STEREO scoping

By Phil Plait | February 7, 2011 12:01 pm

On Sunday I posted about NASA’s twin STEREO spacecraft, which are now 90° ahead and behind the Earth in its orbit. From their vantage point, over 200 million kilometers away, they can together see the entire far side of the Sun and beam the images back to Earth, providing us with real time data impossible to get from home.

While I was going through old blog posts to look at entries I had written about STEREO, I found one showing some STEREO data that I thought was worth showing everyone again. Putting it in Sunday’s article would’ve made it too long, so here it is on its own.

Let me interject a personal note first. I was at NASA’s Goddard Space Flight Center working on Hubble when STEREO was first being put together as a mission. I remember thinking how cool it would be to see the entire Sun at the same time, and what it would mean to my friends over at the heliospheric physics section. I have a decent imagination, but still there was no way I could’ve ever foreseen some of the things STEREO has brought us — Nature is always more clever than any one of us. And my favorite of all of them, sent back while the two spacecraft were still relatively near the Earth, is this incredible animation showing something that can never be seen from Earth: the tiny disk of the Moon transiting the Sun:

From Earth, that would be a solar eclipse, where the black disk of the Moon would look the same size as the bright Sun. But from well over a million kilometers away — the distance STEREO B was when it took these images — the Moon is smaller, providing this eerie and beautiful view that is a stunning reminder that humans are a spacefaring species, and the views we get from there expand our world.

MORE ABOUT: eclipse, Moon, STEREO, Sun, transit

Comments (21)

  1. humans are a spacefaring species

    I only wish we were moreso a spacefaring species instead of only a very few of us with vast resources to dedicate to it.

  2. From Earth, that would be a solar eclipse, where the black disk of the Moon would look the same size as the bright Sun.

    Well, we do have annular eclipses, but that’s not quite the same thing as this video. (Which, by the way, I remember seeing the first time you posted it. Has it really been nearly 4 years?)

    But, you know what would have topped that, if things had lined up “better”? Both the Earth and the Moon transiting the Sun at the same time, or in quick succession.

  3. Wow! Fantastic video of an eclipse. I’d never seen that before.

  4. Stan Taylor
  5. Keith Bowden

    Still no sign of Counter-Earth? Man, what’s the High Evolutionary up to…?

    Seriously, do we have further probes scheduled for launch so that we can maintain a 360° view of the sun beyond the next 8 years?

  6. CB

    On the down side no Counter-Earth. On the plus side no Gor. Let’s call it a wash.

  7. Naomi

    Neat! Although, huh. What’s the size threshold which says whether something is an annular eclipse or a transit? If it was a bit bigger, would it be called an eclipse from this vantage point?

    Also! What’s your take on this video? People are saying it’s one of the four horsemen of the apocalype, but I think it looks more like an upside down reflection of the flames (especially since it moves with the camera).

  8. Chris A.

    “But from well over a million kilometers away…the Moon is smaller…”

    Of course, the sun is smaller too. Just not as much. :)

  9. Chris A.

    @#7 (Naomi):
    Yep–it’s an internal reflection in the video camera’s optics. The dead giveaway, as you noted, is that its motion is tied to the camera’s motion.

    More specifically, it moves in a way that keeps it exactly diametrically opposed to the flames through the lens’s center (i.e., its position relative to the lens center, in polar coordinates, is THETA (“horseman”) = THETA(flame) + 180 and R(“horseman”) = R(flame)).

    Congratulations, Naomi–your baloney filter is working properly.

    To those who are convinced that it really is the “horseman”, all I can say is: “Oh pareidolia-plus-ignorance-of-optics, is there anything you _can’t_ see?”

  10. Messier Tidy Upper

    Great video. You can repeat that one again anytime BA, I love it, thanks. 8)

    @8. Chris A. :

    “But from well over a million kilometers away…the Moon is smaller…” Of course, the sun is smaller too. Just not as much.

