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My congrats to the Herschel and Planck spacecraft teams for the successful launch of their missions! With all the news about Hubble right now, it’s easy to let it slip by, but these are very ambitious missions run by the European Space Agency, and will contribute mightily to our knowledge of the Universe, how it got started, and what’s in it now.
More astronomy, more science! I’m all for that.
If you went to BadAstronomy.com and found yourself here, never fear: the BA Blog has moved to its new home at Discover Blogs. The original BA site (with the Moon Hoax debunking and all that) is still online, too.
Phil Plait, the creator of Bad Astronomy, is an astronomer, lecturer, and author. After ten years working on Hubble Space Telescope and six more working on astronomy education, he struck out on his own as a writer. He has written two books, dozens of magazine articles, and 12 bazillion blog articles. He is a skeptic, and fights misuses of science as well as praising the wonder of real science.
Contact me: The Bad Astronomer "at" gmail "dot" com
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"Reading this book is like getting punched in the face by Carl Sagan. Frightening, but oddly exhilarating."
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May 14th, 2009 at 1:39 pm
Well done ESA!
I am really looking forward to peering back at the very origins!
May 14th, 2009 at 1:42 pm
Phil,
The ESA webpage says that the spacecraft will travel to and ORBIT the L2 Lagrange point. Not orbit at that point, it says will orbit the L2 Lagrange point. They even have a nifty little animation showing the path to get there and the orbit once at L2.
How can a spacecraft orbit a virtual point in space?
Thanks
May 14th, 2009 at 1:51 pm
Awesome! My congratulatiosn tothe Herschel &Planck teams and best regards for them and their observatories
Superluminous (beyond brilliant) news there BA -thanks for letting us know.
Oh & thanks too BA for your Hubble Top 10 – this time I didn’t know many of those at all.
May 14th, 2009 at 1:59 pm
How can a spacecraft orbit a virtual point in space?
By literally making pin point manouvres maybe?
Or by pointing the right way?
Hmm… how big apoint is depends on your scale and point (ha ha) of veiw – a singularity is a (sub?)microscopic point with the mass of at least three Suns (primordial Black Holes execpted -& we don’t even know if they exist.)
A star is a point of light in the sky – even the largest ones like Betelgeux, Antares & VV Cephei.
A point is made by the point of a pencil or needle – or argument.
So as often the case the answer is .. well it depends.
But maybe I’ve just missed your point.
——
How many angels can dance on the head of a pin?
As many as want to.
– Byron (telepath hero), ‘Babylon -5.
May 14th, 2009 at 2:03 pm
They also mentioned “quasi-orbits” during launch. AFAIU the Lagrange ‘points’ are volumes of potentially “flat space” due to balanced gravity forces. They aren’t “virtual” in the sense that, say, a black hole event horizon is.
[The horizon is the "point of no return" for a photon of light, but an infalling body doesn't have any way of observing that. Turns out the event horizon is an emergent property of the system. But here it is immediately apparent that space is flat.]
Even if most volumes are unstable equilibriums (they are only balanced in one direction) they permit fuel-saving trajectories.
May 14th, 2009 at 2:30 pm
Cool news! With the launch of the LRO next month we ought to be seeing a lot of nifty space science stuff in the coming months and years.
May 14th, 2009 at 2:33 pm
I already shared this story at UniverseToday, I also want to leave it here
I watched the launch, too, at the ESA-site. The timing was a little bad. At that time I was sitting in a lecture at university about the inner structure of stars. But since this is only a “minor” lecture with only four students (including me) attending I ask the lecturer and he gave his permission that I could follow the launch on my laptop silently.
That was a different lecture than what I am used to
But I am very happy that it was such a succesful launch. Can’t wait for their first results! They gonna be awesome!
May 14th, 2009 at 3:01 pm
About the “orbit”:
Lagrangian points are points of equilibrium in a two-body system (such as Earth and Sun). There are 5 of them. Some have stable equilibrium (a “valley”), others (like L2) have an unstable equilbrium (a “hilltop”). That’s why they won’t stay exactly on L2: being there, the only thing you can be sure is you’ll fall aside. Instead, they orbit around it; but being in a place where gravitatonal forces are *almost* zero reduces the power required for attitude and position control. Finally, these orbits are not going to be ellipses like we are used to, but Lissajous figures (you know, those funny shapes on the oscylloscope of every sci-fi B-movie).
May 14th, 2009 at 3:45 pm
I was a bit on edge as launch time approached. Wow, two expensive and complex observatories on one rocket!
With the two instruments now safely on their way to station I can relax. And wait the two months till data begins to flow.
May 14th, 2009 at 3:48 pm
No comment for this one!
May 14th, 2009 at 3:55 pm
I’d say that this has been a good month for orbital telescopes.
May 14th, 2009 at 4:54 pm
Hmm, a few people seem a little confused by what a Lagrange point is, I suggest reading the Wikipedia article: http://en.wikipedia.org/wiki/Lagrange_point
In essence, they are points where the gravitational forces of two large bodies (in this case, the Sun and the Earth) balances the “centrifugal force” on a body orbiting with the same period as the two masses. Most of these are unstable (i.e. if you get displaced from the exact spot, you feel a force moving you further away) but a couple as stable.
The article will tell you more.
May 14th, 2009 at 5:58 pm
Yay! Now for the test and commisioning phase … but success at that stage is far greater than the success rate of a launch.
