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View Full Version : How can the hubble see so far away, but not at near things?



Knowledge_Seeker
2006-Aug-10, 07:34 PM
Why is it that the Hubble is able to view objects, stars, galaxies, and such that are many light years away, but it cannot see the surface of the moon, pluto, and 2003 UB313 with any clarity at all?

cmsavage
2006-Aug-10, 09:04 PM
The Hubble's resolution limits its ability to view both pluto and 2003 UB313, as these are very small objects. To Hubble, they are essentially point sources just like more distant stars (these objects are at the very limit of Hubble's ability to resolve). In fact, the Hubble picture of 2003 UB313 really looks no different than a star.

Hubble is good at observing faint objects, such as distant galaxies. These galaxies are much wider than a star and can be resolved, leading to the very nice Hubble images you typically see. For instance, this image (http://imgsrc.hubblesite.org/hu/db/2006/24/images/a/formats/web_print.jpg) is of a galaxy that appears more than 1,000 times wider in our sky than pluto does.

Keep in mind that we have very good telescopes on the ground, some of which have much better resolution than Hubble. Using Hubble to image the moon would be a waste of its valuable time as these ground based telescopes can do so much better.

Nowhere Man
2006-Aug-10, 10:41 PM
And Hubble has imaged the moon. (http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/14/image/) But why do it more than once?

Fred

Knowledge_Seeker
2006-Aug-10, 11:45 PM
CMSAVAGE - im talking about a close up view of the pluto and 2003 UB313, so u call this a star-like view?

http://imgsrc.hubblesite.org/hu/db/2006/16/images/b/formats/web.jpg

NOWHERE MAN - im talking about close up view where the apollo missions landed. because with the whole fake moon landing thing some say until we get pictures from the moon that shows the remains of the apollo missions, they dont believe.

Hamlet
2006-Aug-10, 11:53 PM
CMSAVAGE - im talking about a close up view of the pluto and 2003 UB313, so u call this a star-like view?

http://imgsrc.hubblesite.org/hu/db/2006/16/images/b/formats/web.jpg

NOWHERE MAN - im talking about close up view where the apollo missions landed. because with the whole fake moon landing thing some say until we get pictures from the moon that shows the remains of the apollo missions, they dont believe.

Hubble doesn't have the resolution to view any Apollo artifacts. Here's (http://hubblesite.org/reference_desk/faq/answer.php.id=77&cat=topten) a link that has some info. You should also try searching the BAUT forum. This topic has come up numerous times and the answers there may help you.

Pluto or 2003 UB313 are just too small to be resolved in any detail by Hubble.

Hoax believers don't base there beliefs on evidence, so showing them images from a telescope or probe is not going to convince them. They would just claim these images were faked as well.

Kaptain K
2006-Aug-11, 12:02 AM
Knowledge_Seeker,

Resolution is a function of the diameter of a telescope's objective element (mirror or lens). The Hubble is only 2.4 meters in diameter. Its resolution is about 0.1 arc seconds. The Moon is ~1800 arc seconds across and ~2000 miles across. Do the math... the best the Hubble can do on the Moon is about a half a mile.
Pluto is even worse. It is half the size of the Moon and 4000 times as far away!

cmsavage
2006-Aug-11, 01:07 AM
CMSAVAGE - im talking about a close up view of the pluto and 2003 UB313, so u call this a star-like view?
That image is zoomed so far in that you can see the pixels (each box). Take any Hubble picture that contains a star, zoom in on that star and it will look about the same.

In fact, I am attaching a random star from this field of view (http://imgsrc.hubblesite.org/hu/db/2006/24/images/a/formats/web_print.jpg), zoomed at x20. You can see the same pixelation. This is the same "close up view" that the 2003 UB313 image is. Actually, the planet has more pixels than the star, so it is actually a better image.

ToSeek
2006-Aug-11, 01:57 AM
Galaxies can be tens of arcseconds in diameter (and much more for nearby ones), while Pluto, for example, is only about a tenth of an arcsecond in diameter.

AGN Fuel
2006-Aug-11, 03:07 AM
CMSAVAGE - im talking about a close up view of the pluto and 2003 UB313, so u call this a star-like view?

http://imgsrc.hubblesite.org/hu/db/2006/16/images/b/formats/web.jpg

NOWHERE MAN - im talking about close up view where the apollo missions landed. because with the whole fake moon landing thing some say until we get pictures from the moon that shows the remains of the apollo missions, they dont believe.


