Do you wonder how astronomers find all those exoplanets orbiting stars in distant solar systems?
Mostly they use the transit method. When a planet travels in between its star and an observer, the light from the star dims. That’s called a transit. If astronomers watch a planet transit its star a few times, they can confirm its orbital period. They can also start to understand other things about the planet, like its mass and density.
The planet Mercury just transited the Sun, giving us all an up close look at transits.
Venus and Mercury have been observed transiting the Sun many times over the past few centuries. When these planets are seen passing between the Sun and the Earth, opportunities exist for some great viewing, not to mention serious research. And whereas Mercury makes transits with greater frequency (three times since 2000), a transit of Venus is something of a rare treat.
In June of 2012, Venus made its most recent transit – an event which will not happen again until 2117. Luckily, during this latest event, scientists made some very interesting observations which revealed X-ray and ultraviolet emissions coming from the dark side of Venus. This finding could tell us much about Venus’ magnetic environment, and also help in the study of exoplanets as well.
For the sake of their study (titled “X-raying the Dark Side of Venus“) the team of scientists – led by Masoud Afshari of the University of Palermo and the National Institute of Astrophysics (INAF) – examined data obtained by the x-ray telescope aboard the Hinode (Solar-B) mission, which had been used to observe the Sun and Venus during the 2012 transit.
In a previous study, scientists from the University of Palermo used this data to get truly accurate estimates of Venus’ diameter in the X-ray band. What they observed was that in the visible, UV, and soft X-ray bands, Venus’ optical radius (taking into account its atmosphere) was 80 km larger than its solid body radius. But when observing it in the extreme ultraviolet (EUV) and soft X-ray band, the radius increased by another 70 km.
To determine the cause of this, Afshari and his team combined updated information from Hinode’s x-ray telescope with data obtained by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO). From this, they concluded that the EUV and X-ray emissions were not the result of a fault within the telescope, and were in fact coming from the dark side of Venus itself.
They also compared the data to observations made by the Chandra X-ray Observatory of Venus in 2001 and again in 2006-7m which showed similar emissions coming from the sunlit side of Venus. In all cases, it seemed clear that Venus had unexplained source of non-visible light coming from its atmosphere, a phenomena which could not be chalked up to scattering caused by the instruments themselves.
Comparing all these observations, the team came up with an interesting conclusion. As they state in their study:
“The effect we are observing could be due to scattering or re-emission occurring in the shadow or wake of Venus. One possibility is due to the very long magnetotail of Venus, ablated by the solar wind and known to reach Earth’s orbit… The emission we observe would be the reemitted radiation integrated along the magnetotail.”
In other words, they postulate that the radiation observed emanating from Venus could be due to solar radiation interacting with Venus’ magnetic field and being scattered along its tail. This would explain why from various studies, the radiation appeared to be coming from Venus’ itself, thus extending and adding optical thickness to its atmosphere.
If true, this finding would not only help us to learn more about Venus’ magnetic environment and assist our exploration of the planet, it would also improve our understanding of exoplanets. For example, many Jupiter-sized planets have been observed orbiting close to their suns (i.e. “Hot Jupiters“). By studying their tails, astronomers may come to learn much about these planets’ magnetic fields (and whether or not they have one).
Afshari and his colleagues hope to conduct future studies to learn more about this phenomenon. And as more exoplanet-hunting missions (like TESS and the James Webb Telescope) get underway, these newfound observations of Venus will likely be put to good use – determining the magnetic environment of distant planets.
On May 9, 2016, Mercury passed directly between the Sun and Earth. No one had a better view of the event than the space-based Solar Dynamics Observatory, as it had a completely unobstructed view of the entire seven-and-a-half-hour event! This composite image, above, of Mercury’s journey across the Sun was created with visible-light images from the Helioseismic and Magnetic Imager on SDO, and below is a wonderful video of the transit, as it includes views in several different wavelenths (and also some great soaring music sure to stir your soul).
Mercury transits of the Sun happen about 13 times each century, however the next one will occur in only about three and a half years, on November 11, 2019. But then it’s a long dry spell, as the following one won’t occur until November 13, 2032.
Four years ago today, the Solar Dynamics Observatory embarked on a five-year mission to boldly go where no Sun-observing satellite has gone before. SDO uses its three instruments to look constantly at the Sun in ten different wavelengths. Called the “Crown Jewel” of NASA’s fleet of solar observatories, SDO is a technologically advanced spacecraft that takes images of the sun every 0.75 seconds. Each day it sends back about 1.5 terabytes of data to Earth — the equivalent of about 380 full-length movies.
SDO launched on Feb. 11, 2010, and it has since captured the amazing views of the ever-changing face of the Sun — the graceful dance of solar material coursing through the Sun’s the corona, massive solar explosions and giant sunspot shows. Enjoy this latest highlight video from year 4 from SDO!
I was priveldged to be able to attend the launch of SDO, and you can read our article about the launch here.
The launch included a little “special effects” that wowed the crowd. The Atlas rocket soared close to a sundog just as the spacecraft reached Max-Q, and a ripple effect was created around the spacecraft. You can watch the launch below to see what happened:
You’ve probably never before seen an image like the one above. That’s because it is the first time something like this has ever been created, and it is only possible thanks to two fairly recent NASA missions, the Solar Dynamics Observatory and the Lunar Reconnaissance Orbiter. We’ve shared previously how two or three times a year, SDO goes through “eclipse season” where it observes the Moon traveling across the Sun, blocking its view.
