Different Time Definitions 

UTC ("Universal Time Coordinated") is a time scale derived from TAI but adjusted with leap seconds in coordination (thus the "c") with UT1. In other words, UTC is designed to keep an, essentially, unvarying atomic time scale (TAI ) relevant to an imperfectly rotating Earth (measured by UT1).



TAI ("International Atomic Time") is a time scale based on an international ensemble of atomic clocks.



UT1 ("Universal Time One") is an astronomy-based time scale traditionally derived by combining UT0 observations collected from worldwide locations.



UT0 (“Universal Time Zero”) is a geographically local, astronomically measured, time scale.



GMT ("Greenwich Mean Time") is a version of UT0 as traditionally measured from Greenwich, England. Leap seconds are irrelevant to true GMT because GMT is astronomically derived.



GPS Time is an atomic-based time scale maintained by the U.S. Naval Observatory. Commonly, GPS receivers convert "GPS Time" to UTC by means of additional information encoded in the signal stream.



Culturally:



UTC is the modern equivalent of GMT in that it presents a worldwide and not-seasonally-changing time stream. They are encoded in the same format.



UTC and GMT differ by, practically, nothing. Moreover, many organizations, such as the BBC, which claim to report GMT are actually reporting time derived from an encoded radio or GPS source. In other words, they report UTC - sometimes even UTC derived from GPS Time.

Pixinsight-Part 1 (Blink & SubFrame)

After using Photoshop for some years I always had this urge to try Pixinsight, as I always say, you learn something new everyday, and who knows I might develop my processing and advance further, I am not sure where I am going or what I will achieve, but whatever I lean or not I will recorded each step on the way.

When I open SI and I see all the different processing tools under 'All Process' and those under 'Scrip' and the first impression is wow, where do I start??, while in Photoshop, the frames are coming over already  calibrated (from third party software like PhotoStack2), in SI you have the option to do the calibration as well, or used a third party software to carryout this task and just concentrate on the processing the frame in PI, so this addition of extra menus its a bit intimating.
.
First before I start this adventure I will start off by describing the meaning of 'Image Scale' followed by some useful points about PI , why?, because this awareness will come handy later.

1.    Image Scale 

arcsec/pix=(pix size/focal length)*206.3

Is the angular area of each pixel can see, this is referred as 1 bin, so if we combine 4 pixels into a single pixel the are will increase by 4x = 2bin.

First Setup

A camera / telescope combination. Telescope with 106mm aperture and 530 focal length, this means a F5 (530/106). The camera chip 2750 x 2200 with 4.54 pixel size. The image scale of the pixel is 1.76 arcsecond/pixel and the field of view is of 80.98 x 64.79 arcmin

 Second Setup

Telescope 356mm FL is 2563mm therefore F7.2 will result of an Image Scale of 0.72 arcsec/pixel and Field of View of 48 x 33 arcmin with an FOV in degrees of 0.8.

So the best resolution of both combo is the latter with a 0.72 arcsec/pixel

2.  Loading an Image

When loading an image in PI in 32 bits, the computer will display it in 8 bits, do not reduce from 32bits to 8bit the images. Instead use the STF (Screen Transfer Function) to stretch the images to see it better on the computer screen.

3.   PI is divided into two main sections for processing.

On one side we have the Process and on the other the Scrip. In Process you can find all the tools provided by PI, and in Scrip are third parties software within PI developed by PI users.

4.   On the top screen modules/menus

On the top selections we have : File-Edit-View-Preview-Mask-Process-Script-Workspace-Window-Resources and if you scroll down there are quite a bit of extra menus.

We will skip these menus for now.

5.   Inside PI (whole)

The software is divided into 4 sections - Preprocessing, Linear Post Preprocessing, Nonlinear Post-processing and Special Processing

Part 1

Pre-Processing

The processing of an image can be achieved by using the processing tools, if you click on the 'Process' and then <all process> you will open the screen below.

