Sunday, June 05, 2016

Mars and Saturn near opposition

Mars was at opposition (directly opposite the Sun from the Earth) on May 22, and Saturn was at opposition on June 2.  I've been itching to get some photos of them, and the combination of clear skies, reasonably good seeing (low upper-atmosphere turbulence) and time available made last night a good choice.  Without further ado, the photos:

Although the photos say "June 5" I took them the night of June 4, local time, at about 10:12 PM and about 11:22 PM Mountain Daylight Time, from our back yard in Fort Collins, Colorado.

My equipment was a Meade LX90 ACF 8" f/10 Schmidt-Cassegrain telescope mounted on an iOptron CEM-60.  The camera was a ZWO ASI174MM monochrome camera, with an RGB filter wheel and a 2.4x Barlow, which made the combo a 4800mm focal length f/24 system.

Mars was taken with a 1.9ms shutter and a gain of 280 in FireCapture.  It was a 640x480 ROI, running at 182 FPS.  Saturn was taken with a 6.89ms shutter and a gain of 351, also a 640x480 ROI, but a lower FPS at 121.

Both images are stacks of the best 500 out of 1000 of each of red, green, and blue, stacked with Autostakkert 2.6.6, with a drizzle of 1.5x (which made the net size of the image 960x720).  Before stacking, I normalized the brightness in Photoshop.  On Mars, I brightened red by 3x, green by 2x, and blue by 4x.  On Saturn, I brightened red by 6x, green by 4x, and blue by 8x.  This was to make it easier for Autostakkert to align (and easier for me to pick alignment points!).  On Mars, I aligned on the planet center.  On Saturn, I aligned on the planet center as well on the extrema of Cassini's division at the upper right and lower left.

After stacking, I brought the resulting R, G, and B images back into Photoshop.  I sharpened them up with its Smart Sharpen filter with a 7.5 pixel diameter, assigned the proper channels, then tweaked the final brightness and saturation for a pleasing image.

Just for fun, here is a raw green image of Saturn, along with a stacked green image of Saturn, to demonstrate how much processing goes into these results. First, the raw green image (one of 1000 such images):

Next, the stacked green image:

Finally, the same for Mars.  A raw green image:

And the stacked green image:

Some day I should try this from someplace not directly down-wind of the turbulence-inducing Rocky Mountains.

Tuesday, May 10, 2016

Transit of Mercury, May 9, 2016

Today (well, technically, yesterday now) was the 2016 Transit of Mercury.  These happen much more frequently than transits of Venus.  Mercury transits happen about every 7 years (13 or 14 times per century).  I was watching  the weather anxiously - I wanted this to be a dry run for the 2017 eclipse, but I was not able to travel on Monday so I was hoping that the weather would suffice here in Fort Collins.  I watched the Fort Collins cleardarksky page continuously over the weekend, which helped me stay calm and collect my equipment to prepare for the expedition.

Monday morning started with low clouds which cleared by about 6:30 or so - just in time for me to have all my equipment set up:

From left-to-right, these are:

  • A Meade 2045 4-inch Schmidt-Cassegrain telescope on a tripod, with a glass front-surface solar filter.  This was for visual use - which turned out handy, since I had about 8 or 10 visitors.
  • A Lunt Solar LS60PT pressure-tuned H-alpha dedicated solar scope, with a Hinode Solar Autoguider and a ZwO ASI174MM camera. These are all mounted on an iOptron CEM-60 equatorial mount. The telescope is a 60mm f/8.3, or about 500mm focal length.
  • An Orion ED80TCF apo triplet, with a Baader Herschel wedge and a Canon 7DmkII attached (with a roughly 1.5x Barlow in-line to extend focal reach).  The telescope is an 80mm f/6, or about 480mm focal length.
The white posterboard next to the telescopes is covering up my computer, which was controlling both the ZwO and Canon cameras.  Sadly, the software I was using for the ZwO had a glitch - every so often it would decide to stop its sequence and not tell me.  So I would not notice for 20 or so minutes, missing many photos :-(

A little more about the Hinode autoguider.  This is a very handy device.  It plugs into the autoguider port on the mount.  It was about as close to fire-and-forget as you can get for solar observation.  I was not able to get the mount well-aligned before sunrise (too many clouds, slept in too long), so this was a life-saver.  Here is a closeup of the autoguider:

While babysitting the computer, I managed to get an iPhone shot through the eyepiece of the Meade - just to compare with what I actually got with dedicated cameras. Mercury is the smaller dot on the right:

As the morning progressed, the clouds started rolling in, much to my frustration:

That said, it was a much better day than I had been expecting the previous week.  After 7+ hours out, Mercury finally slid off the face of the Sun, and I had some equipment to pack.  Here are the scopes at the end of the session - see how far they rotated to counter the Earth's motion:

And now, the moment you all have been waiting for.  Here is a composite picture of several moments during the transit, taken in H-Alpha light:

The two steps in the middle are closer together because of that computer glitch I mentioned earlier.  Here is an animated GIF:


And here are two videos on YouTube.  First, white light:
Next, H-Alpha:

And now, for bed.  Nearly 24 hours after I woke up to start the excursion.  2017 is coming fast!

Edit (morning of May 10):

I also made a composite and animated GIF of the white light images.  Note how the path of Mercury curves - this is because this telescope was mounted on an alt-azimuth mount.  It follows the sky, but it is not aligned with Earth's polar axis:


Here is what it looks like with everything rotated to correct for the "field rotation" caused by an alt-azimuth mount (especially when you track from the horizon to the zenith):

One thing to note: both the white light and H-Alpha sequences are mirror-reversed, since both telescopes have a diagonal mirror / prism in the light path.  I did not bother to correct for this, since this is nothing you could see with your naked eye :-)

Saturday, February 06, 2016

Moon, Venus, and Mercury - Feb 6, 2016

I got up really early again this morning to catch the Moon, Venus, and Mercury dancing in the pre-dawn sky.  Here are a couple of my best shots.  The first one was taken from Larimer County Road 38E, where it curves into the foothills.  It was taken at 5:55 AM with a Canon 7DmkII and an EF 100-400 f/4.5-5.6L II lens, at 100mm f/4.5.  It is a 1.6 second exposure at ISO 800:

For the curious, here is a map of the foreground showing what is visible in the 12.8 degree field-of-view of the lens:

I drove home, and snapped one more picture above the neighbors' rooftops.  Same camera/lens/exposure settings:

OK, *now* I can stop waking up early in the morning.

Thursday, February 04, 2016

Five Planets and the Moon

I got up this morning very early to make an animation of Jupiter, Mars, Saturn, the Moon, Venus, and Mercury as they rose in the early morning sky.  Here is the finished product:

It was very cold - 7 degrees Fahrenheight - and very early.  This is a 30-minute sequence starting at 5:39 AM and finishing at 6:09 AM.  All of the images have the same parameters:
  • Canon 7DmkII camera
  • Canon 8-15mm f/4L lens, locked at 10mm (widest useful zoom with this lens on a 1.6x crop camera)
  • 8 second exposures at ISO 3200
  • Image sequencing performed by Canon's EOS Utility.  A capture was started every 15 seconds.

That camera/lens combo yields a 180-degree diagonal field-of-view.  Jupiter and Mercury are about 120 degrees apart in these images, so this gives some extra room for animation and cropping.

Capturing all five planets in the pre-dawn skyglow is surprisingly tricky, especially when city light pollution is contributing to a murky lower atmosphere.  I was located at the north end of the parking lot for the Foothills Trail, above Horsetooth Reservoir on County Road 23.  Here is the best of the single frames I captured.  It is not bad - but the skyglow completely obscures Mercury, and even mostly hides Venus - even though the image was being processed as a 16-bit-per-component TIFF:

To fix this, I created a correction layer in Photoshop.  I first began by blurring the entire image with a Gaussian blur of about 25 pixels.  I then selected the region near the treeline / horizon, and did a "Maximum" filter.  This shrank the size of the trees down so they did not interfere with the mask I was making.  I then selected the whole sky, and copied it to a new layer.  This new layer was then hit with a "Minimum" filter over the entire sky.  This removed the stars and most of the planets.  I had to use the "Healing Brush" tools to finish removing the Moon and Jupiter.  A little touch-up on the skyline, and I had this mask:

I then recorded an Action which selected this mask, pasted it into each image, changed its blend mode to "Subtract", decreased its opacity to 50%, merged the layers, and then cropped and resized the image to 1920x1080 (HD resolution).  I replayed the Action with Photoshop's automation tools, then assembled the whole animation in Premiere Pro.

