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Venus and the NASA Solar Dynamics Observatory (SDO)

Mark Alonzo
This week we got images of Venus tracking across the sun directly in our field of view, courtesy of NASA.  This is a once in a lifetime event, as the next occurrence of this transit won’t happen until 2117.  Of course, with health care advancing the way it is, living another 105 years is actually becoming a reality rather than a highly exceptional event, but I digress.  I actually didn’t know much about the NASA Solar Dynamics Observatory Mission, so I did a little research and I prepared this nice book report for you, my dedicated fans. [gallery] Figure 1:  Images of Venus crossing the sun from several SDO Instruments First, let’s look at some interesting facts about Venus.  On June 5, 2012 Venus floated across the face of the sun over the span of about 6 hours and 40 minutes.  Venus has a mean orbital velocity of 35.02 km/s, as compared to 29.78 of the earth, has a diameter and density of about 95% of the Earth’s, and a mass of about 81% of the Earth’s.    Venus has a 2802 hour long day, compared to our measly 24 hours.  Venus has a completely different atmosphere from ours, comprised mostly of Carbon Dioxide (96.5%) and Nitrogen (3.5%), with much smaller amounts of Sulfur Dioxide, Argon, Water, Carbon Monoxide, Helium, and Neon (maybe that explains it’s bright night time glow ;)   Venus’s atmospheric pressure is about 92 times greater than Earths and its average surface temperature is 740K (467° C, 872° F), enough to cook a full chicken in about half a second.  But who’d want to eat it since it’s probably raining sulfuric acid on you anyways. Ok, enough about the stats of Venus.  What I really want to talk about is the NASA Solar Dynamics Observatory, the instrument that captured all these cool images.  The SDO is a geosynchronous satellite, stationed directly above its ground station in New Mexico, to which it downloads about 4 terabytes of data every day!  The SDO contains a suite of instruments that will provide observations leading to a more complete understanding of the solar dynamics that drive variability in the Earth's environment. This set of instruments will:
  • Measure the extreme ultraviolet spectral irradiance of the Sun at a rapid cadence
  • Measure the Doppler shifts due to oscillation velocities over the entire visible disk
  • Make high-resolution measurements of the longitudinal and vector magnetic field over the entire visible disk
  • Make images of the chromospheres and inner corona at several temperatures at a rapid cadence
  • Make those measurements over a significant portion of a solar cycle to capture the solar variations that may exist in different time periods of a solar cycle
There are three main instruments: HMI, AIA, and EVE. HMI (Helioseismic and Magnetic Imager) looks at the outside of the Sun to try and determine what is happening on the inside.  The Sun has billions of tiny ripples that are a little bit like shocks from an earthquake. They are caused by the Sun's convection zone. HMI will measure the ripples and the magnetic field on the visible surface of the Sun (the photosphere) using different colors or wavelengths. Since we can't actually go to the Sun to study it HMI will use color to measure the Sun's magnetic field. With all the information we gather using HMI about what is happening on the surface of the Sun, Scientists will be able to figure out what is going on inside and making all the cool stuff happen on the outside!  To view more on this instrument, please view this video. Figure 2:  Here are typical HMI data products. AIA (Atmospheric Imaging Assembly) will image the outer layer of the Sun's atmosphere, the corona, at all temperatures from 20 thousand to 20 million degrees. With high time resolution and a view that covers the entire visible hemisphere of the Sun, for the first time the evolution of all energetic solar events will be followed---from the original micro instabilities through the ejection of billions of tons of material into interplanetary space, to the bright flaring in the corona as the magnetic field is reconfigured in the biggest explosions in the solar system. Four telescopes with two passbands each will provide eight full-Sun images every ten seconds, twenty four hours a day, and seven days a week. Figure 3:  A typical AIA image highlighting coronal activity EVE (Extreme Ultraviolet Variability Experiment) is made up of several small instruments. EVE has to keep track of the extreme ultraviolet (EUV) rays that the Sun sends towards us. Ultraviolet (UV) rays are light, like any other light, but of colors that our eyes can't see. UV rays are what can cause skin cancer if we sit out in the Sun for too long over many years with no protection. Extreme ultraviolet rays are even more dangerous, but we on Earth are safe because EUV rays are completely absorbed high up in the Earth's atmosphere. The brightness of EUV light from the Sun changes when the magnetic field of the Sun is more active (like when the Sun spits particles and radiation towards Earth). Scientists want to have a better understanding of why and how the amount of EUV light from the Sun changes. It is EVE's job to help them figure it out. EVE is going to use color (different wavelengths), just like HMI and AIA, and will measure the amount of light in different EUV colors coming from the Sun. EVE will measure a spectrum every 10 seconds 24 hours a day! These measurements will help scientists predict the amount of EUV coming towards Earth at any time based on the activity of the Sun's magnetic field. Figure 4:  Typical data product from EVE sensors Not only do I think the science behind all of this is completely cool, but I was incredibly pleased to see that on the LASP EVE data sight, you can download not just the data but also IDL .sav and .pro files (compiled source code and raw source code for you novices) allowing you direct access to the data and tools in IDL for working with this type of data.  The IDL files can be found here:  http://lasp.colorado.edu/home/eve/data/data-access/ As I dove even deeper I came across SolarSoft, an IDL based application and software library for programming and data analysis for solar physics. Yes, yes, I work for the company that makes IDL so I should know about all this right?  Well, I can’t keep my finger on all of the projects that go on out there and I just thought it was really cool how quickly I came across IDL on my little research project.  I hope you have as much fun looking through all this as I did! P.S. Thanks to NASA from whom I borrowed a lot of this text.

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