Category Archives: Astronomy

Cassini End of Mission

After twenty years in space (launched 10 years Bi, Before iPhone), traveling over a billion KM, and returning data for 13 years from more than a light-hour from Earth, the Cassini Spacecraft ended its mission this week.

The project has accomplished lots of amazing science, represented by 3,948 papers so far. There will surely be a few more—lets go for 5K papers!

The end was a planned dive into the atmosphere of Saturn, collecting a few more bits of data on the way down, and assuring the complete destruction of the spacecraft.

As has been explained before, the spacecraft needed to be vaporized to prevent even the slighted chance that it might contaminate the area with Earth microbes. Aside from not wanting to harm any life that might exist on the moons or dust, we also don’t want to accidentally leave something that a later spacecraft might find and not realize was inadvertently sent from Earth.

(Which, if you think about it is way, way cool. How many human endeavors have to worry about the possibility of contaminating alien ecosystems, even in principle?)

Hence, the final dive.

This montage of images, made from data obtained by Cassini’s visual and infrared mapping spectrometer, shows the location on Saturn where the NASA spacecraft entered Saturn’s atmosphere on Sept. 15, 2017. Credit NASA/JPL-Caltech/Space Science Institute

Cassini signed off permanently on September 15. Loss of Signal. End of Mission. Lots of accomplishments.


Space Saturday

Cool NASA Imagery of Solar Eclipse

The total eclipse was spooky and cool, and an opportunity for science and nerdism to rule.

The experiences and reports on the ground were awesome. But NASA is observing the Earth in a lot of ways and from a lot of angles that are not on the ground. And they release some really cool examples from Monday.

As they put it, “So Many Ways to View an Eclipse”.

They have several time lapse compilations that show the shadow of the moon racing across the Earth.

I love this one because the circular shadow is so clear to see.

The eclipse also showed up in other traces, including temperature maps, views of the top of the atmosphere, and, of course, images of the sun.

Science Rulz!

  1. NASA Earth Observatory, So Many Ways to View an Eclipse, in NASA Earth Observatory 2017.


Space Saturday

Dark Energy Survey Reports

The Universe we live in has a lot of matter and energy in it. We can see and measure matter and energy, but it is now clear that we can see only about 2% of what is there. We can tell that there is a lot of matter and energy out there that we simply cannot measure, it is called Dark Matter and Dark Energy. The universe is about 26% Dark Matter, and about 70% Dark Energy. What is all this Dark stuff? No one knows, but we sure need to find out, right?

Since 2013, a global collaboration of astronomers has been systematically surveying the sky to confirm the existence and assess the amount of Dark Energy. The Dark Energy Survey  is a heroic project, using a large telescope facility in the high desert of the Andes to spot and measure supernova. A massive amount of data is collected each night and stored in digital images.

The data is transferred through an optic fiber channel that runs up the spine of the America’s to Illinois, right down the street from where I sit. The data is organized into the archive, which is analyzed by science teams around the globe. It takes hours to transfer each night’s (irreplaceable) data to the data center, every day.

This summer, the DES is releasing a burst of ten papers to report the first year’s results [1]. (It has taken several years to analyze the first year’s data.  Unlike Hollywood movies, real life data analysis is hard work and takes time.)

The details of these analyses are largely beyond my own understanding, though I understand very well the scale of the computation and the system engineering this has required: this project is trying to measure the whole sky, and is looking for brief events that must be zoomed into. “Challenging” doesn’t begin to describe it.

Glancing through the papers, it is clear that this massive effort is yielding pretty solid results. To pick one paper arbitrarily, “Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Sheardiscusses one important thrust of the research, attempting to document the actual expansion of the Universe, and to improve estimates for the infamous cosmological constant that represents the “anti gravity” effects of Dark Matter and Energy.

The report itself is attributed to 135 authors from 51 institutions, and is based on observations of 36 million galaxies. The bulk of the paper describes the (complex) methods used to assemble and interpret the observational data. The results are close to earlier estimates of cosmological parameters from much smaller datasets. Results from other studies in this batch combine with these to tighten the estimated bounds on these values.

It’s all overwhelming, but as the authors dryly note, we really have no understanding of these fundamental facts yet. These are deep and fundamental mysteries, and we really need to know. The DES is an important step in understanding our universe.

