Title: The Apogee Podcast – IRIS Eyes The Sun
Original Paper: http://arxiv.org/abs/1405.1639v1
Description: In this Apogee podcast, Cosmic discusses the science goals and data acquisition operations of the Interface Region Imaging Spectrograph, otherwise known as IRIS.
Bio: Cosmic is a self- and crowd-funded independent research astronomer and space musician.
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Hello! This is Cosmic, and welcome to the Apogee podcast! This podcast is still relatively new and subject to evolution. For now, the format of this podcast will be myself describing, discussing, and critiquing an article of my choice from an astronomical journal. These podcasts will take place at or near the date of the apogee which is when, along its orbit around the Earth, the Moon is furthest away.
If you have any articles to suggest for future podcasts, I would be happy to take a look at them. I can be reached at cosmiclettuce AT yahoo DOT com.
The music you hear in the background are my own compositions.
I hope you enjoy listening to space music as much as I do. I’ll say more about this particular piece at the end of this podcast.
The apogee for this podcast will take place at 19:11 UTC on 30 June 2014. The lunar distance at that time is 405931 km, which is 976 km further away than last apodee on the 3 June, and 637 km closer than the next apogee on 28 July.
How do we know how far away the moon is?
– observed enough to calculate an orbit
– laser range measurements (light travel time)
Help me measure the distance to the Moon!
On the evening of 5 July 2014, the Moon will appear very close to the planet Mars. At that time, I would like to get some help measuring the distance to the Moon. What I need are pictures of the Moon and Mars taken at approximately the same time from as many different locations as possible.
1. Set your camera up on a tripod for best image quality.
2. Make sure that the picture you take has both all of the Moon and Mars in it,and that the focus is as good as you can make it.
3. Email me the picture along with the time you took it (+/- 5 minutes) and your location (latitude and longitude, +/- 20 miles).
It’d be best if all images could be taken at appoximately the same time. Let’s make this time 04:00 UTC (which would actually make it early morning 06 July in England), which is 21:00 PDT, 22:00 MDT, 23:00 CDT, and 00:00 EDT for the United States.
On with the paper!
I’ve been spending several of the last few minutes looking, once again, and the mezmorizing high-resolution images taken of the sun by one of our latest space-based scientific instruments called IRIS, which stands for Interface Region Imaging Spectrograph.
I started looking at IRIS data a few weeks ago, and I haven’t missed a day going over to the IRIS website (iris.lmsal.org) to look at the latest data. Here, the IRIS team has created a crude (I like crude) but very functional user interface to allow viewing of the data in one of several movie modes. I usually download the mp4 file to my computer and play it on my movie player.
Here are some simple observations I’ve made by just looking at the data:
- The field of view tracks the rotating sun, so there’s no drift
- The image rapidly moves from left to right over and over and over, as if it’s scanning. There turns out to be 49 different “rastering modes” which different types of data can be taken for different types of targets.
- There is a dark vertical line going down the center of the images, it also moves rapidly from left to right. This is the slit for the spectrograph. Brilliant! The primary mirror is used as the entry slit for the spectrograph! No light in that region is reflected, of course so it appears black.
- Every once in a while, there’s a shower of very bright flashes that cover and even overwhelm the solar image. Obviously some kind of electrical activity, but I have no explaination as to what the natureof this activity is.
- Three basic data types, one engineering type. The first data type that I’ve seen are stellar calibration images. It turns out that there are a number of stars that are pretty bright in the ultraviolet regions of the spectrum. IRIS can see these and therefore calibrate the photometry and spectroscopy coming from the sun to absolute terms. The 2nd data type are limb shots where usually prominences are numerous. It’s spectacular to watch these move, and trace the motion of material along invisible magnetic field lines, fountains stretching up from the sun and then dropping back down, and material streaming off the sun in small and large mass ejections. The 3rd type of data I see are usually centered on sunspot regions with the intent of waiting for flares to erupt. In the meantime, the motion and change is contant and very dynamic. And not only is everything in motion, everything is also changing in brightness and color, as evidenced by the equally dynamic spectra. The engineering type just checks systems for throughput.
IRIS is collecting near and far ultraviolet images and spectra of regions of the sun called the photosphere, chromosphere, transition region, and the corona. Because this place is so dynamic, it is hardly understood at all. The purpose of this project is to collect data that will hopefully allow us to better understand exactly what’s going on in these regions.
What’s needed is as much imaging in as many wavelengths as possible, along with spectroscopy at selected wavelength bandpasses which highlight the areas of the sun that are being investigated.
IRIS is such a device. With a single and very small 19cm telescope and some very very clever optics, IRIS can produce high-resolution images at four different wavelengths sumultaneously, while also producing three spectral regions containing a total of 12 high-resolution spectral lines.
How high-res is IRIS? For images, how about 0.33 arcsec pixels? At 1 AU, this corresponds to a pixel size of 240 km. The spectrometer has a resolution of 26-53 milli-Angstroms. This is enough to allow us to see changes is speed as “slow” as 1 km per second.
The paper that I’ve referred to for more information has been the paper on the IRIS website entitled “The Interface Region Imaging Spectrograph (IRIS)”. In it, the authors discuss the complexity of the chromosphere and transition region in more detail and underline the fact that these regions are not very understood. How is all that energy and material moving from the surface of the sun (the photosphere) to the corona and then beyond as the solar wind or a CME?
They then go into a set of three questions that they would like to answer with the data they’re now collecting with IRIS:
The first is “Which type of non-thermal energy dominate in the chromospere and beyond?” The thinking here is that perhaphs there are waves that transport energy through this region. There might also be electical currents transporting this energy. It might also be transported by magnetic reconnection.
The 2nd question is “How Does the chromosphere regulate the mass and energy supply to the corona and heliosphere?” They basically sum up their understanding of this by the statement “the heating of the solar corona and the acceleration of the solar wind remain mysterious.” They’re just gonna have to watch and learn.
The 3rd question is “How does magnetic flux and matter rise through the lower atmosphere and what role does flux emergence play in flares and mass ejections?” Jets, flares, and CMEs have been observed for years and still no one knows what’s causing them. High spacial and spectral resolution will allow us to get some good data on these regions to hopefully better understand what’s going on over there.
They then spend a good amount of time describing the hardware and software on the spacecraft. I will leave it to those who are engineering types to go through all of that in detail on your own. I especially like the automatic exposure control (AEC) system, who’s philosophy it is to make sure that “over-exposed data do not occur too often.”
They also describe their data calibration process, which is extra tricky being out in orbit around the earth and always seeing the sun. Again, I will leave it to those who are interested in the details of the data calibration process to consult section 7 of the paper.
I look forward to seeing what others do with data coming from IRIS. As they come in, perhaps I’ll review one or two in an upcoming Apogee podcast. I also hope to do some of my own research with this data, although to be honest the sun baffles me and I’m not quite sure what yet to take a close look at. So for the time being I’m going to continue just watching those amazing videos.
The music you’ve been hearing in the background is what I call “data music”. In this case, I am “playing” the Magnisium II h spectral line at 2803 Angstroms as I scan the surface of the sun. I calculate the differences between adjacent data values, and then modulate them to fall between the values of 1 and 8. I then chose the ionian musical modality with a base note of C. A value of 1 would correspond to C, a value of 2 would correspond to D, a value of 3 would correspond to E, and so on up the scale to the value of 8 which is one octave above the beginning C. Although it may sound random, it isn’t. This is highly structured information from our sun and interpreted as music. What do you hear?
Until next time, Peace.
End of podcast:
365 Days of Astronomy
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