Still Holding

Clouds and wind have conspired to bring this project to a screeching halt.

I'm seriously considering getting more into radio astronomy.

Clear and Windy

Nothing much to update.  It's been mostly clear this past week, but also windy.  Wind bumps the scope around too much which makes for useless data.  I now have an even greater appreciation for domed observatories.

Saturn at opposition yesterday, 177 degrees away from the sun.

It's about time that I start to make the plots of the data I actually want to see: brightness versus orbital phase.  Stay tuned for that.

Seeing Effects

Had a great session last night -- the first night in nearly two weeks!  My prediction that I'd get about half of the nights was very far off.  Sofar, since my Jupiter work started on 12 Feb 2014, I've had 14 observing sessions.  So that means that my "observing efficiency" is at 17.5% (14 / 80).

The surprise this evening was the seeing.  Towards the end of the session, I turned the scope to Saturn to start collecting 300 images of prelim data (I'm still assessing whether I can get "good enough" signal to noise to make the effort worthwhile) when just a little breeze blew through.  The breeze was enough to notice but it was brief and, I thought, uneventful.

However, this little breeze brought with it some nasty air!  The seeing went from really good to really bad in a matter of a couple minutes.  Check these images out of Saturn:

Figure 1: Saturn in good seeing and in bad seeing, minutes apart

Having high-resolution astronomical imaging in my background, I'm curious about these things and would like to understand them better.  I don't recall ever witnessing the seeing deteriorate so quickly.  I'd like to know what exactly causes this and how long it lasts.

I can't make a post to this blog without a nice picture of the Jupiter system from last night:

Figure 2: The Jupiter system 03:09 UTC 03 May 2014

Also some nice Jupiter moon events for May:

5/8     E eclipse R     04:06

        I eclipse R     05:52
5/11    I/E close       04:00
5/17    I/G/C close     04:00
5/18    I/E/C close     05:00
5/24    G eclipse R     03:31
        I eclipse R     04:10
05/26   C eclipse D     04:39

Great Photometry

Looked at the data from 17 March 2014 UTC today and found it to be very clean.  Io and Ganymede were making a close approach to one another, so their light is combined in the plot below:

Figure 1: Photometry for 17 March 2014 UTC

In any case, this data looks really nice and I'm happy with the data collection and calibration process.  This data is now what I'd call "fully calibrated" in that the final "reduction" is now complete with respect to atmospheric extinction.  X-axis is the UTC time, and the y-axis is the brightness, in ADU (corrected such that this would be the brightness at the top of the atmosphere).

Surprise color, Saturn here I come

What does it mean when the atmospheric extinction is different for each moon of Jupiter?

Figure 1: Linear fit to compute Atmospheric Extinction

It means (as far as I can tell) that I'm seeing COLOR DIFFERENCES between the moons.  Very very cool.

In Figure 1, the x-axis is the sec(Z) value, and the y-axis is the photometric value (in ADUs).  The relationship between these two values is linear with a negative slope (objects get fainter as they get closer to the horizon).  But the fact that there are differences between the slopes for the different moons can only mean that I'm seeing color differences in those moons.

My system is looking through a 'green' filter:

Figure 2: The filter set I use

So what do the differences in color mean?  Well, I can say that moon A is "redder" or "bluer" than moon B.  But what does a larger or smaller slope mean in terms of color?

The atmosphere absorbs blue light more than red light.  So as the object gets lower and lower to the horizon, more blue is lost, which makes the object appear fainter.  What this tells me is that Ganymede is "bluer" than Europa and Io, and Io is slightly "bluer" than Europa.

The larger the negative slope, the "bluer" the object is.  This is a hard one to visualize, so I may have to correct this statement later.

I noticed all of this in some data I was looking at from 01 April 2014 and noticed these differences.  Since I have to go back and run all my data reduction software again on all the data, I figured I'd stop and take a look at this (and other things) to try to work out how I want to proceed with yet another surprise.

There have now been three surprises:

1. Watching targets move in and out of Jupiter's shadow
2. Watching targets occult or near-miss (I've seen the latter) each other and (I think) seeing a dimming event caused by targets' "atmosphere".
3. Seeing the color differences between the targets

What else is in store for me?  I'm open for more suggestions, Mr. Jupiter.

I am GO for Saturn

I'm very excited to start my Saturn observations.  For starters, there are SEVEN moons to monitor, with orbital periods between 22.6 hours (Mimas) and 1903.7 hours (Iapetus).  They are all tidally locked, so I'll get the same sort of "full disk" view every orbit.  But in this case, the entire system is tilted at an angle of 26.73 degrees to the ecliptic (very similar to ours) which means I'm seeing more of one pole at a time.  Very photometrically dynamic, I would think.  We'll see.

Saturn opposition is 10 May 2014 - 16 days.  I found this interesting article about Saturn and most interesting is this:

Another interesting phenomenon to watch out for near opposition is known as the Seeliger effect. Also sometimes referred to as the “opposition surge,” this sudden brightening of the disk and rings is a subtle effect, as the globe of Saturn and all of those tiny little ice crystals reach 100% illumination. This effect can be noted to the naked eye on successive nights around opposition, and will get more prominent towards 2017. Coherent-backscattering of light has also been proposed as a possible explanation of this phenomenon. Perhaps a video sequence capturing this effect is in order for skilled astro-imagers in 2014.