After a night of imaging you are exacting but also aware that not all the frames would be use for calibration for different reasons, previewing them can be achieved in PixInsight. Most processes can take quite a bit of trial and error to get the right settings and fine tune them for the optimal result. We run these processes on previews so that it is much faster to see the effects compared to running it on the complete picture. Furthermore, we can use multiple copies of the same preview and apply the process with different settings so we can really compare the results of our fine tuning in great detail.

One of tools that unable preview your frames is 'Blink', it will preview a set of images. Open the images with the small folder in the Blink dialog window.

This tool will be part my of image-processing workflow, which lets me inspect each image and discard any that appear to be of poor quality (images with clouds, poor tracking, and so on). PixInsight’s SubframeSelector script (Script > Batch Processing > SubframeSelector) can automatically evaluate images and sort them into “approved” or “rejected” groups using quality criteria you can modify. When evaluating image quality, I will use this opportunity to identify the best one to use as a reference when aligning images.

Preselection frames

1.      Open the  Blink  tool in the Process Explorer (vertical tabs);

2.      Select  the light subs in the  Blink tool;

3.      Press the "play" button and check if you see streaks of satellites, planes or meteorites;

4.      If stripe formation is visible, it is usually located in one subframe, write down the name of the sub in order to have it removed in the subsequent steps or remove all the file physically by 
removing the 'X' to mark it as bad.

5.     Its important that you keep those good-looking images and have adequate number of good                  images.
6.     Thinking about those poor images, I believe it will be a good idea to create a new folder (give it a name that you know they junk images).

The following Video will help you to understand better the process

SubframeSelector script

After calibrating  we could immediately jump to registration (aligning the images).  However, there’s another tool in the PixInsight called SubframeSelector that can help to enhance your results if we use it before registering our data.  The originatly the SubframeSelector was  to identify light frames that might have errors that were severe enough to exclude them in your final stack.  This could be from a cloud passing through the field of view, a piece of grit sticking in your gears and throwing off your tracking, focus slipping, etc.  It also supports the ability to add a keyword into the FITs header that can be used by ImageIntegration later on to weight how the images are combined (but this is another story).  This is exceptionally useful if you have data from multiple sessions or instruments where the SNR or resolution my vary considerably due again to the elements mentioned above.  By weighting images you can control how much influence an sub frame with a lower SNR has on the final integrated image.

First step is to select the images then move to opening it inside SFS (see below), Under System Parameters, enter the image scale of your telescope (use the formula I mentioned above)  and camera in arcseconds per pixel and other pertinent information.

If your are setting the Star Detection and Fitting and these settings are inadequate, the console will report failure, leave the setting as default it works perfectly, but before hitting the  measure button, if you feel that you can enter a formula into Expressions/Approval to automate the grading process, do so, if not do not worry. Finally click measure, and the  Process Console   will appear as the script does its calculations.

Tables

The Table at the bottom , shows the finding calculation Note, you can change the field of interest, three of the main and basically used by many astrophotography are: the images’ signal to noise  ratios  , choose SNRWeight (noise), and in descending, if the SNR reading is higher-this is a good thing. 

If your choose on the Full Width at Half Maximum (FWHM) of the stars in the images, remember if the file at the top of the list would have the highest FWHM value—this is a bad thing. You might therefore switch to ascending order, placing the file with the smallest/best FWHM on top to make that category easier to read. 

FWHM measures star size/spread whereas eccentricity measures shape in terms of how out of round the star are.

Formula into Expressions/Approval 

Limits -Minimum and Maximum settings 

Eccentricity 

For eccentricity <=0.4 is considered 'round', if anything  from 0.4 to 0.49 will be acceptable,  if generally stack anything <0.55 and  above 0.55 and start to get picky and choose, it all depends how many frames you have to play with. For example if they're mostly 0.4 to 0.5 you can select with assurance and toss away any outliers that are above that, I would reject anything above 0.6.