Now, Scott Wiessinger and Ernie Wright from Goddard Space Flight Center’s Scientific Visualization Studio used SDO and LRO data to create a model of the Moon that exactly matches SDO’s perspective of a lunar transit from October 7, 2010. They had to precisely match up data from the correct time and viewpoint for the two separate spacecraft, and the end result is this breathtaking image of the Sun and the Moon.
“The results look pretty neat,” Wiessinger said via email, “and it’s a great example of everything working: SDO image header data, which contains the spacecraft’s position; our information about lunar libration, elevation maps of the lunar surface, etc. It all lines up very nicely.”
‘Nicely’ is an understatement. How about “freaking awesome!”
And of course, they didn’t just stop there.
Since the data from both spacecraft are at such high resolution, if you zoom in to the LRO image, features of the Moon’s topography are visible, such as mountains and craters. This annotated image shows what all is visible on the Moon. And then there’s the wonderful and completely unique view in the background of SDO’s data of the Sun.
So while the imagery is awesome, this exercise also means that both missions are able to accurately provide images of what’s happening at any given moment in time.
Since the Solar Dynamics Observatory opened its multi-spectral eyes in space about three years ago, we’ve posted numerous videos and images from the mission, showing incredible views of our dynamic Sun. Scott Wiessinger from Goddard Space Flight Center’s Space Visualization Studio has put together great timelapse compilation of images from the past three years, as well as a one composite still image to “try to encapsulate a timelapse into one static graphic,” he told us via email. “I blended 25 stills from over the last year, and it’s interesting to see the bright bands of active regions.” Scott said he was fascinated by seeing the views of the Sun over a long range of time.
Within the video, (below) there are some great Easter egg hunts – things to see like partial eclipses, flares, comet Lovejoy, and the transit of Venus.
How many can you find?
SDO’s Atmospheric Imaging Assembly (AIA) captures a shot of the sun every 12 seconds in 10 different wavelengths, but the images shown here are based on a wavelength of 171 Angstroms, which is in the extreme ultraviolet range. It shows solar material at around 600,000 Kelvin. In this wavelength it is easy to see the Sun’s 25-day rotation as well as how solar activity has increased over three years as the Sun’s solar cycle has ramped up towards the peak of activity in its 11-year cycle.
You’ll also notice that during the course of the video, the Sun subtly increases and decreases in apparent size. This is because the distance between the SDO spacecraft and the Sun varies over time. The image is, however, remarkably consistent and stable despite the fact that SDO orbits the Earth at 6,876 miles per hour and the Earth orbits the sun at 67,062 miles per hour.
The Solar Dynamics Observatory captured this view as the Sun let loose with its biggest solar flare of the year so far. It’s not a real big one — a mid-level flare classified as an M6.5 – but an associated coronal mass ejection is heading towards Earth and could spur some nice auroae by this weekend. Spaceweather.com predicts the expanding cloud (see animation below) will probably deliver a glancing blow to Earth’s magnetic field late on April 12th or more likely April 13th. The NOAA Space Prediction Center forecasts this event to cause moderate (G2) Geomagnetic Storm activity, and predicts geomagnetic activity to start in the mid to latter part (UTC) of April 13. They add that the source region is still potent and well-positioned for more geoeffective activity in the next few days.
Twice a year, the Solar Dynamics Observatory performs a 360-degree roll about the axis on which it points toward the Sun. This produces some unique views, but the rolls are necessary to help calibrate the instruments, particularly the Helioseismic and Magnetic Imager (HMI) instrument, which is making precise measurements of the solar limb to study the shape of the Sun. The rolls also help the science teams to know how accurately the images are aligned with solar north.
But take this rolling imagery, add some goofy music and hopefully it adds a smile to your day!
On February 19 and 20, 2013, scientists watched a giant sunspot form in under 48 hours. It has grown to over six Earth diameters. This image by astrophotographer Paul Andrew shows a detailed, close-up view of this sunspot group, named AR 1678, imaged with a hydrogen alpha filter.
NASA said the spot quickly evolved into what’s called a delta region, which has a magnetic field that harbors energy for strong solar flares. NOAA forecasters estimate a 45% chance of M-flares and a 15% chance of X-flares during the next day.
Below is an image from the Solar Dynamics Observatory of this region on the Sun:
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Three years ago today, (February 11, 2010) I was standing at Kennedy Space Center watching the launch of the Solar Dynamics Observatory. The launch was spectacular, and included a unique effect as the Atlas rocket flew close to a sundog just as the spacecraft reached Max-Q, creating a ripple effect around the spacecraft. And so, SDO started off with a bang and she’s been producing incredible data ever since. The folks at Goddard Spaceflight Center’s Scientific Visualiation Studio have put together a highlight reel for the third year of SDO operations. You’ll see morphing sunspots, fountains of solar plasma, sun-grazing comets and more. Throughout its mission, SDO has not only studied the Sun, but also opened up several new, unexpected doors to scientific inquiry. Enjoy this “greatest hits” video of SDO’s third year.