According to the Wikipedia entry on 'Opposition Surge', the variation can be quite noticeable.

Just the distances involved are pretty awesome.  Jupiter is about 700 million km away.  Saturn is 1340 million km away -- nearly twice as far!

Approximate maximum elongations for the moons:

Mim: 28.6 arcsec (11 pixels)
Enc: 36.6 arcsec (14 pixels)
Tet: 45.4 arcsec (17 pixels)
Dio: 58.1 arcsec (22 pixels)
Rhe: 81.2 arcsec (31 pixels)
Tit: 188.2 arcsec (72 pixels)
Iap: 548.5 arcsec (210 pixels)

Some of those might be tough, but we'll see.  I should see the same "surprises" with the Saturn system as I do with Jupiter.

PLUS, there is the planet itself and those nice rings.  Since I'm not saturating, I should be able to track the lightcurve of these, also.

I think the signal-to-noise is going to be ok with a 0.2 second exposure.  I think any longer exposure will ruin my chances of getting photometry on Saturn itself.  So I'll suffer a bit with the S/N.

Here's a plot showing the signal from Iapetus -- one of the fainter ones for sure:

Figure 3: Signal from Iapetus

And here's another plor showing the signal from Titan:

Figure 4: Signal from Titan

Both of these plots, as you can see, are on the same scale.

I've calculated that the S/N for Iapetus and Titan are 14.7 and 41.5 respectively.  Anything over 10 is good enough for me, but it will be challenging and I'm anxious to see how noisy this data is.

All of this is very preliminary as I collect more data.  I only took 100 images the other evening, and many of those will be garbage.  So at this point I'd guess that I've got maybe 50 data points on this stuff.  More data required to see how it's going to all work out.  As usual, I'll let the data guide me.

More great data and a surprise

I had two nice sessions in the past week -- last 15 April 2014 and yesterday evening 21 April 2014.  Here's a pic from last night:

Figure 1: The Jupiter system 03:25 UTC 21 April 2014

I have a LOT to talk about, but I've been otherwise occupied so a detailed update will continue to have to wait.

The surprise is that I'm very close to deciding that the Saturn system will be my next target.  My expectations were that I might be able to see Titan, but what I actually was able to see blew me away.  Take a look:

Figure 2: Saturn 05:39 UTC 21 April 2014

Iapetus!

Figure 3: The Saturn system 05:39 UTC 21 April 2014

Titan, Rhea, Tethys, and Dione:

Figure 4: The Saturn system

So -- should I start working with the Saturn system?  I probably will.  I need to look carefully at the signal to noise and also see if I can increase the camera exposure time by a little bit to help.

But, at this point it looks like I'll probably start looking at Saturn.  It's in a perfect place in the sky that I'll be able to watch it for the next several months.

More details on Jupiter a little later -- promise.

Unusual Light On Mars

The Curiosity rover on Mars imaged some unusual events the other day.  Here's the link to the NASA press release.

It's most likely that these "raw" images have been calibrated in some way. Normal CCD calibration includes removing cosmic ray events. I would expect that a paper has been published on the calibration procedure for Curiosity (MSL). I'm going to try to find it. Because -- if cosmic ray events are removed, then it's hard to imagine that this is a cosmic ray event.

I've spent quite a bit of time over the years looking at Mars images. I don't recall ever seeing a cosmic ray event on any Mars images, although they clearly should happen very very often (my own experience with astronomical imaging tells me this). Perhaps since these cameras are "hardened" for space, they block most cosmic ray events? I find that theory doubtful.  The NASA people say that cosmic ray events appear on images "nearly every week" but as I said I don't ever remember seeing one.

So I have a hard time with the cosmic ray explanation.

I also can't be too sure about the "glint" theory. Only one of the navcams saw this (the right one). The left navcam image, taken at the same time, shows nothing unusual. Check it out yourself at http://mars.jpl.nasa.gov/msl/multimedia/raw/ Left/Right Navigation Camera, Sol 559, timetag 2014-04-03 10:00:03 UTC. The earlier one is Sol 558, timetag 2014-04-02 09:04:28 UTC. Same thing: right navcam shows the event, left doesn't.

I have no theory as to what this is. I make two additional observations:

Obs 1: These events are 24h 55m 35s apart. A "solar day" on Mars is 24h 39m 35s. A close correlation.

Obs 2: Looking at the two images and blinking between them, it seems to me that whatever it is, it's in the same location on the surface in both images.

However, I can't come up with an explanation as to why a glint would appear in one camera and not in the other. Cosmic rays could, however. But as I said above, I would think that cosmic rays would be filtered out during calibration. Then to have two in as many days doesn't seem likely.

I think they should turn around and take a closer look. They have 30+ years of power, so why not? That rover should live up to it's name and here's a perfect chance to do so.