STEREO (Solar TErrestrial RElations Observatory) is a solar observation and space weather detection mission launched in October 2006 comprising two nearly identical spacecraft, one orbiting ahead of Earth (STEREO A), and one behind (STEREO B.) This enables stereoscopic imaging of the Sun and solar phenomena such as coronal mass ejections (CME’s or solar storms). These are violent eruptions of matter from the sun, a billion tons of material travelling at a million miles an hour, that can disrupt satellites and power grids and put astronauts on the International Space Station at risk. Images are returned to Earth from a range of cameras aboard the twin spacecraft which when analysed not only help us understand why solar storms happen but also enable the speed and direction of storms to be calculated providing an early warning system of Earth bound storms. That’s where Solar Stormwatch comes in. The mission has produced over 25 terabytes of data – more than 100,000 images – which are made into short videos for Stormwatchers to analyse.
But solar storms are not the only thing the cameras have captured. Dust, comets and planets make regular appearances in the videos. The STEREO spacecraft are now further away from the Earth than they are from the Sun but at the start of the mission the Earth and Moon were up close in the field of view. Because the cameras were designed to detect the tenuous and faint light scattered by the solar wind (100 million million times fainter than the Sun) the bright Earth-Moon system caused all sorts of odd reflections in the camera optics.
The Solar Stormwatch picture of the year is, in fact, a picture of an optical effect! The Earth is just out of view on the right. The intensely bright sunlight reflecting off the Earth produced internal reflections in the telescope attached to the STEREO B camera causing a bright flare with a “ghost” ring to appear on the image. Fondly known as the “White Doughnut” is has made an appearance in several Solar Stormwatch videos but Stormwatchers thought that this appearance was a particularly beautiful one.
[Many thank to The Solar Stormwatch Forum moderator Jules for putting this post together and organising the vote for the Image of the Year]
Happy Half-Birthday Solar Stormwatch….Part 2.
Solar Stormwatchers look for storms on short videos taken by the wide angled cameras on board the Stereo spacecraft. However, as well as solar storms the Heliospheric Imagers record anything else that wanders into view. Space is a busy place and the science team don’t know what’s common out there and what’s not or how the cameras are coping with their space environment. We are helping to provide the answers. These are just some of the weird and unexpected things we have found:
Most of the sungrazing comets we see in the STEREO images are likely to be from the Kreutz group whose orbits take them extremely close to the Sun at perihelion. They are named after Heinrich Kreutz, who first demonstrated that they were related and were in fact remnants of a larger comet that broke up centuries ago. The comets vary in size and some of the smaller ones, just a few meters across, don’t survive their trip around the Sun. All videos are dated which means we can go here to identify the comets we see.
We’ve also had some famous names turn up on camera. Click the images to see the videos.
This video has 10 comets!! Some are very hard to spot. Have a go! Clue – there are 6 in the Ahead camera and 4 in Behind.
If you gaze sunwards for long enough you will eventually see all the solar system planets as they orbit around the Sun. The Heliospheric Imagers have picked up several planets and brighter asteroids. Venus, Jupiter and Mercury, are bright and easy to spot. Mars and Saturn are a little trickier. They look a lot like stars but the way they move gives them away as all the planets appear to move relative to the starry background.
One planet is particularly easy to spot – Earth. Just after launch the Earth and Moon were up close in the Stereo cameras’ field of view. Because the cameras were designed to detect the tenuous and faint light scattered by the solar wind (100 million million times fainter than the Sun) the bright Earth-Moon system caused all sorts of odd reflections in the camera optics producing rings, flashes and all manner of fireworks. Click here and here to see what I mean.
|Earth and Moon
Thanks to fellow Mod Quialiss for producing the excellent guide to spotting planets including these labelled pictures.
As you might have guessed these are particles (interplanetary dust and bits of space junk) which strike the Stereo spacecraft. An unexpected discovery was the presence of much more dust out there than previously thought. When the data has been analysed the team will have a much better knowledge of the distribution of dust around the Sun. This is what a particle strike looks like:
40 minute exposures are required to image the faint solar storms so anything drifting through the camera’s field of view close to the spacecraft will appear as a bright streak.
Solar Stormwatch team member Chris Davis said:
“We think what we are seeing is sunlight scattered off bits of the spacecraft that are knocked off by dust impacts. They look so dramatic because of the sensitivity of the cameras and the proximity of the dust (like trying to take a photo when it’s snowing!)”
You might be forgiven for thinking that dust is just an inconvenience and can be ignored but space makes dust more of a problem as both the dust and the spacecraft are moving. The team have estimated that the impact of a dust particle on the spacecraft could be anything between 3 kilogrammes and 3 tonnes!
Photographing bright objects is always a problem. If you don’t get the exposure right the optics can’t cope and peculiar flares, reflections and ghosting result. As the Stereo’s Heliospheric Imagers are calibrated to take images of faint solar storms a planet or even a bright star plays mayhhem with the CCD and the results can be intriguing. Have a look at the collection of optical effects is on the forum.
And if star clusters and the Milky Way are your thing – we even have them in Solar Stormwatch.
||The Milky Way
What more could you possibly want from an on-line solar astronomy project?
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Next time: Part 3 – Art, chat and NASA inspired baking
Jules is a volunteer moderator for the Solar Stormwatch Forum.