Hubble Space Telescope in Trouble

June 13, 2021, the Hubble Space Telescope shut down after an issue with a 1980s-era payload computer.
Team members continue to work on the issue to get the telescope operational once again.  (Image credit: NASA)

The Hubble Space Telescope, which has been peering into the universe for more than 30 years, has been down for the past few days, NASA said Friday. The problem is a payload computer that stopped working last Sunday, the US space agency said. "There is no definitive timeline yet as to when this will be completed, tested, and brought back to operational status," the Hubble operations team said.

Full story at Phys.Org and Space.com.

Juno Visits Ganymede

Up close and Personal

The Juno spacecraft flew closer to Jupiter’s largest moon than any other in more than two decades, offering dramatic glimpses of the icy orb.

Credit: NASA/JPL-Caltech/SwRI/MSSS

The first two images from NASA Juno’s June 7, 2021, flyby of Jupiter’s giant moon Ganymede have been received on Earth. The photos – one from the Jupiter orbiter’s JunoCam imager and the other from its Stellar Reference Unit star camera – show the surface in remarkable detail, including craters, clearly distinct dark and bright terrain, and long structural features possibly linked to tectonic faults.

Full story/article at JPL.

M90 - Galaxy in Virgo

M90 - Spiral Galaxy in Virgo

M90 - May 13-15, 2021
EdgeHD-11 Telescope - ZWO ASI2600mm Pro Camera
LRGB

Messier 90 (also known as NGC 4569) is an intermediate spiral galaxy with a weak inner ring structure. It lies about 60 million light-years away in the constellation of Virgo. The star formation in Messier 90 appears to be tapering off as evidenced by the galaxy's spiral arms appearing smooth and rather featureless. Galaxies with active star formation have knots and trails of knotted groups in their arms. However, the central region does show some significant activity where there exists around 50,000 stars of spectral types O and B (blue to blue-white hot stars) that formed around 5 to 6 million years ago (young).

This image was created by combining 24 blue, 18 green and 17 red subs, each 120 seconds exposure, to get the master color image (RGB). To the RGB image I added 54, 120 second luminance subs (monochrome) for the detail. I had planned to use 30 of each color, but the Maryland weather this year has been giving me fits!

Remember, complete technical details on all my photos can be found on my Astrobin site.

Creating Starless Images

Astro imaging using narrow band filters (Hydrogen alpha, Ha; Oxygen-iii, O3 and Sulphur-ii, S2) is a popular part of imaging. Not only does it enable amateur astro-photographers like me to take images comparable to the Hubble Space Telescope and other land based observatories but they are a great weapon against the ever increasing light pollution we are all experiencing. They are very effective against light pollution because they only allow a very small range of light to pass (hence, narrowband). The NB images are false color as you assign the three colors of the RGB palette to each NB filter. The Hubble palette (SHO) assigns red to the S2 filter, green to the Ha filter and blue to the O3 filter. Another palette I use is the HOO - a bicolor palette as it assigns red to the Ha and both green and blue to the O3 (no S2 data). 

An obvious down-side to NB imaging is that the stars appear highly tinted in largely purple hues because the full range of color is not processed in NB treatment. So, not only is the nebula rendered in false color so are the stars, which makes them somewhat unappealing.

To correct for this I usually image the main subject using the three NB filters and then run a set of short exposure subs using the standard broadband filters to capture the true color of the stars. Then, in post-processing I create two images, one that has all the stars removed, and another that contains only the RGB stars. Then the two images are combined resulting in a NB nebula but with stars of their proper color and brightness. 

Extracting the stars is a fairly easy process that works well. Removing them to create a starless image is much more difficult. Some of the tools I use to remove the stars leave behind artifacts that must be manually corrected, and sometimes not all the stars get removed - especially bright ones that appear bigger on the image.

Recently, a fellow forum member, Steve, over at The Sky Searchers (TSS) forum posted about a multi-step process to remove stars from an image leaving no unsightly artifacts. Although I haven't fully tested it out on multiple images the results are thus far impressive.

Here are the pre- and post- star removal images of the Rosette nebula.

Unfortunately I don't have a set of RGB stars for this image so I couldn't add them back for the final photo (some folks like star-less images standalone). 

I will certainly add in the RGB session on my next NB project.

Darks vs no darks

One of the features of my new ASI2600mm camera is the low noise levels compared to other cameras. Recall that the 2600's dark frames typically have median ADU values of about 500 (Test of the 2600). And that is consistent over the typical range I use for exposures in my imaging (60-600sec).

Earlier this week I imaged some RGB and Lum subs of M98. Clouds rolled in and ruined the complete set of 60 Luminance subs so all I got was the 20 each of RGB. Not a whole lot of subs to work with, and with short 60sec exposures the amount of data was really low - in fact, only about 20-80 ADU over the noise level of 500.

To make matters worse, my attempts at taking the flat calibration frames produced odd horizontal banding on the images so I couldn't use any flats in my post-processing. Later I found out in my research that the 2600 doesn't like short exposures using a flat panel for illumination. If I had reset the camera gain to 0 (from the 100 I used for imaging) I would have had better results.

So I decided to run a little experiment. I processed each set of 20x60sec RGB subs, one with darks (but no flats) and one without darks (again, no flats). Darks are typically used in processing to calibrate the subs by removing the camera's inherent noise from the images. Since the 2600 has very little noise I wanted to see what I would get if I didn't use dark calibration in the processing.

The results are shown below. The image on the left is the 20x60 sec RGB stack processed normally, but without darks. The one on the right is with dark frames. Neither, of course, had flats, but I cropped the images to remove the vignetting and the dust bunnies weren't obvious in these short exposure images. They look pretty much the same don't they? And indeed, I was just a little surprised at the fact that they did look very similar. The low noise is really a great feature of this camera.

M98 - No darks vs darks
20x60 sec subs EdgeHD11/ASI2600

Now, if we zoom in on the images you can see that the image processed without the darks starts to show some significant noise. The image with the darks is much cleaner. (these images have been lightened to show the background noise better.)

So, I will continue to process with darks and flats. But it was an interesting experiment nonetheless. As for the final image of M98 - although I really want to retake this one with proper exposure times and processing to bring out all the lacking detail and brightness, this image will be used in the M110 contest (award on TSS for imaging all 110 Messier objects). I only have eight more to go!