Here is that same shot as the first one, cleaned up pretty much as described (with some extra care taken with the skyline, and some additional contrast boost to bring out the planets):

And here are the labels to show the named stars and planets visible in the picture (not counting the Earth, of course!):

Fun trivia: You can see the trails of 5 early morning runners at about 0:10 and 0:27 in the video.  The last shot was an accidental selfie - it is hard to tell where the edge of the frame is when you are shooting with a 180-degree field-of-view!  I count six cars that passed on County Road 23.

Edit (Feb 5, 2016): Here is a different way to visualize the sequence of image I took - star trails.  Without labels:

And with labels:

Edit 2 (Feb 6, 2016): I refined my processing formula.  I gave GradientXterminator a try, ,but was not very happy with it.  So I spent the time to make a very detailed foreground selection mask, and then changed the formula to:

  • Duplicate the image into a new layer
  • Load the foreground selection mask
  • Select the new (topmost) layer
  • Do a Maximum filter of 25 pixels width ("preserve roundness")
  • Remove the selection
  • Do a Gaussian Blur of 20 pixels width
  • Do a Minimum filter of 25 pixels width ("preserve roundness")
  • Adjust Levels to a gamma of 0.75 and a maximum of 192
Here is the updated video:

And, inspired by my brother-in-law Edward Plumer, I made a version of my best image with constellation lines and labels.  Here is the reprocessed best image:

And here it is with the labels:

Edit 3 (Feb 7, 2016): Check out my brother-in-law Edward Plumer's blog - we have a friendly competition going for this kind of thing.

Copyright note: this page, the video, and the images linked are Copyright 2016 by Ross Cunniff under Creative Commons.  Any use is fair use as long as attribution is made.  The music to the video is "Starway" by Jaja - - also licensed under Creative Commons.

Monday, September 28, 2015

Total Lunar Eclipse, September 27-28 2015

Jill and I went eclipse chasing this evening.  I did initial research on the Clear Dark Sky site to see what conditions were going to be like.  After digging, I decided that somewhere south and east of Briggsdale was likely to have clear skies.  We ended up on the grounds of an old church called Osgood Church.  We were greeted by this raptor, which we took as an auspicious omen:

We were rewarded with gorgeous skies - only a few wispy clouds floated through occasionally.  Here is an all-sky shot taken with my Canon EF 8-15mm f/4.0L lens on a Canon 5DmkII camera that shows how nice the skies were:

Jill and I are there in the foreground next to the telescopes.  You can see the eclipsed Moon, as well as the Milky Way and the skyglow from Fort Morgan, Sterling, and smaller towns off past the horizon.

For the eclipse photos, I used a Canon 7DmkII camera on an Orion ED80T CF refractor - an 80mm diameter, f/6.0 480mm focal length triplet.  I mounted it all on my handy portable iOptron MiniTower Pro.  We were nearly faced with disaster when my inverter failed to power on - fortunately, our Jeep had plenty of 12V power to drive the mount.

I took shots every two minutes - and will eventually make an animation - but here is one of the better shots at mid-eclipse:

This was a 4 second exposure at ISO 3200.  In between my every-two-minute exposures, I wandered around and took pictures of our surroundings.  Here is another selfie of Jill and me with the eclipse - 30 second exposure, ISO 3200, Canon EF100-400mm f/5.6L lens on the 5DmkII - the long exposure streaked the moon and stars):


Here is a context view of our trusty steed, my telescope setup, and Jill taking pictures with her camera, with the church in the background.  Taken by moonlight, hand-held (I love image stabilization...)

I got one shot of the ending partial phase near the chimney of the church - I used a flash to fill in the foreground and tightened down the aperture to f/18 to increase the depth of field:

Staying up for another couple of hours, I made this collage and then went to bed.  Some time later this week I'll try for an animation.

Edit: I must have been sleep-deprived last night.  I re-used a template I had made for the 2010 Lunar Eclipse and forgot that it had a left-right reversal built in due to the fact that those photos had been taken with a mirror diagonal.  Here is the corrected collage:

Edit: here is the YouTube time-lapse video I made:

Wednesday, August 05, 2015

Armchair science

I noted with interest this update from the DSCOVR mission:

Cool!  The DSCOVR mission is an Earth-imaging mission that takes a continuous stream of Earth images to monitor it for climate and other changes over time.  It happened to catch the Moon crossing the face of the Earth (go to the link for the animation - you'll be glad you did).  This will happen twice a year, when the plane of DSCOVR's orbit intersects the plane of the Moon's orbit in line with the Earth.

