Align now has a function that allows you to calibrate the epoch of your reticle so that the app will show you the most accurate display possible. To do this, you will have to polar align via another method, preferably drift alignment, otherwise a careful Celestron all-star polar alignment might do it – see the “Calibrate Epoch” function on the settings screen after you have selected the “Classic” reticle.

Please note that the Prev/Next values shown are optimized to give you the best precision, so they include the effect of atmospheric refraction, thus should not be assumed to be exactly indicating the Next or Previous Polaris peak as you might expect (or as you might find in other apps).

Losmandy, Astrotrac, Kenko

This type of reticle is found in the Astrotrac, Kenko Sky Memo and some other mounts like the Losmandy G11. In general this reticle type is not designed to offer the precision of more advanced reticles (the polar scope view is lower magnification), however, Polar Scope Align will improve your precision, especially if your mount has RA axis setting circles (or an RA digital readout).

For the classic Astrotrac, or any mount that does not have RA axis setting circles (or a digital readout), you will have to use the reticle as designed by putting the stars in the specified markers. If you are on a low latitude, Polar Scope Align can help you adjust for the effect of atmospheric refraction. For this, go to Advanced Settings in the app (v2.6+) and enable “Show refraction”. Then align your polar scope as you would with the reticle and then look at the app display:

astrotacscreen

You would have placed Polaris where the orange X mark is located. Using the altitude adjustment move your mount downwards, so  that Polaris moves up (the polar scope is inverted) to where the pinkish cross is located to correct for the refraction effect at your latitude.

For mounts with an RA scale, start by turning the RA axis so that the Polaris points exactly down from the center of the reticle. If you want a method to achieve that more accurately than eyeballing:

Now, if your mount has a resettable RA setting circle (e.g. Skywatcher HEQ5), lock the RA axis then loosen the RA setting circle setscrew, set it to zero and tighten. Look at the top left of the app reticle display. Turn the RA axis, using the top scale of the setting circle, to the the “Prev” hour angle shown (or you can use the bottom scale with the “Next” hour angle).However, if your mount has only a digital RA readout (e.g. a Celestron goto mount) or a fixed RA setting circle that you cannot set to zero, then you have to add the “Next” hour angle or deduct the “Prev” hour angle from the RA readout at zero position and move to it. In the below example, if at zero position (Polaris circle pointing down) your Hand Controller (or the RA setting circle) is showing an R.A. of 03h01m and the app reports Prev: 22:40 Next: 01:20, then you add 01:20 to 03:01 (or, a bit harder, deduct 22:40 from 03:01) to find 04:21 and use the R.A. +/- hand controller keys (or manually turn the RA for a non computerized mount) to slew to 04:21 R.A., at which position the reticle pattern rotation should perfectly match what is shown in the app.

The app can help you with the calculation if you wish: Click the “Set zero position” and enter the R.A. at zero position (the 03h 01m in the previous example) press Done and the app will show the “Zero adjusted” reading, to which you can rotate your RA axis. The nice thing about this feature is that if you make sure you always level your mount and have the right time/location (for GoTo mounts), you will only need to “Set zero position” once – the next time going directly to the “Zero adjusted” position should give you the reticle at the correct orientation for alignment without the process of checking whether the reticle is vertical etc. Please not that some mounts may need to be star-aligned at least once before using the “Set zero position” feature in order for the zero position setting to be repeatable.

At this point all that is left is to use the altitude and azimuth adjustment knobs of the mount to match the Polaris position in your reticle to the app display. Note that you might have a version of the reticle with different year markings for the Polaris line gap, the year number indicated on the lower left of the app reticle should help you with the proper positioning.

Please note that the Prev/Next values shown are optimized to give you the best precision, so they include the effect of atmospheric refraction, thus should not be assumed to be exactly indicating the Next or Previous Polaris peak as you might expect (or as you might find in other apps).

Meade 9×60 RA Polar Viewfinder / Celestron 8×50 Polaris finderscope

This reticle was used on the Meade 9×60 (and the less common 8×50) Right Angle Polar Viewfinder, usually with the 2080 and 2120 fork mounts. It came with a “Polar Reference Circle” card for calculating the position of Polaris for epoch 1975-1995. If you have a straight-through version (not sure if it exists), you’d need to switch to “inverted” in the advanced settings.

