Hi there. I've been pondering about the "blind spot" that exists between the Earth and the Sun, and I have a few questions.

From what I understand (and please correct me if I'm wrong), the blind spot is, basically, the "day side" of Earth. You can't really use a telescope during the day from Earth, because the sun overpowers everything else. If you put a telescope into orbit, the blind spot is much smaller, since you don't have atmosphere to contend with. However, there will still be a good arc of the sky that you woulnd't be able to look at, because that sky is directly between the telescope and the sun.

The blind spot is big enough that astronomers worry about planetkiller sized rocks sneaking up on Earth in it.

So, my questions are:

1) How big of an arc of sky is the blind spot (from the point of view of a telescope in orbit)?

2) Since a total solar eclipse occurs when the moon passes between the sun and the Earth at just the right angle, does that mean that the moon is in the blind spot at that moment?

3) If so, lets say something is launched from the moon at that moment. (A ship, for example). If that object moves directly to Earth (or, more appropriately, plots the shortest course possible so that it and the Earth intersect the same part of Earth's orbit at the same time...), will it be in the blind spot for the whole journey?

Also, if anyone has any web sites / web pages about the blind spot, I'd appreciate them. I can't seem to find much specific information about it. (There isn't even a wikipedia entry! =( )

Thanks so much!

Sorry, I can't answer the first question. But the answer to the second one would be yes.

I think that would be possible. It would make an interesting premise for a science fiction novel, but in practice it's not all that important. If you wanted to launch a surprise attack, there are much easier ways to do it than taking the trouble of launching something from the moon!

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As above, so below

Check out the SOHO images:

http://sohowww.nascom.nasa.gov/

Specifically, the ones that show the sky in the vicinity of the Sun. It is common nowadays for comets to be discovered first in those images.

Coronagraph is how something like this can be done from Earth:

http://umbra.nascom.nasa.gov/images/latest_mk4.gif

Certainly there isn't a blind spot between Earth and the Sun, as SOHO proves. Despite what the PX believers say. Presumably then there isn't a blind spot between the Earth and the moon either, although I'm afraid I can't confirm that.

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It depends on the scope and the sensitivity of the instruments. The HST can not get within 50 deg. of the sun without risk of damage. It is limited to 15 deg. of the Earth and Moon. However, it has imaged the moon, but carefully no doubt.

I got this from... here

I do not know how well SOHO, TRACE and others which can observe the sun/corona would handle an asteroid.

I could be wrong, but I don't think SOHO extends to 50 deg from the Sun. Of course, other space scopes probably are not as limited as Hubble.


I'll assume you are not an alien scout :wink: . Ground based scopes would have no problem with glare. Even if they did, the moon isn't big enough to provide glare for much of the trip. Observers at various locations would see the ship offset from the moon.

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Lighten up! This is a stellar board!

If two 'Hubble' telescopes were parked at the L1 points in Earth's orbit about the sun there would be no blind spot so if there were a serious perceived problem this would be one way to overcome it.

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By asking questions we sometimes get the wrong answers, from wrong answers we learn to ask the right questions.

SOHO LASCO C3 FOV is about 19 degrees in diameter. It can see down to about 6.5 mag or so near the outer edges.

Gaia will build a 3D pic of the stars, probe the blind spot and hunt for extra solar worlds
http://www.spacedaily.com/news/deepimpact-02g.html
ESA's Gaia spacecraft will be ideally situated to probe the asteroid blind spot between the Sun and Earth.

Orbital mechanics preclude the possibility of anything coming at us from the sun's "blind spot" remaining in the blind spot very long, and certainly not long enough to be on a collision course.

Unless the velocity is on the order of a million miles per second...

Edit: Accidently wrote "astrologer" instead of "astronomer". Oops!

[quote="Jens"]I have to admit, I was thinking of "surprise". (In answer to another's question... no I'm not an alien invader. Just a humble SF author ).

Specifically, getting a whole bunch of stuff into orbit. The reason why I was thinking the moon was:

1) It would take ~a month to construct the objects
2) Doing it on Earth might get it noticed
3) If not noticed during construction, then launching them from Earth WOULD get noticed (after the first few hundred, anyways)
4) Building them on the far side of the moon means that no one is watching the construction. (From what I understand, there are only a few ways to observing what's happening on the far side of the moon, and the US government does, or theoretically can, control all of them)
5) Launching them from the moon would be much easier, since part of the construction would include a large, magnetic rail-launch system.

Now, the only problem I have is that once they round the moon and head towards Earth, everyone observatory, amature astronomer and (more importantly) government with anti-satellite capabilites will be watching. And they'll all have a large number of days to protest/shoot down the approaching orbiters.

So, I was wondering how to get them from the Moon to the Earth. I read about the blind spot, and how small objects (these things are only a few feet in diameter) get lost in it. The moon would continue its orbit and move out of the blind spot, but the objects would continue on towards Earth in the blind spot.

It's okay if they're spotted a day or less from orbit, since by then it will be too late for anyone to react.