Comet NEOWISE fading fast

I setup for imaging NEOWISE from my home site on July 26 and the 27th.  Placed my Canon50D piggyback on the GT102 with my Canon 100mm lens. Little did I know that my focus (on both nights) wasn't set properly and so both sets of subs were very sub-par.  After trying to process them multiple times the results were just not worth the effort.  I realized later that the focus ring on my Canon lens is so loose that it can rotate out of focus really easy.  Should have taped it down or used my Tamron which is much stiffer in that respect.

With the moon reaching full phase this weekend, the skies will be awash with moonlight. Once the moon reaches a point where it doesn't rise until after NEOWISE sets the comet will have dimmed to the point where the tail is significantly reduced in size and brightness.  So it's goodbye to comet NEOWISE.  Now I'll be waiting for the next bright comet to favor our skies.

NEOWISE from Mikey's Place

Finally, NEOWISE is high enough that I can capture it from my home with the large telescope mount.  The sky wasn't very good though, lots of thin cirrus clouds.  But I decided to image the comet anyway.

Didn't have time to process the stacked images, but here is a single sub from my Canon50D with 100mm lens piggybacked on my GT102 and AP1100 mount.

Once the subs are processed I'll post the results here.

Comet NEOWISE
July 26, 2020 - Canon 50D/ 100mm f/3.5 60 sec ISO800

Comet NEOWISE - Close Up (Update)

Well, I took another shot at getting a better image.  Processed the 22 x 30sec images taken around 9:45PM.  Since there were more subs the noise was reduced a bit and I got some of the color as well.

Comet NEOWISE - July 18, 2020 9:45 PM
GT102 APO f/5.5  -  Canon 50D  -  22x30 sec ISO800

Comet NEOWISE - Close up

On July 18, 2020, the skies were rather clear and I decided to return to my church's property with my portable telescope setup (William Optics GT-102 APO, iOptron iEQ30 mount, Canon 50D).

I wanted to get some longer exposure images of the comet with a close up on the head and so the GT102 seemed like a good bet.  I realized that I would not be getting a lot of the tail(s). 

After spending about a hour and a half, 212 images later, and lots of processing time at home, I did manage a fairly good close up of NEOWISE.  I am a little disappointed that the image showed very little color.  The green coma was visible, but the final image didn't show it.  The sky conditions were not good enough to capture the ion tail in it's full glory, but I was also disappointed in that I really couldn't pull enough detail out of it as well - also devoid of any color.  Not sure if this is due to processing issues, or sky conditions.  Anyway, here it is.

Comet NEOWISE - July 18, 2020 - ~10:08 PM
GT102 APO f/5.5  - Canon 50D - 10x60sec subs - ISO800

Once the comet gets a little higher in the sky I'll image it once again at home with both my 11" EdgeHD and a piggyback Canon with 100mm lens.  That is if the clouds go away!  Each day that goes by the comet is getting dimmer, and, there are some reports (still unverified) that the nucleus may be starting to disintegrate.  Let's hope not.

Comet NEOWISE at night

On July 15th I arrived at CrossLife Bible Church, Westminster MD, my home church, for our normal prayer group meeting at 6:30 PM.  The service ended at 7:30 and I noticed that the skies were somewhat clearing up toward the north/northwest.  We have a clear view in the direction where NEOWISE would be and so after dropping my wife back home I returned to the church property and setup my camera.

It was 8:40 when I arrived and got setup. There was still a lot of high cirrus clouds covering the sky where NEOWISE is located. I looked for the comet from about 8:50 to about 9:41 and nothing, not with the naked eye, not with 10x50 binoculars. Then, at 9:45, I spotted it! Shinning through the thin clouds it was still a splendid sight.

Comet NEOWISE, July 15, 2020 10:06 PM
18mm, f/5.6, ISO 1600 15x5 sec

It was about 74 degrees, with a strong wind (it's always windy at the church since we sit at the top of a hill and for some reason all the air rushes right over our site). I knew I would lose some shots just due to the camera being buffeted by wind gusts over 20mph. But my patience paid off.

