IRIS Movie of the Day
At least once a week a movie of the Sun taken by NASA's Interface Region Imaging Spectrograph (IRIS) is posted by one of the scientists operating the instrument.
Archive | About IMOD | Facebook | YouTube | IRIS Home
18 May 2016
Mercury transits reveals orbits of IRIS and SDO
Credit: IRIS, LMSAL/NASA, Wei Liu and Bart De Pontieu
The IRIS spacecraft is in a sun-synchronous polar orbit: it flies at heights of about 640 km over the north (or south) pole every 97 minutes. The Solar Dynamics Observatory (SDO) is in a geosynchronous orbit "hovering" at a distance of about 36,000 km above roughly the same longitude on Earth while making excursions to the northern and southern hemisphere during its 24 hour orbital period. Both spacecraft observed Mercury as it transited the solar disk but because of the different vantage points of IRIS and SDO the spacecraft saw Mercury on a different spot on the Sun at any given time. This parallax effect is the same as when an object appears to "jump" when you switch between your left and right eye (by covering the other eye) except that here your left eye is about 36000 km from your right eye. The movie nicely illustrates this: the background image shows what SDO observed (golden color), while we have added a "fake" Mercury on the background image along the white line which shows the path of Mercury on the solar disk as seen by IRIS. The two Mercury's are in very different locations on the Sun! The inset shows a blend of IRIS and SDO: notice the jumps of the background when we switch between IRIS and SDO.