Despite the overall success of modern cosmological study, however, there remain several fundamental mysteries that enter the model as purely phenomenological parameters. These include our lack of understanding of the value of the cosmological constant or of any motivation for a different driver of cosmic acceleration.” (p.2)

  1. The Dark Energy Survey. DES Year 1 Cosmology Results: Papers. 2017,
  2. The Dark Energy Survey. Home – The Dark Energy Survey. 2017,
  3. M. A. Troxel, N. MacCrann, J. Zuntz, T. F. Eifler, E. Krause, S. Dodelson, D. Gruen, J. Blazek, O. Friedrich, S. Samuroff, J. Prat, L. F. Secco, C. Davis, A. Ferté, J. DeRose, A. Alarcon, A. Amara, E. Baxter, M. R. Becker, G. M. Bernstein, S. L. Bridle, R. Cawthon, C. Chang, A. Choi, J. De Vicente, A. Drlica-Wagner, J. Elvin-Poole, J. Frieman, M. Gatti, W. G. Hartley, K. Honscheid, B. Hoyle, E. M. Huff, D. Huterer, B. Jain, M. Jarvis, T. Kacprzak, D. Kirk, N. Kokron, C. Krawiec, O. Lahav, A. R. Liddle, J. Peacock, M. M. Rau, A. Refregier, R. P. Rollins, E. Rozo, E. S. Rykoff, C. Sánchez, I. Sevilla-Noarbe, E. Sheldon, A. Stebbins, T. N. Varga, P. Vielzeuf, M. Wang, R. H. Wechsler, B. Yanny, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, K. Bechtol, A. Benoit-Lévy, E. Bertin, D. Brooks, E. Buckley-Geer, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, M. Crocce, C. E. Cunha, C. B. D’Andrea, L. N. da Costa, D. L. DePoy, S. Desai, H. T. Diehl, J. P. Dietrich, P. Doel, E. Fernandez, B. Flaugher, P. Fosalba, J. García-Bellido, E. Gaztanaga, D. W. Gerdes, T. Giannantonio, D. A. Goldstein, R. A. Gruendl, J. Gschwend, G. Gutierrez, D. J. James, T. Jeltema, M. W. G. Johnson, M. D. Johnson, S. Kent, K. Kuehn, S. Kuhlmann, N. Kuropatkin, T. S. Li, M. Lima, H. Lin, M. A. G. Maia, M. March, J. L. Marshall, P. Martini, P. Melchior, F. Menanteau, R. Miquel, J. J. Mohr, E. Neilsen, R. C. Nichol, B. Nord, D. Petravick, A. A. Plazas, A. K. Romer, A. Roodman, M. Sako, E. Sanchez, V. Scarpine, R. Schindler, M. Schubnell, M. Smith, R. C. Smith, M. Soares-Santos, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, D. Thomas, D. L. Tucker, V. Vikram, A. R. Walker, J. Weller, Y. Zhang and (DES Collaboration), Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear. The Dark Eneergy Survey, 2017.


Checking in with Cassini

The Cassini spacecraft has completed 5 of its 22 final swoops, conducting a feverish rush of observations on the outbound segment.

This science program was the product of long planning and discussion, to try to jam in as much science as possible, and to take advantage of the unique opportunities of each minute of each orbit. (If you fly all the way to Saturn, you want to get as many pix as possible, no?)

One observation peered at close range at one of the rings for its entire 14 hour rotation around Saturn, to get a detailed record. Another observation observed an occultation of Sirius by Saturn’s atmosphere, data not available from any other available method.

Cassini also took close up (well, from 168,000 KM), 1KM per pixel images of my new favorite moon, Enceladus. We’re on our way, Encie!

Credit NASA/JPL-Caltech/Space Science Institute

This week also saw and episode that gives perspective to just how far out at the edge of the possible Cassini is flying. The spacecraft is tiny and far away, and communicates via the Deep Space Network. Like many people who have fussed about with computer networks, I consider the DSN as nearly miraculous. It is a tribute to its designers and operators that we take for granted that we will be able to up and down link our spacecraft, even out at Saturn and beyond. (We are not worthy!)

Nothing is perfect, and like all engineering, end-to-end issues ultimately rule. This week some of the data downlinked from Cassini was lost because of heavy rains in Australia. First of all: rain in the desert? What’s the deal with that?.   Second: we are all thankful for the blessing of rain on that parched continent.

The problem, of course, is that the signals from Saturn are weak and far away. The natural radio noise from a rainstorm is not gigantic, but is sure is close, and (literally) drowned out the downlink.

The downside of one-of-a-kind observations is that and error or loss is unrecoverable. That data will never be seen.

As I said, rare problems serve to highlight just how robust the DSN has been for decades now.

Cassini continues to roll along, working like mad right up to the end in September.

  1. Cassini Science Communications Team. Cassini Significant Events 5/17/17 – 5/23/17. 2017.


Space Saturday

Astronomy Leads The Way In Big Data

Jay Kremer and colleagues at University of Copenhagen write in IEEE Intelligent Systems about, “Big Universe, Big Data: Machine Learning and Image Analysis for Astronomy [1].

This article is a nice survey of the kinds of data that astronomers collect, and the challenges of analyzing, and, indeed, simply handling it all.

I have worked with Astronomers in the past, and one of the coolest things is that when they have a dataset that covers “everything”, they really mean everything—the entire Universe, at least as much as we can see from where we are. And it is so romantic. Every study deals with space and time, matter and energy, theory and observation. Astronomical data makes you feel tiny and insignificant. Yet we are part of this gigantic picture, and our brains are capable of learning so much about it.


