An unexpectedly good Jupiter

I made these images from a couple of videos that seemed rather average; I even told people the conditions had not been good this night, and the whole trip was not worth the effort. That was before I started processing the videos. I was pleasantly surprised by the amount of detail that popped out during sharpening. The DIMM seeing at the time was also unimpressive, only 1.3 arcsec, but I guess there were enough good frames interspersed among the blurry ones to get a good result. Captured from Ederi, Dec 03 2011. 

A short video is avilable at http://www.youtube.com/watch?v=r8HY_1zHq_w

Two Jupiters and a double star

A couple of Jupiters captured some time ago. First, a big Jupiter from back in September on a night of good seeing. I spent the night at Agios Pnevmatos above Rethymnon, and the views were magnificent. My mirrors were however rather dirty, and although one always hears that it is not possible to see any difference between a very dirty and a clean mirror, the camera certainly noticed a difference. For this picture I tried the de-rotate function in WinJupos. It improved the details on the disk  but caused a ring to be visible not far from the edge of the planet.

My second picture is from Oct 22, just after I cleaned the mirrors. I could use less gain in the camera after cleaning, and the contrast was better. The transiting moon is Io. Captured from my terrace.

Lastly, in a departure from the usual planet images, I present an image of one of the pairs in the "double-double". Is the collimation a bit off perhaps? That's all :-)

Jupiter from Chania

Lately I have been exploring new locations in order to find better seeing. In the hills just south of Rethymnon I found reasonably good seeing (~ 0.8 arcsec) on two out of four nights, and the one night I spent on Sklopa near Chania the seeing was also good. The below image is from Sklopa, a slightly risky location perhaps, since photography is prohibited near the airport and military base. Captured on Sep 3, 2011, at 01:52 UT.

First Jupiter of the season

I got up early this morning to capture this view of Jupiter and the moons Ganymede (close to the planet) and Io. Conditions were quite good, with a NW breeze coming in from the sea and a DIMM seeing of around 0.8 arcsec. Captured at 30 fps, 1600 of 3600 frames stacked in Registax 6. I kept the processing very light to keep a natural appearance. 

More about the jet stream

The following figure is modified from Bely (2003): "The design and construction of large optical telescopes". I added Tenerife and my location (Crete), with the approximate values for the annual jet stream intensities. In fact none of the locations appear to be in particularly good locations with regard to the jet stream; the weakest jet stream is found either near the equator or near the poles. The well-traveled astrophotographer and biologist Jean Dragesco speaks highly of the seeing in equatorial Africa in his book "High resolution astrophotography", and laments the fact that there are no observatories there. My latitude seems particularly bad, but as we saw in the previous post, perhaps the jet stream isn't the big seeing killer after all. 

"Sixteen-year statistics for the wind velocity at an altitude corresponding 
to a 200-millibar atmospheric pressure as a function of latitude in December 
and June. The vertical bars represent the variation in longitude, the solid 
line is for longitude 0, and the dashed line for longitude 180◦" (from Bely 2003). 

The Jet stream, how important is it really?

It is a well known among amateur (and professional?) astronomers that the jet stream is important for the seeing. Or is it? What evidence exists to support this important role of the jet stream? Vernin (1986) reported a good correlation between the wind speed at the 200 milibar level (the jet stream) and seeing at Mauna Kea and La Silla, and suggested that a jet stream speed of less than 20 meters/second was a requirement for good seeing. 

 

Later studies have however cast serious doubt on this; a large quantity of data from various observatories shows a poor correlation between seeing and jet stream speed. Good seeing can apparently be experienced even under a strong jet stream.  The seeing estimates below were made using the DIMM method.

  

Data from Vernin 1986: Astronomical Site Selection - A New Meteorological Approach, Bounhir et al. 2009: High-altitude wind velocity at Oukaimeden observatory, Tokovinin et al. 2003: Statistics of turbulence profile at Cerro Tololo, and Garcia-Lorenzo et al. 2009: Adaptive optics parameters connection to wind speed at the Teide observatory.

My own seeing estimates also show only a slight correlation (actually non-significant; P=0.06) relationship between the seeing (visually estimated, Pickering scale) and the speed of the jet stream. 

There does however seem to be a relation between the coherence time (the “speed” of the seeing) and the jet stream speed.

The above graphs, modified from Garcia-Lorenzo et al. 2009, indicate the necessary exposure time to “freeze” the seeing at a given wind speed at the 200 mbar level (top) and at ground level (bottom). The corresponding frame rate for a video capture is shown on the right Y-axis. The correlation is not high, but in general higher wind speeds, both at ground level and in the jet stream, correlate with shorter coherence time. To match the shorter coherence times at high wind speeds, frame rates above 200 frames/sec (fps) may be necessary. The popular Imaging Source cameras using the Sony ICX098BL chip can achieve only 30 fps without artefacts. Their new model with the Sony ICX618ALA chip can reach 60 fps. The Flea3 from Point Grey can reach 120 fps (possibly with artefacts), or more with ROI (Region Of Interest). The very short exposure times that come with such high frame rates can only be used on a very bright target (e.g. Venus, Mars, the Sun), or with a telescope setup with a low effective focal ratio. 