I took 118 images, and processed four different sets. One of those sets produced a fairly good image of NEOWISE even considering the image was shot through a layer of clouds.

Comet NEOWISE, July 15, 2020 10:08PM
270mm, f/6.3, ISO1600 10x5sec

This image of NEOWISE was taken at 10:08 PM with a Canon 70D and Tamron 18-270mm lens. The lens was set at the full 270mm focal length and aperture at f/6.3. I took 21 subs, of which I used 10 in the final stack. Each was taken with an ISO of 1600, exposure time of 5 seconds. The subs were pre-processed and stacked with Nebulosity 4.0, and the stacked image further processed in PixInsight and Paint Shop Pro. I did take darks to limit the sensor noise and hot pixels, but Nebulosity didn't do such a good job removing the pixels. You can see them in a zoomed-in version of the photo as streaks of colored dots.

Now that the weather is not looking so good for the next week or so, it looks like the next photo opportunity will be at my home with the WO-GT102 telescope on my AP1100GTO mount. The comet will likely fade a bit by then (it is moving quickly away from the sun) but it will be much higher in a darker sky, and finally high enough to clear my tree line.

First Images of Comet NEOWISE

Early this morning I was able to capture some initial images of C/2020 F3 NEOWISE.  I had provided some charts in my previous post and with NEOWISE only getting about 10 degrees up in the NE there was no chance I could image it from my home. So I packed up my Canon 70D and headed to my church property in Westminster. I decided against bringing my portable telescope figuring I try with just the Canon on a tripod and see what I could get.

The first photo is a composite (stacked) image of 10, 2sec exposures, at a high ISO value of 3200. The Tamron 18x270 lens was set to 77mm (I had wanted 100x but somehow the zoom slipped) at f/5.6.

C/2020 F3 NEOWISE, July 9 2020, 4:54 AM
Canon 70D, 77mm, f/5.6, ISO 3200, 10x2 sec

The second is a composite of 10, 1 sec exposures at ISO 1600, 270mm, f/6.3.  Since these exposures were taken rather late, the sky had brightened considerably. Lens fogging didn't help either!

C/2020 F3 NEOWISE, July 9, 2020, 5:06 AM
Canon 70D, 270mm, f/6.3, ISO 1600, 10x1 sec

Neither set of images were processed to eliminate/minimize noise, so they are a bit noisy.

Plan is to take a few more later this week, potentially Saturday morning, weather permitting.  Then, when NEOWISE makes it to the evening skies, I'll image with the either the GT102 or the EdgeHD11.

Comet C/2020 F3 (NEOWISE)

Well, surprise, surprise ... one of the newly discovered comets might actually be visible and is not breaking up.  With the demise of ATLAS and SWAN I was hesitant to report on any hope of sighting a comet with the naked eye anytime this year.

But, NEOWISE is still going strong and is now positioned for the northern hemisphere.

If you want to see NEOWISE you have two choices.  Early in the morning, before sunrise or (later in the month) just after sunset.  It is probably the brightest right now and will be dimming slowly over the next two weeks so catching it in the AM might be worth the early rise from bed.  For those who prefer their sleep, it will be visible in the NW after sundown, and will be rising higher and higher in the sky (important if you are viewing from a location with lots of trees - like at my observatory.)

The two charts below will give you a rough idea of where to look for the comet.  Each one is fixed at a particular time (roughly with the sun about 10 degrees below the horizon) and shows the position of the comet on each day from July 6th through the 25th.

Comet NEOWISE - Morning
Reisterstown, Maryland

NEOWISE doesn't rise very high in the early morning sky as it moves around the sun in it's orbit. It is the highest on July 10th, about 15 degrees above the horizon at 5:00 AM.  Distance between each horizontal grid line is 20 degrees.

The evening views are a little better, and the comet gets higher each succeeding night, but also dims as well.