Polar Scope Align simply replaces Meade’s Reference Circle, so you follow your manual’s instructions by making sure the Polar Viewfinder is aligned with the telescope tube, then setting the declination to 90 degrees and rotating in RA until one of the cross hairs is exactly vertical to the horizon. Finally, you try to match the Polaris position on the Viewfinder to the Polar Scope Align app display by moving the telescope in altitude (the wedge tilt plate) and azimuth (wedge rotation).

Vixen Polar Axis Scope

Northern Hemisphere: Start by setting the East/West offset (distance from standard time meridian) indicator to the value shown on the upper left of the reticle (turn the eyepiece while holding the date circle). Next, by rotating the eyepiece you match the observing time with the date graduation circle. Note that you should use your local time zone (as long as it is not more than 15 degrees from your location) minus daylight savings (the time and time zone you should use is shown on the upper left of the app’s reticle for convenience). Make sure the Polar scope is level (use the supplied water/bubble level).

After these steps you should have matched the app display and all you have to do is use the altitude & azimuth adjustment knobs to put polaris at the precise location shown on the app. Note that the Polar Star position might not be exactly where the you would expect it based on the Year marks. This is normal, as the app calculates the effect of atmospheric refraction for your location and adjusts for more precise polar alignment. See the FAQ entry.

Southern Hemisphere: The Vixen reticle does not normally offer precision when aligning σ Octantis. However, Polar Scope Align offers a method that should get you to within 2-3′ from perfect polar alignment. All you have to do, is to align the date circle and the time circle on your polar scope exactly the way shown on the app display (while keeping the East/West offset to zero) and make sure it is level using the integrated bubble/water level. Then, you position σ Oct in a way matching the app display as best as you can. You will note that the σ Oct yellow target is probably farther away from the center than the little circle meant for it. This is because apparently the Vixen Polar Axis Scopes sold at least up to the mid-2010’s are drawing σ Oct in the 1995 epoch, when it was closer to the South Celestial Pole, so you should try to match that offset when polar aligning.

Vixen GP/GP-DX

Since the supported Vixen GP reticle is epoch 2000 (which is around the year when Polaris would fall near the center of the little circle – at least for not too low latitudes), you will actually achieve better accuracy by using the “Older Skywatcher / Celestron” reticle available in the app. In that case you will follow that reticle’s instructions which involve finding the position where the Polaris line points exactly down and from this point rotating the RA (using the 24 hour dial as reference) by the amount shown on the top left of the app reticle (“Prev”) – see that reticle’s detailed instructions.

It is still possible to use the Vixen GP polar scope with the original method if you prefer (but only for the Northern Hemisphere). In this case start by setting the time meridian offset scale to the amount towards E or W that the app calculates and shows on the top left of the reticle. Set 0 hour on the RA hour ring to the RA indicator after loosening the setscrew, then re-tighten the setscrew. Unfasten the RA clamp and turn the telescope to match the observing time with the observing date, as shown on the app reticle display. Using your altitude/azimuth adjustment bolts match the Polaris position in your polar scope compared to the Polaris circle, to what the app shows. As noted, Polaris will most likely not be inside the circle.

Telrad

To use the Telrad as a polar finder, apart from aligning the Telrad to your optical tube, you also have to align the optical tube precisely with the RA axis. This might not be easy for a German Equatorial, however for a typical SCT fork-style mount, it involves finding the exact DEC position (theoretically at 90 degrees) where rotating the RA axis rotates your view around the center of your telescope eyepiece (and thus the Telrad, aligned to the telescope). After achieving this, you only use the azimuth and altitude (wedge bolt for fork mounts) controls to put Polaris at the proper position on your Telrad sight, without touching the DEC control.

While you can use the Polar Scope Align display just to get a rough idea of where to put polaris in your sight, you can increase your accuracy by rotating your RA by the amount shown on the upper left (given for both directions) and using the top gap of the Telrad middle circle to better judge the Polaris position.

Tuthill Precision Polar Finder

The Tuthill manuals gave a method to calculate the angle to which you would rotate the sight depending the date/time and location. Since those manuals were using the location of Polaris in the 80’s, they are no longer applicable, but you can rely on Polar Scope Align to give you the correct angle. One problem is that the Tuthill finder was adjusted for a specific epoch, so with Polaris getting closer to the celestial pole as years pass you will be aiming further away from the celestial pole, unless you try to compensate (for reference, Polar Scope Align draws an epoch 1990 sight which might or might not be close to what you have).