FWHM

FWHM is a lot harder to be so absolute about, as it largely a factor of the seeing. On a really good night a seeing <3", but a 5" is considered poor. As such, for FWHM I tend to work in relative terms within the available frames I have for a target rather than absolutes. FWHMSigma is a good approval term to use for this and I'll typical approve frames that lie within 2 sigma, so an approval term of FWHMSigma < 2.

To sum up a typical approval expression I'll use for these factors in SubframeSelector will be:
Eccentricity < 0.5 && FWHMSigma < 2


[What I am saying here is I will only accept those frames with FWHS that lies with 2" and Eccentricity with a 0.5 value or below, any frame above any of these two parameters will be automatically rejected.]

• Smaller FWHM values are better.  I’ve also restricted the list by the Eccentricity and Noise metrics.  
• Noise is fairly straight forward, the higher the noise level the more difficult it is to discern your target, so again, lower values are better.  
• Eccentricity is a measure of how far from round a star is.  If a star is very elongated it will have a higher Eccentricity value, so it is also better to have lower values here.

The weighting is more complicated. Basically its means that you need to use one of the three weighting (SNR-FWHM or ECCEN). When applying the weighting to one of the three, first it will be based upon it own parameters--if you use FWHM as your most important factor to build the expression. If Eccentricity is more important to you than FWHM you can change the weightings in the formula.  

If we take the expression below (provided by....) and we take my reading below under FWHM its ranges from 3.05 to 3.6, so I  want to use a maximum value of 3.05 (<3.05) not further then this, so I put in the first part of the expression (3.6-3.05). For the Eccentricity range 0.534 to 0.511, and for the Noise its 0.736 to 0.707.

The numbers in front of each factor is based on 50 (50 frames), if you are interested in having a good FWHM (better resolution to rounded stars) you will have a higher value (30) in front of the equation. This is what the 30, 5 & 15 values are for.  If you were less concerned with resolution and wanted rounder stars with a better SNR then you might weight FWHM lower and Eccentricity and Noise higher.
 
            Most important                          Second most important                     lease important
(30*(1-(3.6-3.05)/(3.60-3.05)) + 5*(1-(0.534-0.511)/(0.534-0.511)) + 15*(1-(0.736-0.707)/(0.736-0.707)))

This expression will be reduced to:

(30x(1-(1))+5x(1-(1))+15x(1-(1)) = 30+5+15=50

If you need a spreadsheet to help you out in the expression, I found this easy way out to expressions in the following website:

Expressions formula in Excel (click here)



Preprocessing Flow

When preprocessing images, we follow a subset of these steps (depending on the reqirements of the data):

1.       Image Calibration (use Pixinsight’s ImageCalibration process to apply super bias, master dark and master flat; perform RBI mitigation if necessary)

2.       Blink Selection (use PixInsight’s Blink process to quickly identify and eliminate out of focus, low contrast, or otherwise poor frames; this is also a good time to review the effectiveness of calibration on each sub)

3.       Cosmetic Correction (use Pixinsight’s CosmeticCorrection process to remove hot pixels, cold pixels and defective sensor columns)

4.       Subframe Selection (use PixInsight’s SubframeSelector script to measure quality of each sub, eliminate outliers, and apply a quality weighting value to each sub based on FWHM, Eccentricity and SNRWeight factors; also to note the highest quality sub for each filter for use during local normalization)

5.       Image Registration (use PixInsight’s StarAlignment process, including drizzle data if desired)

6.       Local Normalization (use PixInsight’s LocalNormalization process for including localized contrast data; improves signal to noise ratio and results in cleaner background transitions after integration)

7.       Image Integration (use PixInsight’s ImageIntegration process, applying quality weighting and local normalization data from earlier steps, and updating drizzle data if desired)

8.       Drizzle Integration (use PixInsight’s DrizzleIntegration process if desired, applying local normalization data from earlier steps)

9.       Dynamic Crop (remove any black edges due to tracking movement during imaging; applies an exact duplicate crop to each of our stacks so that our registration remains intact)

 Part 2

SGP - Image Capture Software

For anyone looking for image capture software - SGP is one great package, although for me CCDAP still my favorite, its compatible with TheSkyX, and Maxim DL making it a excellent imaging capture team difficult to beat, true you need to spend good money compare to SGP.

