Earth Photobombs Space Observatory's Pristine Solar View
It's eclipse season for NASA's Solar Dynamics Observatory (SDO), a time when our own planet can't bear to to be out of the spotlight and barges its way into the shot.
It's "eclipse season" for NASA's Solar Dynamics Observatory (SDO), a time when our planet can't bear to to be out of the spotlight and barges its way into the shot.
The SDO was launched in 2009 and placed in a near-circular, 22,238 mile geosynchronous orbit around Earth. For the vast majority of its observing time of our nearest star, the SDO has an unblocked, pristine view, returning the highest-definition observations of solar phenomena such as solar flares, coronal mass ejections (CMEs), coronal loops, prominences and sunspots. Occasionally, however, the Earth inevitably lines up just right during its solar orbit that it creeps into the SDO's frame and interrupts the photo session.
We are currently in the middle of the 2016 spring eclipse season that will last until March 12. It began on Feb. 19. Every year there are 2 eclipse seasons, both near the equinoxes - a bi-annual event when the sun is positioned directly over the Earth's equator and the Northern and Southern Hemispheres receive the same amount of sunlight.
As can be expected around the start and end of the SDO eclipse season, the amount of solar blockage is limited, but in the middle of the eclipse season (around now), the eclipse can last up to 72 minutes.
Any spacecraft orbiting the Earth that observes the sun contend with these eclipses, but the SDO is in an orbit designed to minimize the interruption.
This animation is constructed of ultraviolet observations made by the SDO at a wavelength of 304 Angstroms. At this wavelength, features in the sun's lower corona (the sun's multimillion degree atmosphere) can be resolved. The brightest patches are where highly energetic plasma heating processes are underway, producing so-called active regions.
As the Earth passes in front, these regions can be seen through the fuzzy edge of the Earth as the UV light penetrates through our atmosphere.
The sun may be an average star when compared to the menagerie of stars that exist in our galaxy, but to Earth and all life on our planet, the sun is the most important object in the Universe. However, regardless of its importance and close proximity, our nearest star holds many mysteries that continue to fox solar physicists after decades of modern studies with cutting-edge observatories. One of the biggest mysteries surrounding the sun is the underlying mechanisms that drive solar flares and coronal mass ejections (CMEs). Monday evening (EST), the sun reminded us that it hasn't quite finished with the current solar maximum (of solar cycle 24), unleashing a powerful X4.9 solar flare -- the biggest of 2014. An armada of space telescopes witnessed the event, including NASA's Solar Dynamics Observatory that can spy the sun's temper tantrums in astounding high definition. Shown here, 5 of the 10 filters from the SDO's Atmospheric Imaging Assembly (AIA) instrument are featured, showing the sun's lower corona (the solar multimillion degree atmosphere) through 5 wavelengths; each wavelength of extreme ultraviolet light representing a different plasma temperature and key coronal features -- such as coronal loops (highlighted here in the 'yellow' 171A filter) and ejected plasma that formed a CME.
At 7:13 p.m. EST (00:13 UT, Feb. 25) -- pictured here on the far left -- the active region (AR) 1990 was crackling with activity. Then, as magnetic field lines from the sun's interior forced together and through the solar photosphere, large-scale reconnection events occurred. Reconnection is a magnetic phenomena where field lines "snap" and reconnect, releasing huge quantities of energy in the process. At 7:44 p.m. EST (00:44 UT) -- second frame from the right -- a kinked coronal loop can be seen rising into the corona. At 7:59 p.m. EST (00:59 UT) -- far right -- solar plasma contained within the magnetic flux is accelerated to high energy, generating powerful x-rays and extreme ultraviolet radiation, creating the X-class flare.
The X4.9 flare was caught through the range of SDO fliters, including this dramatic view as seen through the 131A filter. The flare was so bright that photons from the flare overloaded the SDO's CCD inside the AIA instrument, causing the signal to "bleed" across the pixels. This bleeding effect is common for any optical instrument observing powerful solar flares.
Intense coronal activity is often associated with active regions -- the active lower corona is pictured here, left. In this case, the flare erupted from AR1990, at the limb of the sun. Also associated with active regions are sunspots, dark patches observed in the sun's photosphere (colloquially known as the sun's "surface") -- pictured right. The sun's cooler photosphere has been imaged by a different SDO instrument called Helioseismic and Magnetic Imager (HMI), which detects the intensity of magnetic fields threading though the sun's lower corona and photosphere.
In the case of AR1990, a large sunspot can be seen at the base of the coronal loops that erupted to generate the powerful flare. This is a prime example of how sunspots can be used to gauge solar activity and how they are often found at the base of intense coronal activity and flares.
The HMI monitors magnetic activity across the disk of the sun and can also generate a picture on the direction of the magnetic field polarity. In this observation of the sun's magnetic field around the time of the recent X-class flare, other active regions can be easily seen -- intense white and black regions highlighting where magnetic field lines emerge and sink back into the sun's interior in active regions.
The joint NASA/ESA Solar and Heliospheric Observatory (SOHO), which has been watching the sun since 1996, also spotted the flare, tracking a CME that was generated shortly after. Seen here by SOHO's LASCO C2 instrument, that monitors the interplanetary environment surrounding the sun for CMEs and comets, a growing bubble of solar plasma races away from the sun.
Approximately an hour after the flare, the CME grew and continued to barrel into interplanetary space. Space weather forecasters don't expect that this CME will interact with the Earth's atmosphere as it is not Earth-directed. This observation was captured by SOHO's LASCO C3 instrument -- an occulting disk covers the sun to block out any glaring effect. By combining observations by the SDO, SOHO and other solar observatories, the connection between the sun's internal magnetic "dynamo", the solar cycle, flares and CMEs, solar physicists are slowly piecing together what makes our nearest star tick, hopefully solving some of the most persistent mysteries along the way.