It would be possible to adjust your Tuthill to the current epoch. One way to do it without any special equipment requires you to first do a precise drift-alignment of your scope. Once you complete the (not very easy) drift-alignment process, rotate the Tuthill dial to the setting that Polar Scope Align shows at that moment of time and use the adjustment screws (the ones that the manual warns you about touching) to bring Polaris to the center of the cross-hairs. I do not own a Tuthill, so I do not know how easy this procedure is, but in theory it should allow you to adjust your Polar Finder to the current epoch.

Calculating Reticle Centering Error

Going to Settings and hitting “Calculate Polar Scope Reticle Centering Error” will start a wizard which you can follow to both calculate the error and also correct it for more accurate polar alignment. Try to complete the entire process in 2-3 minutes for best results.

Step 1:step1

Position the polar star where the display shows you in your Polar Scope reticle by adjusting your mount’s alt-az controls. Try to be as precise as possible. Press Next > on the app.

Step 2:step2

Rotate your RA axis exactly 90° counter clock-wise (as you are looking towards the Pole), so that the reticle line that was horizontal and pointing to the right, now points upwards. Swipe your finger on the app reticle area and move the dashed cross so that it centers to where you currently see the polar star in your reticle. Try to be as accurate as possible, but don’t take too long – you don’t want the polar star to have moved much in the meantime. Hit Next >.

Step 3:step3

Rotate your RA axis exactly 180°. You should now be 90° clock-wise from the original position, so that the reticle line that was horizontal and pointing left is now pointing upwards. Move the dashed cross again so that it targets where the polar star shows up in your reticle. Again be as accurate and quick as possible. Hit Next >.

Step 4:step4

The app will have calculated your centering error. If it is more than 1.5 arcminutes, a correction will show up as a dashed cross. Return your RA axis in its original position. You now have two options.

If your reticle can be easily adjusted: Use your mount’s Alt-Az controls to position the polar star in your reticle exactly where the center of the dashed cross would indicate. Then use your polar scope reticle adjustment screws to move the polar star to where the regular calculated position (marked by an orange X) would be. You can re-run the wizard to verify you no longer have a centering error.

If your reticle cannot be easily adjusted (e.g. iOptron ZEQ25): After hitting “Done” to accept the correction, your app reticle display will always have a “corrected” dashed cross. Just use this as your polar star target for polar alignment instead of the regular (orange “X”) mark, to compensate for your centering error.

Xasteria Weather Report

Polar Scope Align Pro contains a version of the free Xasteria World Weather Report, with the addition of the ability to switch to night-mode (with a dimmer as well like the rest of the app) and the support of the location manager with the ability to search for locations (online or offline) and save them as favorites. For more information about the weather report, see the Xasteria page.

Deep Space Object Database

The DSO Database contains over 13000 objects from several catalogs in the PRO version, while it has the Messier and Caldwell catalogs for the non-pro versions. You can filter the list by catalog, object type, position, brightness etc and sort them any way you like.

Filters / Sorting

Several filters are available to hide objects that are of no interest. For example, limiting altitude to 0 degrees will only show objects that are over the horizon at that moment (or you might want to use something like 15-20 degrees since objects too low don’t make great targets). You can limit by minimum magnitude, brightness and angular size, however be aware that this type of data is not available for all objects. For example, surface brightness is available mainly for galaxies, to still show the rest of the objects when you are filtering by minimum surface brightness use the “Show when missing data” option.

Various sorting options are also available, which can be applied in either ascending or descending order. Note that you can sort objects by distance from a specific object – just go to the object list, click to show details of an object and hit the sort button. You can reverse the order to descending distance, if you go back to the sorting configuration screen and click the “Descending” button.

 Settings

You can choose whether to prefer arcmin (‘) or arcsec (“) to be shown, as well as whether you want equatorial coordinates or alt-az in the list view.

Data sources

Multiple sources have been combined and cross-checked as much as possible for the DSO database. Among them: Dr. Wolfgang Steinicke’s Revised NGC/IC (with permission), Saguaro Astronomy Club, SIMBAD, VizieR, Courtney Seligman’s Celestian Atlas, Sloan Digital Sky Survey and more.