 SGP has developed over the past couple of years, easy to use and for a beginner you can developed your skills using it as it has grown. (The developers are very active on the forum - answering questions and taking suggestions on board).

SGP like CCDAP is compatible with other astronomy software like PHD2 for guiding (if you need to guide), with Astromi for Model-Creator or Model Maker for modelling the sky and MBox  for GPS and temperature control, all excellent software that works perfectly with 10Micron mounts, a mount which is top in my list for amateur astrophotographers.

The mount of course needs good polar alignment as always but I do not have to align on any stars - plate solving tells the scope exactly where it is pointing. When it reaches the meridian - the scope will flip guided by this software and resume on the other side without any input from me at the time of flip. It works in tandem with PHD2 guiding software and as well as when not using guiding scope only with the sky modelling.

I  recommend this combination for anyone wanting to control your astro-image capturing, I have mentioned above the mountl, It also controls the camera (obviously) and the filter wheel (if used) along with the focuser (again if you have a PC controllable set-up)......along with a couple of other things.

I don,t think you can go wrong with SGP for the money, like you can't go wrong with Pixinsight or PS for post processing for the money you pay for them. You should buy software and  learn to use it and resist the temptation to buy something "else" unless there is a specific capability that you cannot get with what you already have - say "mutliple targets". Knowing how a package works will outweigh anything else over time, and  it's for this reason that I prefer CCDAP over SGP.

 I use MaximDL all the time without serious problems. In last years I have had exactly few problem that had me flummoxed and cost me imaging time, but what program is free from it.

 I've used CCDAP, MDL with TheSkyX it with a 250 Tak and the 106ed,  It works fine with my SX694 and FLI16 and the Moravian 11000, my 10Micron Mount, my AP 11000. It gives me a vast array of different capabilities to examine the data I am collecting, QA it, stack it and due on the fly digital development. It handles meridian flips, has auto shutdown capabilities, etc etec. I have NEVER seen a "guide star" problem when the guide star was present in the sub frame. I have seen hot pixels a lot though and very few people who understand how to handle them. It could use better hot pixel detection for the MDL.

10 Micron 1000 Mount

The mount is mechanically looks stable, the instrument payload capacity is 25 kg, my equipment will not surpass this weight, so I am confident that it will preform well.  The electronics is placed in an removable, independent control box, which is quite handy as it can be fixed if necessary without touching the mount. The GM1000 HPS can be controlled by using the hand pad without any connecting to an external PC, this is actually better them my other mount the AS1100gto,  also, the mount can be controlled by using common software by connecting it to a PC via RS-232 serial port, Ethernet or WiFi. I personally prefer the Ethernet connection.
The object data base contains a lot of different star catalogues and deep-sky-objects up to the 16th magnitude. It is possible to load orbital elements of comets, asteroids and artificial satellites. HPS stands for High Precision and Speed. With the help of ultra-high resolution absolute-encoders, directly mounted at the right ascension and declination axis, the 10micron GM1000 HPS allows a very accurate tracking.


For the standard alignment I have taken the following procedure before using an external pointing model like for example, Model Creator.


Quick setup and alignment checklist (GM1000HPS)

1. Disassemble the base adapter from the mount unscrewing the four knobs.

2. If you have a Baader AHT or 10Micron 30H100 by Geoptik tripod, assemble the tripod adapter on the tripod.

3. Mount the base adapter on the pier/tripod, paying attention that the protruding block is

southward if you are in the northern hemisphere, northward if you are in the southern hemisphere.