The wind throughout the whole column of air affects the seeing, as this profile of turbulence shows:

As we see the wind at ground level is more important than the jet stream (notice the logarithmic scale). 

Moons, spokes, and a storm

Here's a couple of old animations. First, Jupiter from November 2010, with Europa on the right and Io appearing out the the shadow on the left. The animation was done by fellow Cloudynights member MvZ, and was featured in Wired. It is one of the best (series of) images I have achieved with my trusty old Toucam Pro web camera. 

 

Click for original size

Next is Saturn, captured with my new DBK21 camera in Mar 2011. The great storm of 2011 is visible in the northern hemisphere. At the left side spokes are visible as dark patches on the rings. For some reason spokes seem to occur most often on the "morning" side of the rings, that is, where the rings rotate out of the shadow from the planet. The new camera does make it easier to get quality images, but still the quality of the seeing is a critical factor; if the seeing is bad both cameras will give bad results. 

  

Estimating the seeing

Astronomical seeing refers to the stability and clarity of telescopic images at high magnification, not to be confused with transparency. Seeing degradation is mainly caused by layers of air having different temperatures. Wind shear produces turbulence that mixes these layers. The seeing can be estimated in many ways; with instruments and specialized software, or by eye through a telescope. William H. Pickering (1858-1938) developed the Pickering scale using a 5-inch refractor, and Damian Peach has made a very nice set of animations illustrating the appearance of a star at each step of the 10-step scale. The size of the telescope aperture and its secondary obstruction will have an effect on the star image; the larger the aperture the better it will show atmospheric turbulence; i.e. a seeing rated 6 through a 5 inch aperture will probably look more like 3 to 4 through 10 inches of aperture. Thus, Pickering seeing estimates between different telescope sizes are not really comparable, unless the observer stops down the aperture to 5 inches, or compensates by guessing what the seeing rating would have been through a 5 inch aperture. Today many amateur astronomers use apertures larger than 5 inches. I made a "new" Pickering scale for a 10 inch telescope, with some Saturn images and a few absolute seeing measurements (in arc-seconds), made with the software DIMM Seeing monitor during its 30-day trial period. I hope in the future to able to fill some of the gaps with more seeing measurements. The star images where simulated with Aberrator. 

Click for original size


In 2002 and 2003 I made many seeing estimates. Seeing better than 6 is nearly unheard of where I live, but at nearby hilltops the seeing does once in a while get as good as 7-8. Catching good seeing is a matter of being in the right place at the right time. 

Open night at the observatory

Have you ever wondered what Saturn would look through a really big telescope? Yesterday I saw Saturn through the 1.3 m telescope at the Skinakas observatory. They had one of their Open Days, and for once the target was not the full Moon. Unfortunately the seeing was not so good (it was difficult to see the Cassini division), but it was a chance for me to see the true colors of Saturn. Through my own puny telescope the colors of Saturn are rather dull, but through the 1.3 m the globe had a distinct straw yellow color. This Voyager 2 image is close. 

 

Looking at Saturn through the 1.3 m telescope

I reprocessed my recent Saturn image to resemble the color I saw through the large telescope: 

Most amateur astronomers tend to process their Saturn images to have far more blue. 

Starmus astrophotography competition

The winners of the Starmus contest were announced a few days ago. The overall winner, Alex Cherney, of Victoria, Australia, will get an all expenses paid trip to the conference, and 1 hour of observing time at the Gran Telescopio Canarias, one of the largest telescopes in the world. I wonder what he will select to observe. I would have chosen Saturn, as it is now placed well in evening sky. 

My own contributions did not make it to the top. Here they are, my best solar system images from a decade of imaging (only Neptune is missing), and an animation of Jupiter occulting the star Cap45. 

 

Untitled from Jon Kristoffersen on Vimeo.

This phenomenon is extremely rare. Few people seem to have captured the occultation on video, and even fewer in visible light. The video may be unique in that it shows  the bright flashes in three bands (red, green and blue) simultaneously. 

  

Welcome

Welcome reader!
This is my first try at a blog, and I have a lot to learn about Blogger. I plan to post my planet images here, and we'll see where it goes from there. For now, here is my latest Saturn image. 

Compared to my first Saturn image from abut a decade ago, it is an enormous improvement. 

I hope one day to equal the results of Damian Peach, whose results are unsurpassed in the amateur astronomy community, see for example this fantastic Saturn image: http://www.damianpeach.com/sat11/2011_03_28lrgb.jpg