Calculators


Over 20 calculators are available (for the Pro versions), split in three categories, depending whether they are more useful for observing, imaging or other applications. The calculators always remember your last entries, and their order can be rearranged at will, so that you can easily find your favorites. The list can also be filtered by calculator type using the buttons on the top. The list of calculators at the release of version 4.4 was:

  • Eyepiece Magnification
  • Eyepiece Field of View
  • Eyepiece Exit Pupil
  • Maximum Field of View
  • Telescope f/ratio
  • Eyepiece Projection Focal Length
  • Field of View for Imaging System
  • Resolution (arcsec/px) & focal length for Imaging System
  • Focal Length and Object Size
  • Focal Reducer Reduction
  • Focal Reducer In-Focus
  • F/ratio ~ Brightness/Exposure increase
  • Brightness ratio from Magnitude
  • Julian Date
  • Hour Angle ~ Degrees Converter
  • Equatorial Coordinates ~ Alt-Azimuth Coordinates
  • Frame rate ~ Exposure
  • Parsecs ~ Light Years Converter
  • Light Years ~ Miles/Km Converter
  • Lunar Feature Image Size
  • Actual size of lunar view
  • % Speed of light ~ miles/km per sec
  • Special relativity time dilation
  • Solar Feature Size
  • Telescope Light Gathering
  • DSLR Exposure
  • Telescope Limiting Magnitude
  • Equatorial – Ecliptic Coordinates
  • General Relativity Time dilation
  • Fahrenheit – Celsius

Daytime Polar Alignment

Polar scope Align Pro assists you in daylight polar alignment, useful for solar observing / eclipses, or also for night-time alignment where you don’t have a line of sight to the polar star. See details in this blog post.

Accuracy

Polar Scope Align is designed to be accurate within a few arcseconds. If you want to check its accuracy, you can select the Astro-Physics RAPAS reticle which is upright and has an Hour Angle measurement format similar to planetarium software and check the result against a good such software like Stellarium or Cartes du ciel. In fact, Polar Scope Align is a bit more accurate than old versions of Stellarium (the difference is less than 20 arcsec, so barely visible in a polar scope), as it includes stellar aberration and nutation calculations, so you’d have to disable them from Advanced Settings to precisely match e.g. Stellarium 0.13.3. Example comparison screenshot with Polar Scope Align’s Hour Angle within 5 seconds of Stellarium (make sure you have enabled “atmosphere in Stellarium settings):

Polar Scope Align vs Stellarium (click to enlarge)

Polar Scope Align vs Stellarium 0.13.3 (click to enlarge)

This does not mean that you can find many other sources agreeing with Polar Scope Align and Stellarium*. Most apps in my experience have either significant errors in their calculations, or disregard atmospheric refraction (or both). Another accurate and popular planetarium program is Cartes du Ciel, which actually includes aberration and nutation in the Polaris hour angle, but does not include refraction. This means that when you select apparent coordinates in CdC and enable aberration and nutation but disable refraction in Polar Scope Align, you can match the hour angle within a couple of seconds. Also, Polar Scope Align matches the transit times calculated by the US Naval Office, so you can cross-check with that.

* Strangely, newer Stellarium versions (0.15+) have changed their calculations and now can be up to a minute off compared to Polar Scope Align. As PS Align matches the USNO transit times and Stellarium no longer does, I am not very worried about the discrepancy. Plus, the difference with current Stellarium is so small that it is not actually visible in a Polar Scope.

FAQ

  • Will there be an Android version?

My own main phone is an Android, so I’d like to do an Android version at some point. However due to my regular job it was much easier for me to work on iOS where I had development experience – I’ve never worked with Android or similar. Hence I’d need to find quite some spare time to do it and that seems quite unlikely for the near future. Sorry.

  • Why doesn’t the bubble level or the daytime alignment work (I get no heading)? (Pro only)

Go to your deviceSettings -> Privacy -> Location Services. Make sure Location services is On, that Polar Scope Align Pro is listed as “While Using” (i.e. it is authorized to use your location) and then scroll down and go at the bottom to “System Services” and see if anything (esp. if it seems important) is disabled (e.g. compass calibration, share my location).

  • How to zoom the eyepiece reticle view? (Pro only)

If you have the Pro version you can click the magnifier button on the bottom of the display which will zoom into the polar star position and let you further zoom in and out with the traditional pinch/pull gestures.

  • Why is the date off by one day?

Up to version 2.6 the main date/time fields are in Universal Time, so if you are not on the GMT time zone, your time zone date and the UTC date can be different for a few hours per day (e.g. if you are on EST, the app will switch to the next calendar date 5 hours earlier than your local time zone). This was by design, since setting up a scope in UTC can avoid confusion about time zones, DST etc. especially when you travel, and it was my own preference (I made the app just for me originally). From version 2.7 the app shows local time/date by default, with UTC shown under LST (and a day offset next to it). If you prefer the old style with a UTC main display you can still go to Setting->Advanced Settings and enable “Date/time in UTC”.

  • What is “Force GPS”?

