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April 30, A well-timed shot of the Hubble Space Telescope and the space shuttle Atlantis in , as they transited the sun together in just 0. Credit: NASA. Watching Hubble track across the Earth. Credit: N2YO. Source: The Conversation.
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Chemists discover new way to harness energy from ammonia 33 minutes ago. Reading Paper on Earth Occultation Technique 16 hours ago. Level of details in prime focus vs eyepiece images 22 hours ago.
Maximum mass of a neutron star Nov 09, Observational bias? Lack of massive black hole observations Nov 09, Is the Sun a low-mass star or a medium-mass star? All of these assumptions must hold true in order for the pattern of light presently coming from the photo to represent the appearance of your daughter ten years ago.
For instance, suppose a bit of acid drops on the photo and causes a big white dot to appear above your daughter's head. If you were literally looking back in time when looking at the photo, you would have to conclude that there was a UFO or ball lightning hovering above your girl's head ten years ago.
But you are likely smart enough to realize that you are not literally looking back in time, but are simply looking at a present-time pattern of light which no longer exactly represents the pattern of light ten years ago when you took the photo. Similarly, the present-time beams of light hitting telescopes that are pointed at distant galaxies only give us information about the past insofar as the light has not changed over the years. More realistically, the light from distant galaxies can change as is travels, but it has to change in ways that we can understand and subtract out if we are to end up with an accurate representation of the past.
One major change that happens to light traveling through intergalactic space is that the light is redshifted because of the expansion of the universe.
As light travels through space, which is itself expanding, the light wave gets stretched and ends up with longer wavelength components. Longer wavelengths means that the entire light pattern is shifted towards the color red on the visible spectrum. Therefore, the present-time bundle of light hitting a telescope does not exactly match the appearance of the distant galaxy that first created the light millions of years ago; it is redder.
Yes, it is true. During its first three years Hubble suffered from what is known as spherical aberration. Spherical aberration is an optical defect and Hubble's main mirror is two microns too flat. The problem was caused by a faulty measuring device used during the process of polishing the mirror. Hubble has made a series of very deep observations taken in very dark parts of the sky. Like using a long exposure on a digital camera, these long exposure shots up to several weeks reveal very faint details that are not normally visible in shorter exposures.
Hubble's so-called angular resolution — or sharpness — is measured as the smallest angle on the sky that it can resolve i. Quite impressive! But Hubble would have to look down through the atmosphere, which would blur the images and make the actual resolution worse. In addition, Hubble orbits the Earth at such a rate that any image it took would be blurred by the motion.
In the past Hubble was pointed towards Earth several times to calibrate some of its instruments. JWST will not be a like-for-like replacement of Hubble. The biggest difference is that it will be optimised for observing infrared light with limited visible light capabilities , while Hubble is optimised for visible and UV light with limited infrared capabilities. This means it will be better at looking through dust and gas clouds, which is useful for studying star formation.
It will also be much better for studying highly redshifted objects, and is therefore expected to make major contributions to the study of the very early Universe. This is a bit difficult to explain in just a few sentences. Hubble has measured the age and size of the Universe better than before by refining the value for the Hubble constant, which is related to the expansion rate of the Universe. It has also seen details which are not visible from the ground in the first galaxies.
Today we know that galaxies were formed earlier than previously thought and most scientists also believe that they evolve by colliding and merging together. There have been a few cases where Hubble has been aimed at the Moon - see here. This has to be done with the greatest care since the Moon is very bright , and is normally avoided.
To see the surface of the Moon in enough detail, you simply need to get nearer to the lunar surface than Hubble is Hubble is not significantly closer to the Moon than we are here on Earth. The Apollo landing sites are visible in these observations. See the images here and here. Firstly we should say that a bright, high-contrast feature such as a star can be seen however small in angular terms it appears.
In these cases the star would just appear as a dot. So, if there were a very shiny surface on the Moon that caught the Sun, it might be seen from Earth with quite a small telescope. Here we will try to answer the related question of how close together two features can be and still be discerned as separate — this is called the angular resolution.
The telescope diameter, D, is also in metres. Note that the resolution gets better at shorter wavelengths, so we will use the second of these numbers from now on. However, the detectors have pixels that are quite large relative to these values in most cases and this degrades the resolution somewhat. So for Hubble, we conclude that the best resolution we are likely to manage is about 0. Unfortunately it is very difficult for Hubble to observe the Moon — because the telescope is rapidly orbiting the Earth the Moon appears to swing backwards and forwards in the sky very rapidly and it is almost impossible for the telescope to compensate — so it is unlikely that this limit could ever be approached.
The similarity of the expansion of the Universe to a conventional blast is a typical misconception in the popularisations of the cosmological model, possibly due to the unfortunate choice of the name Big Bang. The expansion of the Universe is totally different from a conventional blast, which happens within a given space. The expansion of the Universe is the expansion of spacetime itself, together with its energy—matter content.
Admittedly it is not easy to imagine the correct scenario, because it is so different from our experience of everyday life. Therefore, if we look at objects which are at some distance from us, we see them as they were sometime ago, the elapsed time being exactly the time needed by the light to reach us.
For example, the most recent image of the surface of the Sun that we can observe is always at least eight minutes old, because it takes about eight minutes for sunlight to reach the Earth. If you look at the stars in the constellation of Orion, which are roughly at a distance of — light-years, you see them as they were — years ago.
If some of them exploded today as supernovae, we or our descendents! This explains we hope why we can see pictures of the very old Universe: we just have to have powerful enough telescopes to look very far away.
The telescope whizzes around Earth at 28 kilometres an hour, taking just 96 minutes to complete one orbit of our planet. Like any modern telescope, Hubble captures images on a digital device that transforms photons into electrons; and the latter carry no colour information. However, filters placed in front of the camera only allow for specific kinds of light blue or green light, infrared light or ultraviolet radiation to pass through them and into the camera.
Therefore, most of the images found on spacetelescope. To create the final image, these individual images are coloured — depending on the type of light they represent — and then combined with the others.
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