May 14th, 2009 at 7:31 pm
Hey Phil, a couple of months ago, I read and reviewed “Bad Astronomy” on my nonfiction book review site, and I left on a comment on this site saying that I was going to read and review “Death from the Skies” on my site too. Well, I just finished reading and reviewing the book – feel free to check out the review on my site. HINT: I loved the book. A lot. A whole lot.
Have I mentioned yet that I think this book rocks?
Anyway, just had to tell you that I followed through on my promise.
I going to school to become an elementary ed teacher, and the grades I’d love to teach is anywhere from 4th to 6th grade. I can already tell you that I will be using some of your book in my classroom. Your book makes astronomy interesting, while the “standard” science textbook for elementary grades makes even an astronomy enthusiast want to take a long nap. So I fully plan on making my lessons a hell of a lot more interesting and exciting, and one of those ways of livening things up will be with your book.
Thanks again for the fantastic book,
Hava
May 14th, 2009 at 7:49 pm
@Astronomynut
Google “Interplanetary Superhighway” if I haven’t explained the concepts well enough. Past halo orbits, my intuition is hanging by the skin of its teeth.
Lagrange points are the places in space where the gravity of two objects adds or subtracts just right to keep a third (the satellite) in an orbit it wouldn’t ordinarily be able to maintain. For L1, L2, and L3, the ones in a line drawn through the other two, Sun and Earth in this case, it’s usually explained like the nearer object is pulling on the satellite to allow it to orbit at a speed that keeps it in that line. Specifically, with L2, which lies on the far side of the Earth, the Earth is pulling down because if the satellite was going around the sun that fast it would zoom out to a farther orbit and slow down relative to Earth.
To understand a Halo orbit, a Lyapunov orbit, and a Lissajou orbit, you need to add some dimensions beyond a line. If you think of the Earth having the satellite on a leash, it gets a bit clearer. At L1, the satellite is orbiting closer to the Sun than Earth and would naturally want to go around faster than Earth. At L2, the satellite is orbiting farther than Earth and would naturally want to go around slower than Earth. The Earth uses its gravity to tug it around at the same speed. If you plotted this out, the satellite would need more energy to move out away from the Sun-Earth line and this energy curve would look like a U shape PERPENDICULAR TO the Sun-Earth line, so it settles back to the bottom of the U right on the Sun-Earth line. This is the ’stable’ part of quasi-stable.
If you look at the satellite’s tendency ALONG the Sun-Earth line, though, It’s actually an upside down U (or lower case n, sans serif). That is, if you move the satellite just slightly closer or further to the Sun than the sweet spot it quickly moves even further away from the sweet spot. This is why it is quasi-stable, it is only stable in one direction. In fact, putting the two curves together in three dimensions, you wind up with a saddle shape with the spine along the orbital path. As long as the satellite is on the spine of the saddle everything is fine, but it’s like balancing a marble on a saddle. It’s really fiddly.
But, if you take that saddle and attach it to a string anchored at you sweet spot and swing it around perpendicular to the Sun-Earth line (i.e. add a bit of centripetal motion) you wind up with what describes the possible paths of the satellite in an orbit around the sweet spot. The length of the string is the size of the orbit. Blur that out and it looks like the inside of a donut. The larger the donut, the flatter the saddle is. So adding that bit of motion around the sweet spot makes it easier to maintain your position along the Sun-Earth line. And the orbit looking from a place along the Sun-Earth line looks like a halo projected against the stars. Thus, the name. In three dimensions, though, it looks like a ring that’s been hammered against a sphere the size of the Lagrange point’s orbit around the Sun.
A Lyapunov orbit is the same sort of idea but the orbit lies within the plane of the Earth’s orbit around the Sun, the varying speed of the orbit pulls it back up the saddle. A Lissajou orbit is essentially a hybrid of the two that moves both out of the plane of Earth’s orbit and in and out along (but not on) the Sun-Earth line.
I think that last bit’s right.
May 15th, 2009 at 6:39 am
All,
Thanks for all the input. I understood about the L2 point and the station keeping required. I guess it’s the animation that is the most confusing that is found at
http://www.esa.int/SPECIALS/herschelplanck/SEMVW10YDUF_1.html#subhead4
It shows the satellite orbiting the L2 point at some huge distance. Looks to be greater than the orbit of the moon around the Earth. Maybe if the animation continued longer, the “orbit would condense to a very small station keeping orbit.
May 15th, 2009 at 1:00 pm
[...] the European Space Agency successfully launched the space observatories Herschel and Planck. Today, they released two cool videos of the event: one was taken by the spacecraft itself and [...]
May 16th, 2009 at 1:26 am
@ QUASAR: (May 14th, 2009 at 3:48 pm) “No comment for this one!”
That sentence is a lie!
@ Flying sardines: (May 14th, 2009 at 1:59 pm )
Ironically enough, some people would consider your post there to be pointless!
May 16th, 2009 at 1:40 am
Markle, if you think it’s hard balancing a marble on a saddle, you should try balancing an egg. On end.. On the equinox… Oops, a month late. Never mind. Go Planck and Herschel!
October 9th, 2009 at 7:25 pm
[...] As you may know, European Space Agency (ESA) launched on 14th May with Ariane spacecraft the two space observatories Herschel and Planck. [...]