Normally, iPhone apps rely on iOS’s radio-based location services which save battery and so does Polar Scope Align. However, if you travel to a rural area with no nearby cell coverage, you might want to turn on the GPS satellite location service for a while, which is what the “Force GPS” option will do.

Example of corrected Polaris location for a latitude of 25° (e.g. Florida) for some time in 2015. Note this is an upright Astrophysics RAPAS reticle.

Example of corrected Polaris location for a latitude of 25° (e.g. Florida) for some time in 2015. Note this is an upright Astrophysics RAPAS reticle.

  • Why is Polaris/σ Oct not moving in a perfect circle according to the app? / My reticle has “2010-2040” circle markings, why does the app deviate from those? / Why is the position I get with Polar Scope Align different from some other apps?

The lower a star is in the horizon, the more it will be affected by atmospheric refraction. The phenomenon is due to the air density variations that the light from the star goes through before reaching you and has the effect of making the star appear higher than it really is. If you are at a latitude of more than around 45° the refraction is less than an arcminute, so you are not to worry about it. However, at lower latitudes it should be taken into consideration for accurate polar alignment, as it can reach up to 35 arcminutes near the equator. Some software do not do this calculation so they will give you slightly different results than Polar Scope Align, with the polar star always on a perfect circle around the celestial pole. See on the right an example for someone observing from a latitude of 25°, with the white circle denoting Polaris’ location throughout the day showing an upwards offset (for a common straight-through polar scope the offset would be downwards). So, even thought it is 2015 you might have to align by putting Polaris on the 2010 or the 2020 circle depending the time of day (or even further for lower still latitudes). See also the “Accuracy” chapter above.

  • Would the white light (i.e. white screen) on an iPad be a good idea for flat frames on smaller aperture scopes like refractors? (Pro only)

Yes! This is of course a “trick” FAQ, in the sense I don’t expect it to be a frequent question, but I wanted to note the reason I added the color slider for the (originally just red) light. So, when I want to take flats with my 80ED, I use the app on an iPad and switch on the red light, turning it to white and putting the iPad in front of my front aperture. More elegant than my previous method of having a white .jpeg photo open in an image viewer 😉

  • What is the difference between accelerometer and gyro for the bubble level? (Pro only)

Newer phones have a gyro in addition to the accelerometer, which should be more precise, so you should leave the setting at “gyro”. However, I have had phones where the gyro failed (along with the WiFi on an iPhone 4S), so this option is a sort of “backup” for those cases.

  • Is the compass accurate? Does it show true or magnetic North? (Pro only)

The magnetometer on all phones often requires calibration to perform accurately. To make sure you are getting an accurate reading, try waving your phone in a figure “8”. I have to warn you though that the accuracy of digital compasses varies significantly – I have found that it is usually better on newer iPhones than iPads for example, and in general a “classic” physical compass will be more accurate (as long as you apply the magnetic declination correction correction to the magnetic North heading of the compass). The compass in the bubble level automatically applies the correction and points towards the true North.

  • I am using a polar scope that you don’t support. Can you add it?

I probably can. Contact me with details, images etc.

  • What is the rotate icon for? (Pro only)

For mounts on which the Polar Scope view is always unobstructed (e.g. iOptron ZEQ25, CEM60 and also trackers like the Sky-watcher Star Adventurer), you can check to make sure your polar alignment is correct, while you are tracking an object. E.g. if I bump my scope a bit or the tracking seems a bit off in general, I can verify with a quick look through the polar scope, without even going back to the home position. Also, if you have a heavy scope on a light mount (as it is the case with my C9.25 on my iOptron ZEQ25) it is possible that there is some flexure that affects the polar alignment when the scope moves to a target. By correcting the polar alignment once you are on your target with Polar Scope Align Pro you can achieve longer unguided exposures in these situations.

  • Do you recommend a specific iOS version and/or specific device?

Polar Scope Align works on iOS 7 and up (iOS 9 for the Watch Version) and I do try to test with many iOS versions, so iOS version should not matter much. As for the actual device, the non-Pro version of Polar Scope Align that does not have a zoom screen is much easier to use on an iPad. The Pro version with the zoom view is great on an iPhone too, but the smaller-screen iPhones do look rather cramped. Also note that the wifi-only iPads lack a GPS radio receiver, so if you plan to use the app far from cell phone towers you’d need an iPhone or a wifi+cellular iPad. Also, the iPod Touch lacks the GPS received and also gyro and magnetometer (digital compass), so some Pro functionality that depends on it will not be available.

