When the Earth photobombs the Sun

By Phil Plait | March 13, 2012 12:43 pm

The Solar Dynamics Observatory is a NASA satellite that observes the Sun 24 hours a day. It orbits the Earth, placed carefully so that it takes 24 hours to circle the Earth once — what we call a geosynchronous orbit. This maximizes its output, and allows scientists to squeeze as much data from it as possible.

But, twice a year, the geometry of SDO’s orbit aligns in such a way that the Earth itself gets between the observatory and the Sun. When that happens, you get an eclipse! We’re in one of those "eclipse seasons" now, and around midnight last night UTC one such eclipse occurred. The folks at SDO created a nifty video from the images collected during that time:

That’s cool. You can see the Earth barreling through the image, blocking SDO’s view. SDO has several different cameras which look at the Sun at different wavelengths of ultraviolet and optical light. The first view, colored red, is actually in ultraviolet (at 304 Angstroms, if you’re keeping track). The next view, colored gold, is even further in the UV (193 Angstroms). Then they cycle through a bunch of different wavelengths, giving a psychedelic journey through an eclipse that reminds me of the ferry ride from "Willy Wonka".

"There’s no earthly way of knowing, which direction we are going…"

I’ve written about all this before; see Related Posts below for more.

And I’ll leave you with this question: when the Moon passes between the Earth and the Sun, it’s a solar eclipse, and when the Earth passes between the Sun and the Moon, it’s a lunar eclipse. So what do we call it when, for us on the surface, the Earth gets in between us and the Sun?

Answer: night.

Tip o’ the dew shield to Camilla Corona SDO on Google+.

Related Posts:

When the Earth takes a bite out of the Sun
Moon bites multicolor Sun… from space!
An eclipse from space with a two-way Moon
SDO lunar transit: now with video!
Solar eclipse, from space!

CATEGORIZED UNDER: Astronomy, Cool stuff
MORE ABOUT: Earth, eclipse, SDO

Comments (27)

  1. paulmc

    Shouldn’t that be nanometers for the wavelength of UV light?

  2. Pepijn

    Very cool!

    What is the large triangular dark patch which you can see on the Sun in some of the wavelengths? Is that an artefact from the way the image is taken (and if so how is it caused?), or is it really present on the Sun?

  3. Duh. “Night.” Duh.

    Cool film, though.

  4. stuart

    What is it called when the earth gets between us and the sun? Sunset!

  5. Night is correct, but now I want to call “night” “Terran eclipse”. Just because.

  6. Steeev

    A “Terrestrial Eclipse” would be when the Sun passes between the Earth and the Moon.

    Fortunately, these are pretty rare.

  7. HP

    Well, there’s the classic Arthur C. Clarke story called “Transit of Earth.”

  8. Musical Lottie

    @Steeev #6 – LOL!

    I also rather like ‘Terran eclipse’ for night 😀

  9. Rick White in TX

    The dark area on the sun looks like the Lombardi Trophy.

  10. Hmmm, Terran eclipse sounds good. So, I’d either go with that or go with orbital eclipse.

  11. OtherRob

    Yeah, what is that triangle?

  12. The triangle isn’t an image artifact, it’s real.

    It’s apparently called a “coronal hole,” and it’s a gap in the magnetic field of the sun. Escaping coronal material causes the area to cool down relative to the rest of the image, which makes it appear darker at certain wavelengths.

    Click my name for a Universe Today article explaining the phenomenon, with neat pictures.

  13. Blargh

    @ paulmc
    Actually no. Both are in the “extreme ultraviolet” range at 30.4 and 19.3 nm, respectively (the Ångström is a rather silly unit to use when there’s SI). Wikipedia has a pretty good summary of the SDO’s instruments.

    @ The Librarian With No Name
    Thanks a lot!

  14. Dan I

    @6 Steeve

    Yeah they only happen once a day 😛

  15. That triangular “hole” is clearly a Gigantor-class Imperial Star Destroyer passing in front of the Sun!

  16. Dave

    Can I ask a question that betrays my ignorance?
    I’m having difficulty in understanding how a satellite in geosynchronous orbit can observe the sun for 24 continuously? Won’t the Earth get in the way once in 24 hours?

    Unless the satellite is so far away that the Earth gets in the way only twice a year? Is that the answer?

  17. John

    Very cool video… I especially liked the reference to Gene Wilder, who was brilliant in that role. There were some great lines in that movie — “Violet, you’re turning violet, Violet!” “Candy is dandy but liquor is quicker.”

  18. Blargh

    Dave: geosynchronous doesn’t necessarily mean geostationary!

    A geosynchronous orbit has an orbital period of exactly one (sidereal) day. A geostationary orbit is a geosynchronous orbit in the plane of the equator. The latter will appear to hover over the same spot on the Earth while the former will simply return to the same spot over the Earth at the same time every (sidereal) day. The latter will necessarily be in the Earth’s shadow once every day, the former doesn’t (it helps if you have a globe handy to visualize it!).

    SDO’s orbit is geosynchronous but not geostationary – its orbit is inclined 28° from the equatorial plane.

    (Either way, a circular geosynchronous orbit means a distance from the Earth of more than 40000 km – a long way off – which helps to avoid the Earth’s shadow)

  19. Monkey
  20. There’s no earthly way of knowing, which direction we are going…” Three mutually orthogonal fiberoptic laser ring gyros ought to satisfy any doubts. We desperately require emergency national legislation to prohibit, pursue, prosecute, and punish spectral discrimination. Within our lifetime we can render all transitions grey, impose a hegemony of beige upon all optical elements, and put an end to diffraction.

    Then… we address de Broglie waves and hunt down electron microscopes, ion milling; and Colella-Overhauser-Werner, Bonse-Wroblewski, and Kasevich-Chu interferometers. Render the Earth pure and holy!

  21. OtherRob

    Thanks for the info about the coronal hole.

  22. Mike Torr

    OK, so we know what the triangle is now. What about the tethered plasma sphere that has been spotted and is giving the UFO sites something to report on at the moment? Has anyone seen that?

  23. Dave

    @Blargh – you’re right, I need to get a globe. My head is hurting from trying to visualize it :)
    Thanks for the answer!

  24. Mark

    #6. @ Steeev

    How in the Universe could the Sun be between the Earth and the Moon? The Sun will never be between the Earth and the Moon. That is NOT POSSIBLE to happen.


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