We will point SDO at three different positions as Comet ISON moves through perihelion on November 28, 2013. This will let us look for the tail of the comet in our images. This movie shows you how we will point SDO. The clock in the lower left corner shows approximate UTC as a decimal.
This website will allow you to see the images taken while we are looking for the comet. The "kiosk" option will flip through the images as they arrive and let you look for the comet. Select a phase (approach, perihelion, or departure) and one of the four wavelengths and a new window will open with the images available for that wavelength. The Sun will be a different position in the window for each phase. The comet should move through the middle of the window. The comet will probably be very faint!
Images from SDO take about 6 minutes to move from the spacecraft to our computer at Goddard. We plan to off-point at 17:30 UTC (12:30 pm ET) and return to normal solar observing at 20:45 UTC (3:45 pm ET). We will begin posting images after SDO completes the first repointing maneuver and we obtain and process the data. Images should begin appearing sometime between 12:45 pm and 1:00 pm ET.
This site also includes mp4 movies of the comet in each phase and wavelength. These movies will be rebuilt every 5 minutes during each phase and must be reloaded to update the images.
Lastly, Dopplergrams and magnetograms will not be available while SDO is pointed away from the Sun.
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) may be designed to provide an unprecedented view of the solar corona, but it sees comets in a different light.
When we see a comet in AIA we see light coming from ions of oxygen. Comets have a lot of oxygen (water ice is one part oxygen to two parts hydrogen) and that oxygen can light up the corona for quite awhile after it sublimates off the comet. The brightness fades as the oxygen spreads out into the corona and eventually the normal glow of iron ions returns.
This channel is especially good at showing coronal loops - the arcs extending off of the Sun where plasma moves along magnetic field lines. The brightest spots seen here are locations where the magnetic field near the surface is exceptionally strong.
Where: Quiet corona and upper transition region
Wavelength: 171 angstroms (0.0000000171 m) = Extreme Ultraviolet
Primary ions seen: 8 times ionized iron (Fe IX)
Characteristic temperature: 1 million K (1.8 million F)
This channel highlights the outer atmosphere of the Sun - called the corona - as well as hot flare plasma. Hot active regions, solar flares, and coronal mass ejections will appear bright here. The dark areas - called coronal holes - are places where very little radiation is emitted, yet are the main source of solar wind particles.
Where: Corona and hot flare plasma
Wavelength: 193 angstroms (0.0000000193 m) = Extreme Ultraviolet
Primary ions seen: 11 times ionized iron (Fe XII)
Characteristic temperature: 1.25 million K (2.25 million F)
This channel (as well as AIA 335) highlights the active region of the outer atmosphere of the Sun - the corona. Active regions, solar flares, and coronal mass ejections will appear bright here. The dark areas - called coronal holes - are places where very little radiation is emitted, yet are the main source of solar wind particles.
Where: Active regions of the corona
Wavelength: 211 angstroms (0.0000000211 m) = Extreme Ultraviolet
Primary ions seen: 13 times ionized iron (Fe XIV)
Characteristic temperature: 2 million K (3.6 million F)
This channel is designed to study solar flares. It measures extremely hot temperatures around 10 million K (18 million F), as well as cool plasmas around 400,000 K (720,000 F). It can take images every 2 seconds (instead of 10) in a reduced field of view in order to look at flares in more detail.
Where: Flaring regions of the corona
Wavelength: 131 angstroms (0.0000000131 m) = Extreme Ultraviolet
Primary ions seen: 20 and 7 times ionized iron (Fe VIII, Fe XXI)
Characteristic temperatures: 10 million K (18 million F)
A comet's orbit can be very difficult to image. They move in all three dimensions along their orbit. Here is a way to see the orbits of the sungrazing Comets ISON and Lovejoy as they fly by the Sun. The paths of the comets are drawn with a bluish color up to perihelion and another after perihelion. You can use your mouse to grab and rotate the orbits. Look at them from many points of view. See how an orbit can appear to be very close to the Sun even if it is not. The straight black line points to the position of the Earth on November 28, 2013. That allows you to get oriented to what we will look at on Thanksgiving Day.