Is NASA Hiding Something? No, But The Earth Is

Pictures of the sun snapped every 15 minutes by the orbiting Solar Dynamics Observatory. Data appears to be missing from the middle five frames. Credit: NASA

So what’s up with those blank squares? You’re looking at a screen capture of a page of pictures of the sun in photographed in ultraviolet light by NASA’s Solar Dynamics Observatory (SDO). The photos were shot 15 minutes apart starting Wednesday evening into Thursday morning this week.

Since SDO circles Earth in a geosynchronous orbit about 22,000 miles high, it “sees” the sun continuously both day and night from a vantage point high above Mexico and the Pacific Ocean. About 1.5 terabytes of solar data or the equivalent of half a million songs from iTunes are downloaded to antennas in White Sands, New Mexico every day. The space station, which orbits much closer to Earth, would make a poor solar observatory since Earth blocks the sun for half of every 90 minute orbit.

SDO’s eclipse season started around 1 a.m. September 6 when the observatory shot a photo of the Earth (top middle) cutting across the sun. Credit: NASA

Did I say SDO watches the sun continuously? Well, not quite. Twice a year for a period of about three weeks around the equinoxes, the Earth gets in the way of the sun from the space craft’s point of view, causing a total solar eclipse. The latest round of eclipses began on September 6 and will conclude on the 26th.

Now you know the reason for the blank frames – it’s a conspiracy by the Earth to block out the sun. The blackness is none other than the planet itself.

Normally the Earth is out of the way of the sun from SDO’s perspective but twice a year its orbit and Earth’s orientation to the sun cause Earth eclipses. Credit: NASA

Total eclipse happens every day between 1 and 2 a.m. local time (Mountain Daylight Time) when the Earth blocks the sun from SDO’s view. In similar fashion, we experience a solar eclipse on the ground when the moon covers up the sun. You can watch for pictures of the partial eclipse as Earth gets out of the way sometime next Tuesday the 25th by going to the SDO website. Follow these simple steps to find and view the images:

* Click on the Data tab and select AIA/HMI Browse Data
* Click on the Enter Start Date window, select a start date and click Done
* Click on Enter End Date and click Done
* Under Telescopes, pick the color (wavelength) sun you want
* Select Images in the display box
* Click Submit at the bottom and then browse the pictures

Not only does the Earth cross the sun from the observatory’s perspective, so does the moon (left) on occasion. The moon’s”bite” smaller and sharper. Earth’s atmosphere gives our planet a soft, diffuse edge compared to the airless moon’s. Photo at right was taken on September 6, 2012 at eclipse season start. Credit: NASA

While watching an eclipse of the sun by the Earth is one of the joys of living in the space age, there are other cool things to see from SDO’s perspective. Look at the drastic difference between the moon’s sharp outline and Earth’s fuzzy edge. Our planet “bites softly” into the sun because its substantial atmosphere grades from thick to thin, filtering the sunlight that passes through it. The moon’s a big baldy. With no air to grade and soften the light, the sun shines crisply right up to its edge.

Video of a partial eclipse of the sun by Earth. Refraction of light by Earth’s atmosphere causes the sun to bend at its edges. Credit: NASA SDO / Stanford University for HMI

We’ve seen how air can also bend or refract sunlight in strange ways, going so far as to “lift” the sun  into view when it’s still below the horizon.  You can see the same effect in a brand new way in this short video of an SDO partial eclipse. Watch the sun’s edge bend as the Earth rolls by. Compare it to a similar eclipse by the moon below.

Moon eclipsing sun via SDO 

SDO orbits about 22,000 miles above Earth, tracing out a figure-8 (called an analemma) above the Pacific and Mexico every 24 hours. Credit: NASA

SDO amazes with its spectacular pictures of the sun taken in 10 different wavelengths of light every 10 seconds; additional instruments study vibrations on the sun’s surface, magnetic fields and how much UV radiation the sun pours into space.

It’s the latest, greatest “Swiss Army knife” used by scientists to pry open the inner workings of the sun. The eclipses, while a gap in the data stream,  are a sweet bonus all their own.

4 Responses

  1. Jonny

    Hey BoB,
    1st let me say that I enjoy the blog it keeps me well informed. Now with this missing data can NASA still keep track with solar storms ( space weather)? Also has there been any extreme solar activity lately becuase at one point and time I remember seeing a lot of aurora in past couple of months.

    1. astrobob

      Hi Jonny,
      Glad you like the blog. Yes, NASA has several other spacecraft watching the sun including STEREO A and B, which allow us to see the front and back of the sun at the same time. As for solar activity, yes, we’ve had some good flares this year with a few fine auroras. Lately though it’s been on the quiet side again.

  2. Edward M. BOll

    Laurel and Hardy are 2 of my favorites too. My wife and I are planning on being in Duluth Oct. 9 and 10. I hope that the sky is clear Tuesday morning to see the close Venus Regulus conjunction.

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