4. Put and lock the mount on the base adapter.

5. Adjust the altitude of the R.A. Axis to match roughly the latitude of your observing site.

6. Mount the counterweights and the telescope OTA.

7. Turn on the mount.

8. Balance the telescope following the procedure detailed in the manual.

9. Check that the observing site coordinates and time are correct. You can use an optional GPS

module to obtain these data.

10. Clear the previous alignment using the Alignment→Clear align function from the menu.

11. Choose from the MENU: Alignment→ 3-Stars.

12. Choose one star from the list and press ENTER.

13. Press ENTER to confirm the slew to the star; then centre the star with the maximum

precision (a high-magnification eyepiece on your main scope, without diagonal mirrors, is

preferable) and press ENTER again.

14. Repeat steps 12. and 13. for two other stars.

15. At this point, the mount will point correctly, but if you plan to do any photographic

observation, you need to adjust the polar axis position. Choose from the menu:

Alignment→Polar Align and select a star from the list.

16. The system will ask to slew to the star. Press ENTER to confirm. The scope will miss the

star. At this point DO NOT centre the star with the keypad; use instead the altitude and

azimuth mechanical adjustments until the star is centred. Then press ENTER.

17. Do another 3-Stars alignment by repeating steps 10. to 14..

18. If you like to have a better pointing and tracking precision, select from the menu:

Alignment→Refine 2-stars to add stars to the pointing model (up to 25 stars in total can be

used). Note: for the best result it's necessary to use more then 10 stars.

19. You can check the orthogonality error and polar axis alignment error by selecting from the

menu Alignment→Align Info. Note that orthogonally error does not affect the pointing

precision or tracking.

The above quick standard polar alignment is reached by aligning the mount to the north aligning on three stars. By adding more alignment stars the model is refined. An estimate of the expected pointing accuracy is shown on the hand controller after each additional calibration star is inserted.




The usage of a pointing model up to 100 stars allows the correction of the classical polar alignment and conic errors, also the most important flexure terms of the telescope. With the help of a good pointing model it is possible to obtain a pointing accuracy of 20 arcseconds RMS.


10 Micron GM 1000 HPS take three stars and have an ability to do a high quality polar alignment. It normally takes about 15-18 stars on the GM 1000 HPS to generated a polar alignment of 30 or so arc seconds accuracy. After an observing session, the entire electronics box (motor electronics with Linux computer) and HC can be easily detached and protected from premature aging and moisture damage, especially in winter weather.


A virtual key-pad on PC is available for remote control.

An example of Model Creator, the mark is created by you after setting up all the parameters related to Mount, Telescope and Focus length

Part two of the process is to do a selection of targets/points whereby this will be used by the mount and create a  map of your sky, meaning that the mount will know exactly where you are located in the sky.

Building the Garden Shed Observatory

The garden shed amateur observatory is coming along, really I haven't much time for astrophotography while changing to new a house in Spain with a garden and an improvement of night sky.

First Construction 

Add caption

Part 2

Shed Build and rolling roof

Parts 3

Installing the internal red light, an extractor to reduce the internal temperature in the summer, alignment of the AP 1100GTO with the Polar Star, and the installation of a DC to AC convertor from 230v to 12v with a maxim ampage of 20.

Polar Alignment of the mount

Red Light behind

Right Angle Scope for Palr Alignment

AC to DC convertor

Focus Convergence -Focusmax

After creating the  V-curves in FocusMax and want to enable the focus convergence., but first we need to calculate the Critical Focus Zone (CFZ) and translate that into focuser steps.

CFZ for a scope can be worked out with this fomula:

CFZ(in Microns) = 2.2 x (Scope_Focal_Ratio²)

My Telescope is a Takahahsi 106ed (530/106)2 having a focal ratio of 5 gives me a CFZ of 55 microns.