Comet NEOWISE - Evening
Reisterstown, Maryland

Recent reports put comet NEOWISE at magnitude 1 - 2, which is certainly bright enough to be visible with the naked eye, but I would bring along a pair of binoculars if you have them.

Depending on the weather, I may be transporting my portable telescope to try to capture some images.  Later in the month, when the comet is high enough to clear my treeline, I'll capture it with my larger rig.

Graphics courtesy of Starry Night®
(Starry Night Pro) (Version 8) / Simulation
Curriculum Corp.

A Globular, a Star Cluster and Three Galaxies

The new mount is performing admirably. Still a few items to take care of and calibrate, but the full functionality is working just fine.

First up is M68. Messier 68 is a globular cluster in the equatorial constellation Hydra. It was discovered by Charles Messier in 1780. William Herschel described it as "a beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together". His son John noted that it was "all clearly resolved into stars of 12th magnitude, very loose and ragged at the borders". (Wikipedia)

M68 Globular Cluster in Hydra
EdgeHD-11 / ASI1600mm camera
40x10sec Lum

This monochrome image was taken on May 31, 2020, with my EdgeHD-11 and ASI1600mm camera. A combination of 40 luminance subs using very short exposures (10 sec).

Next is M88, a spiral galaxy in the constellation Coma Berenices. Recent analysis puts it at about 61.94 million light-years distant. It was discovered by Charles Messier in 1781. M88 lies in the thick of what is called the "Realm of Galaxies", and is among the brightest of the spiral galaxies in the Virgo cluster. The full extent of the disk, about 125,000 light-years across is dominated by dust all the way to the core of the galaxy.

M88 Spiral Galaxy
EdgeHD-11 / ASI1600mm camera
100x60sec Lum; 50x60sec RGB

This photo of M88 was imaged between June 8 and June 10, 2020. At 2.5 hours total integration time, it is composed of 100x60sec L subs and 50 each of 60sec RGB subs.

Next up are two elliptical galaxies, M49 and M89. Elliptical galaxies are a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. (Wikipedia)

M49  is located about 56 million light-years away in the equatorial constellation of Virgo. This galaxy was discovered by French astronomer Charles Messier on February 16, 1777 and was the first member of the Virgo Cluster of galaxies to be discovered.

M49 Elliptical Galaxy
EdgeHD-11 / ASI1600mm camera
100x10sec Lum

M89 is another elliptical galaxy discovered by Charles Messier on March 18, 1781. It is also located in the constellation of Virgo, about 50 MLY from earth. It is nearly perfectly spherical.

M89 Elliptical Galaxy
EdgeHD-11 / ASI1600mm camera
100x10sec Lum

Finally, an open star cluster, M18. This cluster of stars, in the constellation Sagittarius, was discovered by Charles Messier in 1764. It is relatively close lying at about 423,000 light-years distant. It is a sparse cluster about 26 light-years across. This image was taken on June 13, 2020.

M18 Open Star Cluster
EdgeHD-11 / ASI1600mm camera
20x10sec RGB

Busy "Day" with the EdgeHD

Yes, the emphasis is on the word 'day'.

One of the unique capabilities of the Astro-Physics mount is that it can allow you to start your imaging session in the east with the counterweights UP.  Now that probably doesn't mean a whole lot to those of you who are not astro-nuts like me (and there are others of course who do get it). But one of the scary times of a long evening's imaging session is when the scope passes the meridian.

The meridian is an imaginary line that extends across the sky from due south to due north. It is the point where a German equatorial mount has to stop tracking, flip completely around to the other side of the pier, re-acquire the object it was tracking and then continue. Now I have had a relatively good success with my meridian flips. But even when they work you lose some precious imaging time while the scope re-acquires the object, and because the camera is now also flipped the post-processing gets a little trickier. When they don't work, the telescope stops tracking and you are done for the evening (if you are in bed).

But the Astro-Physics mounts allow you to start in the east with counterweights up, thus not requiring any flip. But there is a problem with this scenario - with the telescope essentially upside down the camera can find itself dangerously close to hitting the pier (or equipment that might be mounted on the pier). It has the issue when you are trying to image at high declination values (for you non-astro-nuts), that means directly overhead or to the north. So, we need to make sure that doesn't happen.

