What shapes are things in Outer Space?
May 1 2018, 09:00
Last week I was contacted by Gizmodo, who were looking for contributions to their 'Giz Asks' series on the question 'What shapes are things in Outer Space?'. This is how I began my response:
Most things in space—in particular, stars, planets, black holes
and large asteroids—are spherical in shape, like a
basketball. This is because the dominant force at the immense scales
in space is gravity. For any sufficiently massive object, self-gravity—the gravitational pull of each part of the object on the other
parts of the same object—tends to mold the object into the most
compact form, and that happens to be a sphere.
Read my complete answer in the article, along with great write-ups by a number of other astronomers.
A Sterling Hall landscape for Stellarium
Apr 30 2018, 13:44
As one of the components of the upcoming Astronomy 103 Online course, which will be running for the first time in Summer 2018, I've been creating a set of virtual planetarium tours using the popular (and free) Stellarium software. To provide students with a degree of immersion, I customized the landscape with a 360-degree panoramic image from the rooftop of Sterling Hall, home to the Department of Astronomy. This image was created by the awesome (and also free) Hugin panorama stitcher, from 8 separate photographs obtained using a Canon PowerShot ELPH 300 HS camera (although cell-phone cameras can now take impressive shots, I think traditional cameras still provide a superior result).
To try out the the image yourself, first download the landscape zip file. Then, in Stellarium, open up the View dialog (F4), select the Landscape tab, click on the Add/remove landscapes button, and then click on the Install a new landscape from a Zip archive button. Select the file you downloaded, and the Sterling Hall view should appear!
GYRE 5.2 released
Apr 26 2018, 21:00
A few days ago, I released version 5.2 of my GYRE oscillation code. This is the sixteenth release of the code, and coincided with the successful launch of NASA's Transiting Exoplanet Survey Satellite (TESS). I'm hoping that GYRE will become the standard tool for analyzing TESS observations of stellar oscillations; certainly, over the past few weeks, I've noticed an uptick in the number of new users at the GYRE Forums, with the total number of registered users now approaching 100. Exciting times are ahead!
So, what's new in version 5.2? Most of the significant changes have taken place deep in GYRE's internals, with much-needed improvements to speed and stability. Users will notice a few bug fixes, but the next big leaps in functionality — new algorithms for finding highly non-adiabatic modes, and the ability to model dynamical tides — will have to to await the release of GYRE 6.0, later in 2018.
MESA IV: Convection, Diffusion and Explosions, Oh My!
Oct 20 2017, 16:14
Last week I was out in Santa Barbara, working with other developers on finalizing the 4th MESA instrument paper (see here, here, and here for the first three instrument papers). My contribution to this 63-page tome center around the correct treatment of convective boundaries. I've been working on this topic since the KITP Massive Stars program in Winter/Spring 2017, when my friend and colleague Anne Thoul got me interested. Since then, Anne and I have developed a new predictive mixing scheme, which fixes previous issues in MESA with the location and growth of convective boundaries.
As well as describing the predictive mixing scheme, the instrument paper introduces new capabilities for treating elemental diffusion under degenerate conditions, and for modeling core-collapse supernovae. The paper was submitted to the Astrophysical Journal earlier this week, and will appear on the arXiv next week.
Compiling ffmpeg on OSX
Jun 15 2017, 15:19
While rolling a new release of the MESA SDK, I've finally stumbled on the magical invocations necessary to compile the ffmpeg video encoder/decoder on recent releases (10.10 and beyond) of Mac OSX. The problem lies with headers for various OSX frameworks, which cause the gcc compiler to barf. The solution is to disable usage of these frameworks when configuring ffmpeg; specifically, configure with the following flags:
./configure --disable-videotoolbox --disable-audiotoolbox --disable-vda
I've not seen this workaround elsewhere on the web (almost all discussions of ffmpeg on OSX focus on homebrew installation); so, I thought I would post it here in the hope that someone might benefit.