Lunar Transit Last Night!

Yesterday, from 6:00--8:33 pm, the Moon moved between SDO and the Sun. These lunar transits happen a few times each year. Here is the FOT movie of the event, produced last year. The transit covered a maximum of 57% of the Sun.

And here is a 60-hour movie in AIA 171 Å. There are three eclipses of the Sun by the Earth near 0700 UTC on February 22, 23, and 24. The lunar transit starts at 2300 UTC on February 23 and lasts until 0133 UTC on the 24th.

Lunar transits are one interesting feature of life in a geosynchronous orbit.

Station Keeping Maneuver #20 Today

SDO will execute Station Keeping Maneuver #20 today at 2230 UTC (5:30 p.m. ET). From 2200 to 2250 UTC (5:00-5:50 p.m. ET) science data may be missing or blurred. Station-keeping maneuvers are designed to keep SDO’s orbit in the right place when the spacecraft travels through the geostationary belt twice each day.

Happy Anniversary SDO!

Ten years ago, 11 Feb 2010, SDO rose majestically into the Florida skies. Since that day we have taken and recorded over 350 million images of the Sun.

Here's the image closest to the launch time, a lovely 211 Å image showing a large coronal hole over the South Pole and a smaller one over the north. Pretty typical solar minimum portrait!

Over the next year, Solar Cycle 25 will become more and more apparent. SDO will be there, observing the Sun and its magnetic field.

Congratulations to the SDO teams and all the people who enjoy our data!

Calibration Maneuvers Today

Today from 1315-1915 UTC (8:15 am - 2:15 pm ET) SDO will perform the EVE Field of View and HMI/AIA Flatfield calibration maneuvers. Science data recorded during these maneuvers may be missing, incomplete, or blurry.

Happy Perihelion!

On January 5, 2020, at 0547 UTC (2:47 am ET) the Earth reached perihelion in its orbit around the Sun. At that time the Earth was 147,091,144 km (91,381,199 mi) from the Sun. The Earth's will reach aphelion, the point in our elliptical orbit furthest from the Sun, on June 4, 2020. Enjoy the closest of our favorite star, the Sun!

200 Millionth Image from AIA

In all the hype about the Mercury transit last Monday, we overlooked another milestone in the SDO mission. On November 5, 2019, the AIA instrument returned its 200 millionth image. Here it is and it's a beauty in the AIA 171 Å passband!

The Sun looks like it is in solar minimum, with large polar coronal holes over the North and South poles. Hope for the future can be seen in the area with the black line drawn around it. That's active region 12750, a small bi-polar region that has the polarity of Solar Cycle 25 and an appropriately high latitude of 28°S. Other SC25 regions have been seen and they will become more frequent as SC25 starts its rise to maximum.

Mark Cheung, PI of AIA, made a movie to celebrate this milestone.

Congratulations to the AIA team for building a robust instrument that has returned excellent data for almost 10 years.

Extraordinary Pictures of the 2019 Mercury Transit

Here are composite views of Monday's transit (top) and the transit in 2016 (bottom). They were produced by Monica Bobra at Stanford University. What can we learn about Mercury's orbit from these pictures?

November 11, 2019, Courtesy of Monica Bobra

First, the images of Mercury (the black dots) are 21 minutes apart in both images. The 2019 dots are further apart than the 2016 dots. This means Mercury was moving faster across the Sun in 2019. If we check the orbit of Mercury at AstroPixels, we find that Mercury was closest to the Sun (at perihelion) on November 16, 2019. A planet's velocity is greatest near perihelion and least near aphelion (the furthest point from the Sun). So Mercury was moving at almost its maximum speed on Monday. The 2016 Mercury ephemeris shows that aphelion was May 20, 2016, only 11 days after the transit that year. That means Mercury was moving at almost its slowest speed during the 2016 transit. The spacing of the dots agrees with the orbit of Mercury.

May 9, 2016, Courtesy of Monica Bobra

We can also look at the size of Mercury on the disk. The dots are smaller in 2019, showing that Mercury was further from the Earth during this transit. If we look at Mercury's elliptical orbit from the Earth, Mercury is closest to the Earth when it is furthest from the Sun (aphelion) and farthest from the Earth when it is closest to the Sun (perihelion). Again, this agrees with the transit pictures and orbit.

The different tilts of the two paths show that Mercury's orbit is tilted away from the Earth's orbit (called the ecliptic) and the Sun's equator. Whenever Mercury's orbit crosses the ecliptic we have a chance to see a transit, but most crossings take place when the Earth and Mercury are not aligned. SDO images are usually aligned with the Sun's North Pole at the top of the image. So the interpretation of the tilts in a little more complicated.

We can see sunspots in the 2016 images but not in the 2019 image. The Sun has become very quiet in the last three years. Over the next year or so we should start seeing Solar Cycle 25 activity. But on Monday the Sun was blank in visible light, providing beautiful back-lighting for us to see Mercury.

The sunspots in the 2016 image are nice and sharp. Bobra's program does not use a simple average to make the image. You can check out the actual Python code (with the transit pictures) at her Planetary Transit githib site. Be ready for the 2032 transit!

Check out the 2019 transit in other wavelengths of light at the SDO website.

Many thanks to Dr. Bobra for producing these extraordinary images.