The DSCOVR web page says that the satellite orbits "a million miles" from Earth.  It turns out, you can calculate that distance just from this image and from the known sizes of the Earth and the Moon.  The Earth has a mean radius of 3,959 miles, and the Moon has a mean radius of 1,079 miles.  The ratio between the two is 3.67 - meaning the Earth is 3.67 times as big as the Moon.  But if you open up that image in Photoshop and measure the Earth and Moon in pixels, you will find this:

The Earth is 1595 pixels big, and the Moon is 596 pixels big.  This is a ratio of 2.72 - what's up with that?  The answer is, perspective.  The Earth is farther away in this picture than the Moon, so it looks smaller.  We know that the Earth and the Moon are roughly 250,000 miles apart.  So, how far is DSCOVR from the Earth?  Based on these measurements, this diagram, and a little trigonometry, we can calculate it:

Point "S" is the spacecraft.  Point "E" is the north pole of the Earth.  Point "M" is the north pole of the Moon.  Point "X" is the center of the Moon, and point "Y" is the center of the Earth.  We know the following distances:

  • Point X to point M: 1,079 miles (and 596 pixels)
  • Point Y to point E: 3,959 miles, (and 1,595 pixels)
  • Point X to point Y: 250,000 miles

The dashed line shows the projection of the edge of the moon from the spacecraft's point-of-view. The pixel measurements are taken at the same distance - since they are both projected against the same plane (in reality, the plane of the imaging system).  The point labeled "Mp" is that projected point in the image.  We have similar triangles which can help us figure out the distance D:

  • Triangle Y-S-Mp
  • Triangle D-S-M

The image shows the calcuations, which gets a distance of 965,000 miles.  Close enough to "one million miles" for government work!  Especially given the precision with which I specified the Earth-Moon distance (the actual distance varies between 221,457 miles and 252,712 miles).

Finally, here is a picture showing how big the Earth would have looked if it had been at the same distance as the Moon in the DSCOVR photo (I show it as a dim ghost behind the original image):

Of course, we would all be having a very bad day if the Earth and Moon had been at the same distance at that time...

Edit (Aug 5 7:15PM MDT): I had an email exchange with Phil Plait, the Bad Astronomer, and he pointed out I can get the exact Earth-Moon distance on the day in question (July 16) from the United States Naval Observatory website.  On that date, it was 243,388 miles.  So, plugging that into the formula I get that DSCOVR was 940,000 miles from Earth on that date.  L1 is about 929,000 miles from the Earth-Moon barycenter, which in this photo is about 2900 miles closer to the spacecraft than Earth is, making the L1 point 932,000 miles from the center of the Earth.  Which is very close to what I calculated - less than 1% difference.  Part of this is difference is attributable to the inaccuracy of measuring the pixel sizes of the Earth and Moon, and part is attributable to the fact that DSCOVR is not actually *at* the L1 point; rather, it is orbiting about it in a complex pattern known as a "Lissajous Orbit".

Given that complex orbit, this method is probably the most accurate way I have of conveniently determining DSCOVR's distance from the Earth.  At least on the days that the Moon occults or is occulted by the Earth.

Phil also pointed out that the moon will look smaller due to perspective when it is on the other side of its orbit (the back of my envelope tells me it will be 59% of the apparent size) - so it might look something like this by comparison:

And  yes, I'm showing the other face of the moon - that's the one DSCOVR will see in that geometry.  We'll see...

Saturday, August 01, 2015

*Big* Pluto Icosahedron

I made a Pluto icosahedron from my previous post, and I decided it was nice - but it needed to be bigger.  So I spent today figuring out the geometry to maximize size while minimizing paper.  Here's what I came up with - an icosahedron twice the size as the previous one, taking 4 sheets of paper.  It will be a little more complicated to assemble - you have to match all of the tabs just so - but it makes a nice model when it is complete.

It is in PDF format, since it is four pages.  Without further ado - Pluto.