This is the Solar Dynamics Observatory Mission blog. It will consist of mission status, news, and event updates.
The Moon moves from left to right during this transit. That makes it an SDO-overtake transit.
Although you can see the Moon throughout the movie SDO's instruments cannot see the Moon when it is not covering the Sun. The little white flash seen in the Moon is the word "Moon" being written by the software and then quickly covered. The boxes drawn around and on the Sun help the FOT run the spacecraft. The time is displayed in the lower left corner of the movie. The first seven numbers are the year (2018) and the day of year (311). The six numbers after the period are the hour, minutes, and second of UTC (2 numbers each).
The next SDO lLunar Transit will be on March 6, 2019. That one will also be a double transit similar to the one in September 2018.
For example, the coatings on the HMI instrument housings and optical surfaces have been degrading slowly but steadily, causing the instrument to absorb more solar radiation and heat up. The front surface of HMI’s telescope is now hot enough that the HMI team is having difficulty maintaining proper focus. Without some adjustments, this problem will only get worse as the instrument continues to age.
For this reason, the HMI team is going to increase the operating temperatures of the front of the telescope and adjust the internal focus mechanism. This should give the instrument many more years of precise control and excellent data. The process of increasing the operating temperatures is a slow one — the team will begin heating the front telescope tube up at 1000 UTC on Tuesday, October 16, and will then wait six hours for the temperature to stabilize. The next step is to fine-tune the temperatures. These smaller changes will need about an hour for the temperature to become constant. Science data will not be available during the time it takes to bring the instrument back into focus. That also means there will be no magnetic field, continuum, or Doppler NRT data products.
HMI resumed taking science data before 2130 UTC, October 16. Fine tuning of the focus will occur Wednesday, October 17, but science data will not be interrupted.
The Moon moves from left to right during the first transit and right to left for the second. The first transit is caused by SDO overtaking the Moon as SDO moves in the afternoon part of its orbit. (SDO orbits over the Mountain Time Zone of the USA.) SDO's velocity of about 3 km/s is faster than the Moon's of 1 km/s and SDO overtakes and moves past the Moon-Sun line. The second transit happens after SDO has moved into the evening part of the orbit and is now moving mostly away from the Moon in SDO's orbit around the Earth. The Moon's velocity takes it past the Sun and the shadow appears to move from right to left.
During the total solar eclipse last year the Moon's shadow moved from the West coast of the US towards the East. This is because the speed of the rotation of the Earth (less than 0.5 km/s) is slower than the speed of the Moon. That means the motion of the Moon overtakes the motion of the Earth. The shadow follows the Moon and moves from West to East, like the second transit.
Although you can see the Moon throughout the movie SDO's instruments cannot see the Moon when it is not covering the Sun. The little white flash seen in the Moon is the word "Moon" being written by the software and then quickly covered. The boxes drawn around and on the Sun help the FOT run the spacecraft. The time is displayed in the lower left corner of the movie. The first seven numbers are the year (2018) and the day of year (252 and 253). The six numbers after the period are the hour, minutes, and second of UTC (2 numbers each).
When I first saw this movie I thought we were going to talk about retrograde motion. Other planets, especially Mars, move in retrograde as the Earth moves past them with our faster orbital velocity. But it isn't just that. The first transit is like retrograde motion as SDO passes by the Moon-Sun line with its faster velocity and the Moon appears to move backwards. But the second transit happens because SDO is moving mostly away from and a little in the opposite direction of the Moon.
This double transit shows how complicated the motions of objects can appear even as they move along simple orbits.
During the maneuver science data may be missing or blurry.
If this had been a real comet observation the scientists would want to examine the missing right-hand side for the comet tail. AIA 171 Å was our best channel for looking at the comets.
My thanks to the SDO Flight Operations Team for making the test look easy.
The Sun will appear to shift to the left during the test. That means it is useful for Kreutz comets in July and August, when the comets appear to come from the right and pass across the face of the Sun. Some science data, such as magnetograms and Dopplergrams, will not be produced while the Sun is shifted from the center of the images.
When a sun-grazing comet arrives, we will be ready to go comet watching!
Here are other planned maneuvers through the rest of 2018.
The pair of Lunar Transits on September 9th and 10th are separated by approximately 4 hours 22 minutes, so they are considered separate events. However, the relative motion of SDO and the Moon cause what could be a single transit to split into two. We will discuss this more as we approach the transits.
The sun and moon will be separated by 0.604° on August 21, 2018. (The Sun is 0.5° across, so the Moon is not in the field of view of the SDO images.) This is not close enough to be flagged as a transit, but the proximity may be of interest.