Or  1250/250  = 5F x 2.2 = CFZ 55

That sounds tiny in everyday speak, good thing that I have an awesome high resolution stepper motor focuser.

According to FLI  focuser manual, the total focusing range is a relatively small (but more than adequate) 0.35 inches , the Atlas manages to make an incredible 105,000 precise steps over that range – resulting in each step being only 3.33 millionths of an inch, or 0.085 microns.
 .

	Focus Convergine Calculation
	FLI - Distance Steps	105000
	CFZ mircon	55	0.055 mm
	mm travel	8.89	8890 mircon
	mircons	0.085
	sec trave drawtube	105
	Steps per sec	1000	105 x 1000 steps	105000
	Method:  = CFZ / (Steps  / length of travel distance in Mircon)
	105000 /8890mircon	11.81102	(1 miron=11.81 steps)
	55/11.81 steps	4.66

This leave my CFZ to a 4.66 (5) steps to focus, so the step width in the Focus Convergence setting, Now we need to change the setting in Focusmax focus convergence, start with approximately 1/4th of the CFZ step value:

                                     4.66 x 1/4  =  1.16
                                                                      1 step and 5 samples

Check the focus accuracy if not prefect increase the steps to 1/2th

                                    4.66 x 1/2 = 2.23

                                                                     2 steps and  5 sample

Exposure Time Compensation - Color Filters

Having established the best SNR time using SkyTools and the amount of exposure and time needed to obtain a level of 100 (second best SNR level accordending to SkyTools), you will need to compensate these exposures time depending what filters you will be using: Either RGB or narrowband HOS
.

In the above example the SNR is at100 quality from 20.25 to 21.50, its a 85 min total exposure using lum filter, so its 10 x 8min (or 480 sec), the time total is important, the number of exposure as well as the highest numbers of frames for later stacking the SNR will fall.

Example

Lum  from 20.25 to 21.50 : 85 mins 
Red from 20.25 to 22:00 : 95mins
Green same :95 mins
Blue same :95 mins

The Skytools takes a lots of parameters to establish the best SNR time and number of exposure , but with differeny filters works with different frequencies and therefore we need to establish what proportion / ratios applys.

In order to make "True color" astro images we need to balance the three color channels. This can be done by determining the weight factor for each channel. These weighting factors can be calculated from the response of the CCD chip for each color channel on a pure white light source. Spectral type G2 class V stars are the ideal objects in the sky since they emit pure white light. The measured brightness of such a star through my color filter set tells me how the ICX424 CCD respond to pure white light as passed by each color filter. The CCD response to white starlight, no filters used, will be set as 100%. Due to uneven spectral sensitivity of the CCD (see above) the response through each color filter will be different and only a fraction of the CCD response without any filter, resulting in the following typical color weighting factors for my CCD/Color filter setup.

For deep-sky imaging these weighting factors can be used to determine the exposure times in red, green and blue. Simply multiply the exposure time used for the red channel by the weighting factors for green and blue to get the needed exposure times for the green and blue channel. Such a set of RGB images have "balanced" pixel values so that a white star produces a white image on the computer screen.


For true color imaging the above mentioned factors have to be taken into account.
Example : We want to make a true color image of an object at 30° altitude.
Example : Which RGB weight i needed for this true color image?
CCD response is R : G : B = 1,00 : 0,74 : 0,77
Extinction correction is R : G : B = 1,00 : 1,08 : 1,15 (see graph above)
The total RGB weight for this image will be R : G : B = 1,00 : 0,80 : 0,83
Therefore a set of exposure times could be R : G : B = 60 : 48 : 50 seconds.

R : G : B = 1,00 : 0,74 : 0,77

True color imaging

80/100 x 60 = 48

83/100 x 60 = 50

So, taking the 95 min as base we can work out the following:

80/100 x 95 =  76mins for the green
83/100 x 95 = 78min for the blue
95 mins for the red.