Astro-Physics APCC Users Guide

And that is what I did today. During the cool of the evening, while it was still light outside, I mapped out the whole allowable movement space of the mount for each declination 5 degrees at a time. With that data the mount has a mapping of the sky where the telescope is free to move without fear of striking the pier. A safe-zone so to speak. Took a bit of time, but well worth the effort.

Now, if only the skies would clear so I can try out this new capability.

Supernova in M61

Earlier this month I spent some time installing my Off Axis Guider (OAG) on the Edge11.  With new spacers I was able to get the OAG to work pretty good.  I was still having issues with the FOV and sensitivity of my guide camera though and so finding a star and guiding was still problematic.  I since purchased a new guide camera based on reviews and comments of the folks on the forums I frequent - the ZWO ASI174mm. This camera has solved my OAG problems of getting decent stars to guide on.  Alas, the clouds rolled in and I have not been able to image anything with the new OAG setup.

But, back on May 13 when setting the spacers I was able to capture M61, a spiral galaxy in the constellation of Virgo. I was using this field of view as my test view for getting the focus on the OAG worked out.  Although I did process the image later that night, the focus was still a bit off due to terrible atmosphere conditions, but I still wanted to get the RGB stack processed to show the supernova (SN 2020 jfo) that appeared in the galaxy.

Here is the image showing the galaxy (cropped up close) with the supernova marked. The power output of an exploding star is immense. This star (or what's left of it) is almost brighter than the entire core of the galaxy!  The other three bright stars are foreground stars in our galaxy between earth and M61.

M61 with SN 2020 jfo
Edge11 and ASI1600mm RGB 20x60sec each

The Magic of Image Processing

The Magic of Image Processing - Part I

Over the years I have been asked by friends to explain how I get my beautiful astro-photos, especially from a light polluted sky near Baltimore.  Well, the actual process is pretty complicated and sometimes intense, both in the time and effort put into it as well as the techniques used.  But I'll try to outline the basic steps.

Please note that it is not my intention to provide a detailed account on how this is all done by providing the complete steps, but just to give an overview and high-level look at the workflow.  Part I of this post will cover the capturing of the data and the initial calibration and stacking to get a single master frame.

For this example I am using a section of the Leo Triplet image that I posted on Astrobin back in March of this year (see image above). In particular, M65, an intermediate spiral galaxy about 35 million light-years away in the constellation Leo. In the image it is the galaxy in the lower left.

First step, of course, is to actually photograph the object.  Although this is not part of the post-processing effort, without it there would be nothing to process!  The original photo is a combination of RGB and L subs (subs are the individual photos - many are stacked in the post-processing to create the final image). For the purpose of this discussion I will be using only the luminance subs (monochrome; no color) to make matters a bit simpler. I will be using 64 of the original 70 L subs, each one taken with an exposure of 120 seconds.  Images were taken through my 4", GT102 APO refractor with a ZWO ASI1600mm cooled monochrome camera.

Once we have a good set of raw photos (no star trailing, out of focus, airplane trails across the image - yes, happens a lot) they go through three steps: calibration, registration and integration.

Calibration

Images (subs) of our object are known as lights. Since these raw subs contain additional data that we do not want they must be calibrated to remove, or largely minimize, the bad signal from the good signal. What are the bad signals? Thermal noise from the camera itself, uneven light across the field of view and electronic read noise are the three basic ones.

The thermal noise is due to the fact that heat from the camera itself builds up and triggers the sensor just as light does. With exposures sometimes exceeding 5-10 minutes per sub this buildup can be rather large. And since the amount of signal is proportional to the temperature of the sensor, the higher the temperature, the more heat signal the sensor collects. This is mitigated to a large extent by cooling the sensor and most astrophotography cameras are equipped with thermoelectric coolers. My camera is typically cooled to -20 degrees Celsius (-4 degrees F) even in the summer.