  • How accurate does my location have to be?

It doesn’t have to be very accurate, within a few km is fine, as Polar Scopes are not more accurate than that. The more important issues are the correct centering of your polar scope reticle and having an app such as Polar Scope Align that does a good job of calculating the position of the Polar star.

  • Why are there only 3 polar scope types (Inverted, Right Angle, Correct) in the Advanced Settings screen? 

You might have seen independent flip horizontal/flip vertical controls on other apps which give you 4 combinations of polar scope types based on their viewing type. Polar Scope Align only shows the 3 combinations that are actually possible in a polar scope, although the vast majority of polar scopes just has a 180 degree rotated view, or “Inverted” like looking through a straight-through refractor. In fact, when you select a reticle, the reticle-type is auto-selected so you should not change this unless you have a pretty non-standard configuration.

  • What does refracted north / true north polar alignment mean? What’s the difference?hy are there only 3 polar scope types (Inverted, Right Angle, Correct) in the Advanced Settings screen?

If refraction calculation is enabled in advanced settings, your polar alignment will be to the true celestial pole, i.e. the actual point in the sky the earth axis points to. If you disable atmospheric refraction calculation, your RA axis will be pointing to the refracted pole, which is where the celestial pole seems to be after the atmosphere has bent the light coming from it. For objects high in the sky, which is what we usually target, an alignment to the true north will provide better tracking, especially in now latitudes – hence that is the default behavior. However, if we are aiming at relatively low targets which themselves are subject to refraction, it is possible that an alignment to the refracted pole (i.e. disabling refraction calculation) might perform better for those target.

  • What is Clay’s Kochab Clock?

If you click on the underlined name of the polar star on the main screen, you will get extended info on the star. Among this info, there are 4 times that mark when the polar star will be exactly N, E, S, W of the celestial pole. Clay’s Kochab Clock is an alignment method which uses the fact that the North Celestial Pole, Polaris and the star Kochab are along pretty much a straight line. While that method is not as accurate as what Polar Scope Align normally attempts, inspired from that method the four times that can provide the easiest alignment for some mounts lacking RA grading/setting circles are listed. At the times listed for polaris directly N/S of the NCP, you center your polar scope on Polaris then use only the vertical controls of your mount to bring it to where the app display shows. Similar for the E/W times, you only use your horizontal controls. Of course this requires your tripod to be level, but takes the rotation of the reticle out of the equation. Also, this can be applied to South hemisphere alignment (unlike the full Kochab method).

  • Why doesn’t the app always rotate to landscape?

The interface was built to take advantage even the smallest screen and was optimized for portrait mode, so it will not fit an iPhone landscape mode. Hence, landscape is only available for iPads – and that only for the Pro version, as landscape mode is only really helpfull for Pro tools like Xasteria. Furthermore, the Bubble Level and the Daytime Alignment tool would be disruptive if they changed orientation while you were using them, so they are always portrait-mode. Lastly, the Settings screen requires a redesign to fit even on an iPad landscape view, which is so far not a priority.

  • Why are some NGC/IC missing from the DSO database? Why do some NGC/IC objects have “A, B, C” or “-1, -2” variants? (Pro only)

The original NGC/IC catalogs contained many errors when they were created (non-existent objects, duplicates etc). These have been addressed as best as possible. Objects that were listed but cannot be found do not appear on the DB. Objects that were listed more than one time get a single entry. Some objects are actually more than one, e.g. 2 galaxies that were thought to be a single one, these get a separate entry with a suffix. Also, included for completion, are some objects that should not really be in the catalog, as they were not actually seen when the catalog was compiled, but due to proximity/association commonly listed with an NGC number and a letter appended.

  • Why are there 399 “Herschel 400” objects? (Pro only)

Herschel catalogued a planetary nebula as two separate objects, so NGC2371 and NGC2372 are properly shown as a single nebula in the database and these two Herschel objects count as one.

Also: Xasteria FAQ

Data Share Policy

From version 3.5, after an upgrade of an existing app installation, Polar Scope Align will report the iOS version, and basic app stats about which reticle and which tools were used from the previous version. This data is of course completely anonymous and will not be shared (unless I make something like a pie chart to share with people), but will help me decide which features I should work on. The original reason for this report is to see whether there are iOS 6/7 users, as supporting those old iOS versions requires extra work.

Support

If you have any questions or problems with your app, the quickest solution is to use the Contact page to write directly to the developer. Or you can post your suggestions, questions in the comments below

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