    Actually they both remain the same size – it just doesn’t appear that way from the varying distances! 😉

    Well, our Moon *is* shrinking slightly but not so much that you’d notice. Actually, the Sun is shrinking too – losing mass in the form of the solar wind and via the conversion of mass into energy at the core but, again, not so much that we can detect it visually. 😉

  11. Messier Tidy Upper

    For more about our shrinking Moon – click on :

    & Moon

    & on it shrinking and growing in phase and caught on camera :


    “The triple triumph of the Moon, then, is that it made it possible for man [sic] to exist; it made it possible for him [sic] to develop mathematics and science, it made it possible for him [sic] to transcend Earth and conquer space.”
    – Page 38, ‘The Tragedy of the Moon’, Isaac Asimov, Mercury Press, 1972.

    “This is surreal, how each grain of moondust falls into place in these little fans, almost like rose petals.”
    – Buzz Aldrin (during his first Moonwalk, July 1969), Page 38, ‘Magnificent Desolation’, B. Aldrin, Bloomsbury, 2009.

    Our Sun’s brightness is gradually increasing by about 10 % every billion years.
    – McNab, David & Younger, James, ‘The Planets’, BBC Worldwide,1999.

    [In one of those delightful astronomical paradoxes, the more our Sun burns up its fuel and loses mass the hotter, brighter and larger it gets – up to a point and whilst it remains on the core-hydrogen burning main sequence anyhow – Ed.] :-)

  12. Thameron

    humans are a spacefaring species

    If you count low Earth orbit as ‘Space’ then yeah I suppose so, the same way swimmers and surfers might be said to be ocean faring.

  13. Vaishnavi

    ‘Nature is always more clever than any one of us’

    You nailed that one right on the head.

  14. Astrojunkie

    I’ve worked STEREO from the non-civil servant side of things for several years, and I have to say it’s been one of the best experiences I’ve ever had. Between all the great data it’s sent back and the awesome people who work in mission ops, I don’t think we could ask for anything more. It sometimes takes a back seat to the flashier SOHO and SDO imagery, but STEREO has proven to be a low-maintenance work horse that is perfectly situated to produce incredible data for years to come. I’m exceptionally proud to be part of that.

    Thanks for sharing, Phil.

  15. Hector

    Phil you may want to know that today instead of the usal feed with your articles I got garbage in my in-box.

    Perhaps there is some problem with, either way I though you should know.



  16. Pete Jackson

    The moon was in first quarter phase as seen from the Earth on 2007/02/24 at 07:57 UT, so the Earth is way off to the upper right at the time of this video, something like about 18 degrees or 36 solar diameters. I wonder if there are any videos of Earth transits, or perhaps they avoided these by maneuvering the spacecraft?

  17. OtherRob

    @Thameron, #12

    humans are a spacefaring species

    If you count low Earth orbit as ‘Space’ then yeah I suppose so, the same way swimmers and surfers might be said to be ocean faring.

    I think that what Phil is saying here is that we are a spacefaring species in every possible sense of the word. It’s just that our “ship” happens to be the size of a planet. :)

    I think that for a lot of people Earth and “space” are separate. We are here on Earth and space is “out there”. I suspect that many folk — excluding those here, of course 😉 — don’t regularly think of the Earth as just another body moving through space. Heck, it’s not something I think about all that often. And videos like this are a great reminder.

  18. That’s a pretty fantastic video. It reminds me of the movie Sunshine just simply by the way it looks. Apparently that movie did a good job capturing what an event similar to this would look like.

  19. I was just thinking about this and I realized there was something I don’t understand…

    How is it that the moon ended up between the sapcecraft and the sun? Isn’t it within the same orbit as earth but 290 million miles away? Since the moon’s orbit is only ~250k miles, how did it end up in the middle? Or is STEREO in a wider orbit but in the same general region as Earth? I think I need a diagram showing their position…

  20. Pete Jackson

    @19Endyo. The video of the Moon transit was taken more than 3 years ago when Stereo B was much closer to the Earth than it is now.

  21. Wow how did I not notice that…


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