Uneven light is the vignetting of the image due to the optics of the telescope/camera combination. The intensity of the light fades off as it approaches the edge of the sensor. In addition, dust particles on the sensor glass (and filters) produce faint halos and spots (dust bunnies) on the image.

Then there is the noise produced by the very process of reading the data from the sensor.

Calibration is the process of removing as much of this unwanted data as possible.

To remove the thermal noise, special subs, called darks, are taken which are used to remove the thermal noise from the original lights. These dark frames are subs with the same exposure times as the lights but with the sensor closed off to any light. The signal contained in these dark frames is therefore only from the thermal noise. If we subtract the darks from the lights we get a resultant sub that has the thermal noise removed. This process relies on the randomness of thermal energy and is too complicated to fully discuss here, but you get the idea.

The unevenness of the light frame is corrected by the use of a flat. Flats are subs taken through the telescope in the same configuration as when it was taking the original lights. A uniform light source (the daytime sky through a tee-shirt, or an electroluminescent panel) is used to make sure the sensor receives just the view of the optical train with no subject matter - nice uniform, even light. These flat frames, which contain only the dust shadows and the fall-off along the edges, are then used to correct for the vignetting and shadows by dividing the data on the light by the flat data. Again, a bit complicated.

Finally, bias frames are taken to subtract the read noise from the image. These are taken with no light and exposures of as close to 0 seconds as possible as we only want the information produced from the camera's electronics in reading the data off the sensor. These bias frames are then subtracted from the lights as well. In the case of my particular camera, I don't use bias frames, but use dark flat frames instead. Again, too much to discuss for now.

The following diagram may help to visualize what is taking place.

Deep Sky Stacker

I typically create about 40 dark frames to create a single master dark; about 20 dark flats, and 20-25 flats. Multiple frames are taken to reduce the random noise within these calibration frames and produce a more even image.

With my darks, dark flats and flats ready to go I can now calibrate the 64 lights of M65 using a program called PixInsight, my software of choice. This same program will also be used post-calibration to complete the images.

Registration

Registration is the process of aligning each of the calibrated lights to a reference frame so that they all line-up together. Although the telescope is tracking the object closely during the exposure, it is not perfect. And it is actually desirable not to have every frame line up perfectly. I intentionally move each image a small amount when taking the exposures in order to further randomize the noise and other unwanted signal data. This process is known as 'dithering'. 

Integration

With all the light frames now fully calibrated and registered its time to combine them all into one master frame. This is the process of 'stacking'. You might have been wondering why we don't just take a single long exposure shot of the object. There are lots of reasons. Remember in the discussion above how the sensor temperature plays into all this? A single 60 minute exposure would produce a lot of thermal signal (probably too much to eliminate). And then there is the guiding. Even a high-end quality mount might not be able to track precisely enough over an extended amount of time (although with accurate polar alignment in a permanent observatory it probably could). Finally there are the other annoyances - i.e., 18 minutes into a 20 minute sub an airplane passes right through the field of view, producing those 'lovely' bright light trails over the image! For these reasons, and one more 'big' reason (to be discussed really soon), we typically take lots of smaller exposure subs and then combine them to get the final image. In other words, take 60, one minute subs instead of one, sixty minute sub.

So, what's that other big reason?

Thankfully, because of the nature of the universe, the way God created it, noise is random. Every time you take an image the information on the camera sensor that was due to thermal and other forms of noise is a little bit different than in the previous image. Over time it averages out to a certain quantifiable level, but every pixel on a frame, and every frame, will have differing levels of brightness - the actual signal from the object (what we want) and some random amount of signal from the noise (what we don't want). Since the object's signal is constant, and not random, the contribution of total energy from the object builds up as you might expect - one unit of signal multiplied by ten frames equals 10 units of signal. But since the noise is random, multiple frames produce a final total noise energy that does not add up uniformly. The contribution due to noise will be slightly less. How much less? Proportional to the square root of the number of frames less. This means that if I double the number of subs, the real signal increases by 2 but the noise increases by 1.414 (the square root of 2). One way to measure this is by calculating the SNR, or signal to noise ratio.

