You may have heard of Comet ISON, a comet discovered last year that is currently approaching the Sun. It is expected to be visible in the SOHO-LASCO C2 and C3: from SOHO’s viewpoint the comet enters from the lower right early on November 27 and exits towards the top near the end of November 30 this year.
It will also be visible from the COR1 and COR2 instruments on board both STEREO spacecraft. The SOHO Hotshot webpage for Comet ISON has many more links to more details on the path of the comet as seen from SOHO and STEREO. At the moment it looks like this, as seen by the Hubble Space Telescope. It might be a spectacular sight from Earth. The appearance of comets from Earth is hard to predict because how it looks when it gets closer to the Sun depends on the details of its composition. We’ll have to wait and see!
We are currently experiencing some technical difficulties with our main Helioviewer server. While we work on fixing it, we have moved all helioviewer.org services over to our backup server. All normal helioviewer.org services should be operating nominally. Please contact us if you notice anything amiss with helioviewer.org. JHelioviewer services are currently not operational, but we hope to have these up and running as soon as possible. Near real-time AIA and HMI images should be available as usual; streams of images from SOHO, STEREO and PROBA2 should be back to near real-time within 24 hours.
We apologize for the interruption to Helioviewer services, and we thank you for your patience.
We are happy to announce the availability of full disk Yohkoh Soft X-ray Telescope (SXT) images on helioviewer.org. SXT images x-rays from the Sun, and therefore looked at some of the hottest plasmas on the Sun. These data are important in trying to understand solar flares and the heating of the Sun’s corona.
Yohkoh (“Sunshine”) was launched in August 30, 1991, from the Kagoshima Space Center (Uchinoura) in Japan, and was a project of the Japanese Institute of Space and Astronautical Science (ISAS). The scientific objective was to observe the energetic phenomena taking place on the Sun, specifically solar flares in x-ray and gamma-ray emissions.
Yohkoh carried four instruments to detect energetic emissions from the Sun: the Soft X-Ray Telescope (SXT), the Hard X-Ray Telescope (HXT), the Bragg Crystal Spectrometer (BCS) and the Wide Band Spectrometer (WBS). A team from the United States collaborated on SXT, and teams from the United States and the United Kingdom collaborated on BCS.
SXT imaged X-rays in the 0.25 – 4.0 keV range. SXT used thin metallic filters to acquire images in restricted portions of the energy range. We are making images from the thin aluminium filter (thin-Al), and the aluminium-magnesium-manganese filter (AlMgMn) available. White-light images are also available up until November 1992. An example thin-aluminium image is shown below.
SXT could resolve features down to 2.5 arc seconds in size. Information about the temperature and density of the plasma emitting the observed x-rays was obtained by comparing images acquired with the different filters. Flare images could be obtained every 2 seconds. Smaller images with a single filter could be obtained as frequently as once every 0.5 seconds.
Yohkoh ceased operations on December 14, 2001. The SXT images we are making available cover portions of Solar Cycles 22 and 23 (we are currently somewhere close to the maximum of Solar Cyce 24). This historical data allows us to compare current solar behavior to previous solar behavior. Such studies allow us to better understand how the Sun operates on timescales of decades and longer.
Yohkoh SXT images are the first images of soft X-ray data available on helioviewer.org. We hope you enjoy examining this different view of the Sun on helioviewer.org.
Maintenance operations on the Helioviewer server are now complete, ahead of schedule. All Helioviewer services should be up and running as normal. We thank you for your patience in the last three days while our maintenance operations were ongoing. Please contact us if you notice a departure from normal services.
Today’s announced maintenance has been postponed until Friday 1st February. Helioviewer services will be brought down around 1600-1700 UT and will be brought back up no later than 2200 UT. We apologize for any inconvenience this may cause.
All Helioviewer services (helioviewer.org, JHelioviewer and the embed functionality) will be temporarily suspended today (30 January 2013) to allow for maintenance of our server. We anticipate that services will be suspended at around or before 1700 UT and will resume again at around 2230 UT at the latest (could be much earlier). We apologize for any inconvenience this may cause.
From today’s SDO blog entry:
Today, starting at 1315 UTC (8:15 am ET), SDO will execute the EVE Field of View maneuver followed by the HMI/AIA Flatfield at 1630 UTC (11:30 am ET). During these maneuvers the science data will be interrupted. These maneuvers and last weeks’ Delta-H thruster firing were flipped in the schedule published earlier.
Instruments can degrade in the harsh environment of space, and so it is important to calibrate at regular intervals to make sure that we have the best data available at all times. SDO therefore occasionally makes special maneuvers that enable the measurements to be made that can be used to help calibrate the instruments onboard. Whilst these maneuvers are going on, some of the AIA and SDO images may look unusual.
SDO has three instruments onboard: AIA, HMI and the Extreme Ultraviolet Experiment, EVE. The EVE instrument is designed to measure the solar extreme ultraviolet (EUV) irradiance. The EUV radiation includes the 0.1-105 nm range, which provides the majority of the energy for heating Earth’s thermosphere and creating Earth’s ionosphere (charged plasma). The majority of EVE data are time-series of measurements of the spectral content of solar extreme ultraviolet irradiance, although some low spatial resolution x-ray images are also taken by the EVE Solar Aspect Monitor (SAM) instrument (see the example below). EVE gives us lots of information on the spectral content of the Sun’s radiation changes with time, which is very important for understanding the Earth-Sun connection.
As the movie progresses, you see a small eruption take place. As the eruption starts, you can clearly see the southern base of the loop displace. The loop appears to be released in some way, which shakes the whole loop along its entire length. This event is a great example of a transverse coronal loop oscillation. These were first observed by the Transition Region and Coronal Explorer (TRACE) in 1998. Since these initial observations, many more examples have been observed, by both TRACE and AIA. The mechanism of the excitation of these waves remains hidden, but it can be connected with a blast wave generated in a flare epicentre. For scale, the Earth is roughly the same size as the Helioviewer logo in the bottom right hand corner of the movie.
although it is much more difficult to see in the AIA 193 Angstrom channel compared to the AIA 171 Angstrom channedl(the dark wavy material you see are motions in a prominence, not the same as the coronal loop oscillation).
Observations of coronal loop oscillations, coupled with a theoretical understanding of how these oscillations behave in the coronal plasma has lead to a new field of study called coronal seismology. Coronal seismology is analogous to seismology on Earth. Seismology is the study of earthquakes and the propagation of waves arising from earthquakes, and can be used to infer properties of the structure of the Earth. Similarly, coronal seismology is used to measure properties of the Sun’s coronal plasma. Using coronal seismology, we can derive the density and magnetic field of the coronal plasma, measurements that are difficult make in other ways.
A total solar eclipse will be visible in the Southern Hemisphere on November 13.
Eclipse first contact begins at approximately 20:36 UT on November 13 and continues until approximately 23:48 UT on November 13. Live streaming of the eclipse is available at http://www.ustream.tv/cairnseclipse2012. Please go to
for many more details concerning this eclipse. An interactive map is available here.
Hurricane Sandy is currently approaching the East Coast of the United States. Winds from the hurricane are expected to cause widespread power outages in the next 48 hours (Oct 29-30). Since an unplanned power outage to a server can cause severe damage, we are taking the precautionary measure of shutting down the Helioviewer server. The server will shut down in the next hour. We expect to be back online by Wednesday 31st October EST at the latest, contingent on the weather and the availability of power. We apologize for the inconvenience this will cause.