Kramer walk through many aspects of  contemporary Astronomical data. They describe the data (visible light and spectrographic measures), which are captured in detailed images of the sky. Billions of pixels recorded from signals that have travelled incomprehensible distances over inconceivable time spans, to intersect with us here and now.

No human could view all this information, nor make sense of it. The data is run through pipelines that use algorithms to clean up the data and look for “interesting” stuff. These days, the processing also automatically generates catalogs of objects in the image, i.e., tries to find everything interesting in the image. Of course, the details depend on the data source and what you are looking for—stars, galaxies, planets, asteroids, or many other possible targets.

Over the years, astronomers have employed all kinds of image analysis, including machine learning techniques to automate these processes. In fact, many techniques pioneered by astronomers have been adopted for other uses. Astronomers have also pioneered the use of crowdsourced “citizen science” to aid the development and validation of these algorithms. Galaxy Zoo was one of the first and most successful such citizen science project, and has spawned dozens of clones.

In order to understand and answer questions about these massive datasets, e Astronomers have also pioneered statistical methods and search techniques. Kramer also discusses the difficult challenges of creating models that connect theory to the observational data. Much of astronomy is about trying to go from theoretical physics to “pixels in the image”, and vice versa.

Finally, they note that most of the data is openly available (though you really can’t download a copy, because it too freaking much). Most of the software is available, too. (This openness is possible largely because no one knows how to make money off astronomy, not even astronomers.) This means that there is opportunity for anyone to get into the game, to create new analyses, or to discover new science. Much of the data has hardly been studied at all, so who knows what you might be able to do?

In one sense, this article is nothing new. For centuries, Astronomy has led the development of instruments, data analysis, and theory. Looking out at the universe is both the hardest, and the most informative, scientific observations of all, and Astronomers are always working at the edge of what is technically possible.

In the past few years, there has been an accelerating trend to cut pubic funding for scientific research. The remaining funds are ever more tightly rationed, forcing hard choices, and difficult arguments about the relative benefits of different activities. Inevitably, there are strong pressures to reduce activities that have little obvious and direct benefit for people or important political interest groups.

One of the prime targets has been large-scale astrophysics, which requires expensive equipment and is, by definition, not about current life on Earth. It doesn’t even employ large numbers of people, at least once construction has finished. What good is it, except to fill the curiosity of a few egg heads?

This political picture is important to keep in mind when reading this article. They are responding to the “Why should we pay for these large investigations?”

In short, one reason to support Astronomy research is that this work can drive many data technologies that are increasingly important in may fields closer to home (and more profitable).

This is not the most romantic reason to do Astronomy, but it is a valid and important point.

  1. Jan Kremer, Kristoffer Stensbo-Smidt, Fabian Gieseke, Kim Steenstrup Pedersen, and Christian Igel, Big Universe, Big Data: Machine Learning and Image Analysis for Astronomy. IEEE Intelligent Systems, 32 (2):16-22, 2017.


Space Saturday

Cassini Making First Ring Grazing Pass

This week he Cassini spacecraft will zip past the outer rings of Saturn, gathering very close up imagery of this region for the first time. If all goes as planned, there will be 30 orbits, before Cassini is steered into a final dive into the atmosphere to end the mission.

Earlier this week the mission released some images that show Saturn from the rarely seen angle. The images portray the strangely hexagonal jet stream at the North pole.

this collage of images from NASA's Cassini spacecraft shows Saturn's northern hemisphere and rings as viewed with four different spectral filters. Each filter is sensitive to different wavelengths of light and reveals clouds and hazes at different altitudes. Credits: NASA/JPL-Caltech/Space Science Institute
this collage of images from NASA’s Cassini spacecraft shows Saturn’s northern hemisphere and rings as viewed with four different spectral filters. Each filter is sensitive to different wavelengths of light and reveals clouds and hazes at different altitudes. Credits: NASA/JPL-Caltech/Space Science Institute

This weird looking phenomenon has been observed for several decades (i.e., it is really there and it is pretty stable), and, as far as I can tell, isn’t clearly understood. Presumably, the pattern results from the rotating winds in Saturn’s giant atmosphere, but just how it might come about is still being debated.

Anyway, let’s stay tuned for some close ups of the rings—surely one of the most spectacular tourist attractions in our solar system!

(PS.  Wouldn’t “First Ring Grazing Plunge” be a great name for a band? )


Space Saturday

Cassini to visit the rings

I didn’t know that Cassini was still active out at Saturn. It’s been out there more than a decade now, exploring the spectacular ringed planet and its amazing collection of moons. I thought the mission was long over.

Not so!

Cassini is still alive, and about to enter its last orbits, swooping in closer than ever before the final dive into the atmosphere next September. Wow!

Starting later this month, Cassini will graze by and image the outer rings and also fly low over the atmosphere. In subsequent orbits, the spacecraft will attempt to sample dust and gas as it passes the rings.


We’ll stay tuned for unprecedented close ups from the famous rings of Saturn.


Space Saturday