One thing to keep in mind is that the public perception of the Hubble Space Telescope is that it is some super-dooper strong telescope that could read newsprint at a gazillion miles if you turned it up enough. Needless to say, it doesn't work like that!

The resolution of a telescope (which is what enables you to see the surface details on Pluto) depends on the diameter of the primary mirror in the telescope. In terms of this, the Hubble is actually rather puny, with a primary mirror only 2.4 metres in diameter. In comparison, there are a number of telescopes on Earth that have primary mirrors over 4 times larger (i.e. >16 times greater surface area to catch light)! So in terms of pure resolution, the HST is (theoretically anyway) rather ordinary.

So this raises 2 further questions: why can't these giant Earthbound telescope image details on Pluto, and what makes the HST so special then, if it is so small?

The answer to the first question is that, fortunately for our ability to live, we live at the bottom of a sea of air - the atmosphere. While this is handy for allowing us to breathe, it is a bit of a nuisance for astronomers trying to look through it. This is because as the light from an object passes through the atmosphere, it gets refracted as it passes through atmospheric cells until the point-like image becomes 'smeared out'. You have seen the effect for yourself whenever you look at a twinkling star low to the horizon. Even with Adaptive Optics, which help overcome the problem, we still don't get good enough resolution even with the big scopes to read 'The Pluto Times'.

So what about the HST? Well, even though it is (relatively) small, it has two major advantages over an Earthbound telescope. Firstly, it is above the atmosphere and so it doesn't get affected by the 'twinkling' refraction. Secondly, because it is in space, it is not bound by the rotation of the Earth to limited exposure times. As a result, astronomers can train HST on an object and allow it to collect light from that object for days if needed.

This long 'integration' allows the HST to observe very faint objects (and by association, extremely distant objects). It is this ability that gives rise to HST being such an important instrument. However, it is still limited by a small primary mirror, so high resolution on small objects (such as Pluto or the Apollo landing sites) is not within its capabilities.

Tim Thompson
2006-Aug-11, 05:03 AM
It certainly looks to me like Hubble can see Pluto just fine (http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/09/). The image linked by Knowledge_Seeker is 2003 UB313 (http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/16/image/b). As the page points out, at a distance of about 10 billion miles, it is only 1.5 pixels across. Hubble can see near things (http://hubblesite.org/newscenter/newsdesk/archive/releases/category/solar%20system/) quite well. But 2003 UB313 (http://www.gps.caltech.edu/~mbrown/planetlila/) is just too small (and the HST (http://www.stsci.edu/hst/) is not very large either).

AGN Fuel
2006-Aug-11, 05:30 AM
im talking about a close up view of the pluto and 2003 UB313

I'm not sure that Knowledge_Seeker would feel those images meet requirement.

cmsavage
2006-Aug-11, 06:12 AM
It certainly looks to me like Hubble can see Pluto just fine (http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/09/).
Thanks Tim. Lest anyone fails to read the description on that page, the large (bottom) images are computer processed reconstructions, the small (top) images are the true Hubble images: only about 10 pixels across and not much better than 2003 UB313.

Tim Thompson
2006-Aug-11, 03:04 PM
Thanks Tim. Lest anyone fails to read the description on that page, the large (bottom) images are computer processed reconstructions, the small (top) images are the true Hubble images: only about 10 pixels across and not much better than 2003 UB313.

Ah, but remember ...


Hubble Reveals Surface of Pluto for First Time (http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/09/text/):
"This team of planetary scientists used the FOC aboard the Hubble to obtain over a dozen high-quality visible and ultraviolet images of Pluto in mid-1994. These images have now been carefully reduced and analyzed."

Since Pluto is about 10 pixels across, one can'nudge the telescope around by angular shifts that are smaller then one pixel. That way you make a set of images which contains real information on a sub-pixel scale, and that means you can use those images to synthesize a collective image with smaller pixels, but real information. That's what the computer processing does, and that seriously counts as HST "seeing" Pluto. It just takes more than one single image. That is in fact how almost every image you ever see from any telescope is made, these days anyway. As another trick, you can use deconvolution methods to take out the effect of the point spread function for the telescope, but that is a lot less straight forward to do. I don't know if that was done to the Pluto images.

2003 UB313, being hardly larger than a pixel, is much too small for that trick to work.

cmsavage
2006-Aug-11, 05:46 PM
Is that really the case here? Doesn't that only work if the pixel size is larger than the resolution of the optics?

Knowledge_Seeker
2006-Aug-11, 09:28 PM
i seem to understand now.... [with some confusion]