Astrophotographers pay particular attention to the SNR. This is simply the amount of signal divided by the amount of noise. The higher the SNR, the better. So, for example, lets say a sensor pixel picks up 100 photons of light every second. In one second the SNR would be:

But if we expose for 100 seconds (or the average of ten 10-second exposures) we would get a SNR of:

The higher the SNR, the better the final image will be. Therefore, more subs are better than a few subs. In fact, it is not uncommon for astrophotographers to take 60-200 subs (of each filter) to get the final photo.

OK, enough words and theory, lets see what this all really means.

Here is a single light frame of M65 (120 seconds at f/5.6):

Hmmm, not much showing up!  Where's the galaxy?

Well, it's there, just hard to see. Why?  Because most of the signal is buried deep in the low end of the image spectrum. This object is rather dim, and so there isn't much signal to capture in 120 seconds.

We are going to detour a bit from our processing discussion to discuss how digital cameras work as this is necessary to understand some of the processing techniques.

For simplicity let's imagine that the pixels on a camera sensor are little buckets. Each bucket can only hold so many electrons. As a photon of light strikes the sensor, an electron is created and is stored in the bucket. My camera, for example, has a sensor that can have data values from 0 to 4095. This is called the dynamic range of the sensor. My buckets can hold up to 4096 electrons.

Now, the higher the data value in a bucket, the brighter the pixel in the resulting photo. Buckets that are empty will produce a totally black pixels in the resultant photo. Buckets that are partially filled will produce varying shades of grey.  And, if a bucket fills up completely, you get pure white.

If I was to take a photo of the moon, or some other bright object, the pixels on my camera will fill up pretty fast. And, there would be some that have no data (dark areas) and some that have lots of data (light areas) and some that are in-between.  In a completely white, overexposed frame, every bucket would be full (4095 electrons). But in the case of dim objects like galaxies, nebulae, dust clouds, etc., even after exposing the sensor for minutes at a time most of the buckets only fill up a little bit.

So, in the single sub above, the vast majority of buckets have near zero data values (dark space) and only a few have maybe 10-500 electrons in them. So the range of the data in the image is only 0-500 out of the possible 4095. My buckets are only about 1/8th full at best. That's why the end result is pretty unimpressive. The few pixels that have information in them only produce very dark shades of grey, with a few producing some brighter whites.

But what if we multiply each pixel/bucket value by some factor so that each bucket appears nearly full.  In the case of the image above, since the largest bucket amount is only 500, if we multiplied each by 8 we would end up with buckets that are filled, or nearly filled, and therefore would create a photo where most of the pixels (that at least contained some electrons) would now have much larger values and therefore appear brighter.  We essentially do just that, by a process known as stretching. It isn't as simple as multiplying every pixel with a single value, as the stretch is usually non-linear, but for simplicity the analogy works.

Here is the result of stretching the single light sub.

And there's the galaxy!

But, there's all the noise too.  Since we amplified all the sensor data, the noise was amplified as well.

Now, back to the main discussion.  Here's where the stacking comes in. Remember how we discussed the fact that noise grows slower than true signal?  We use that concept to get an image that contains a lot of data, but over many light subs instead of a single long sub. Thus, we can 'eek out' good data and limit the bad - the SNR gets larger.

The following set of images show progressively larger stack sizes starting with 4-stack and ending with 64-stack; each one twice as large as the previous. You can see how the actual galaxy gets brighter, more detail starts to show and the noise goes down. Note that these have been stretched so you can see the images, but the actual stretching process occurs later in the post-processing steps.

We now have a good master image made up of 64, 2 minute images. The resultant master is basically equivalent to a single sub of 128 minutes, but without the huge amount of noise that a single image like that would have.

In Part-II I will show how we take the master light out of the calibration and integration step and using PixInsight's post-processing routines reduce the remaining noise, enhance the image's detail and adjust the overall quality of the final image. I'll also discuss how color is added to the final image.