FAQ - Frequently Asked Questions
The first six questions
By using the button "contact" below you can send questions to the Hubble Europeans Space Agency Information Centre. Some of the best questions and answers will be selected for publication on the page below.
1. Q: I heard that Hubble had problems in its first years. What really happened?
A: Yes, it is true. Hubble suffered from what is known as spherical aberration during its first three years. Spherical aberration is an optical defect and put simply, Hubble's main mirror has a perfect shape, but is two microns too flat. The problem was caused by a faulty measuring device used during the polishing. During the First Servicing Mission the problem was repaired by installing an extra optical device in Hubble called COSTAR. The spherical aberration in Hubble's main mirror is still there, but today it does not affect the observations - partly due to COSTAR and partly due to built-in optical corrections in the newer instruments.
2. Q: How much has the Hubble Telescope cost overall so far?
A: As you may know Hubble is a collaboration between ESA and NASA. ESA has 15% of the observing time and Europe's financial contribution to Hubble is 593 million Euros at in1999 terms (including the development of FOC and the Solar Arrays, the participation in the operations and in the relevant Servicing Missions). The US expenditure is currently an estimated 4.5 billion US$.
3. Q: How is Hubble in 2005 going to be better than it is now?
A: Mainly due to new science instruments: In 2001 a wonderful new instrument, the Advanced Camera for Surveys (ACS) will be installed with higher resolution and a larger field of view (larger area on the sky). Also the Near Infrared Camera and Multi-Object Spectrograph (NICMOS) Cooling System will be installed. This will enable NICMOS to work again giving Hubble excellent infrared vision. In 2003 the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3) will be installed. Both instruments are long awaited by the scientists. Read more under "About Hubble" and "Instruments" and "Future Servicing Missions".
4. Q: What do you think is Hubble's best photo so far?
A: Oh - that is almost a naughty question ;-) Hubble has produced so many fantastic pictures. And to tell you the truth: I change my taste once in a while. These days it is the Keyhole Nebula which is my favourite.
5. Q: Why is Hubble able to see so much better than telescopes on earth?
A: Because it is above the Earth's atmosphere. The atmosphere disturbs the starlight (a bit like looking through water) and blurs the images. So Hubble's images are much sharper images from other telescopes.
6. Q: What has the Hubble Space Telescope found out about the beginning of the universe?
A: It is a bit difficult to state in just a few sentences. Hubble has measured the age and size of the Universe better than before (by refining value for the Hubble constant - or the expansion rate). It has also seen details in the first galaxies that are not visible from the ground. Today we know that galaxies were formed earlier than previously thought and most scientists also believe that they evolve by colliding and merging together.
The next six questions
7. Q: What is the Hubble deep space field?
A: That is two very long (> 100 hours) exposures showing details in the remote Universe never seen before. I can recommend reading the new 10 year brochure that is also available on the web (under "Further information").
8. Q: What is going to be so much better about the NGST?
A: The Next Generation Space Telescope will be much larger than Hubble - it will be able to collect ten times more light than Hubble and thus see much fainter objects. A special feature is that it will mainly be sensitive to Infrared (heat-) radiation. This means that it can look further out into the Universe than with any other telescope and see the first galaxies as they form. Check also the pages on NGST.
9. Q: As the Big Bang could be similar to a conventional blast, and therefore the Universe developed around it, how is possible to state that there is not a center of the universe? And then how is possible to take a picture of the most ancient radiation and see it as it were around the photographer(Hubble and then us)?
A: The similarity of the expansion of the Universe to a conventional blast is a typical misconception in the popularizations of the cosmological model, possibly due to the unfortunate choice of the name 'Big Bang'. As a matter of fact 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 the space-time 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. An additional difficulty, that is related to your second question, is due to the fact that the velocity of light, although very high, is still finite (~ 300 000 kms-1). 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 image of the surface of the Sun that we can observe is always 8 minutes old, because it takes about 8 minutes for the sunlight to reach the Earth. If you look at the stars of the Orion constellation, which are roughly at a distance of 900-1000 light years, you see them as they were 900-1000 years ago. If some of them would have exploded today as a supernova, you (or your future relatives!) would know about this event only in a millennium.
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. We see 'Universe' around us up the limit that cosmologists call the 'horizon'. As time passes by we see more and more Universe, as the horizon gets bigger and bigger. This scenario must be true for any 'observer' in the Universe and he or she will think to be at the 'centre' of the expansion. In this sense there is no centre. Your questions are very profound because they go back to the very nature of space-time and of the cosmological models. It is not easy to answer properly in a few sentences. We would suggest you take the time to read some serious scientific book on Cosmology and meditate on the difference between the 'world' that we model around us on the basis of our daily experience and the one that describes the entire Universe. The difference in scale matters a lot !
10. Q: I was wondering a few things. First how far can the Hubble Space Telescope actually see.?
A: Actually the telescope itself poses no limits - but the Universe itself does. Hubble is a medium-sized (2.4 meter) telescope with very sharp optics and very good instruments. This enables the telescope to see very faint objects despite its relatively modest size. According to the theory of Big Bang the absolute observational limit to telescopes (as we know them today) is a 'sphere' of opaqueness surrounding us positioned approximately 13-14 billion light years away. It is called the 'surface of last scattering' and is also know as the source of the 'microwave background radiation'. Up to 300 000 years after Big Bang the Universe was totally opaque to light. This means that we know that we (when we look out in the Universe and thus back in time) will never see past, or through, this barrier.
Today galaxies have been seen with Hubble that are at a distance of approximately 12-13 billion light years. In the coming years more distant galaxies will undoubtedly be detected, but the limit for our observations will not move a lot for two reasons. Firstly the galaxies have to have time to form stars after Big Bang (this takes roughly one billion years). Secondly the young galaxies will be enshrouded in large amounts of dust that will - at least to some degree - obscure our view of the early Universe.
11. Q: What if the hubble teleskop would watch the Earth, what resolutions would the images possible have? I would guess approx. 10 - 20 cm?!?
A: Hubble's so-called angular resolution - or sharpness - is measured as the smallest angle on the sky that it can 'resolve' (i.e. see sharply). This is 1/10 of an arc-second (one degree is 3600 arc-seconds). If Hubble looked at Earth - from its orbit of approx. 600 km - this would correspond to 0.3 meter or 30 cm (almost the same as you found). Quite impressive! Unfortunately Hubble will never be turned to Earth since a) the brightness of the Earth could be damaging for the telescope and the instruments, and b) there is not any particularly interesting astronomical research to be done there (the type of science that deals with the Earth is called geophysics).
12. Q: In the Hubble FAQ you mention that the telescope will never be aimed at the Earth. What about the Moon? Would it still be damaging for Hubble's instruments? If feasible, could these observations take a picture of the landing site of the Apollo missions?
A: Indeed there has been a few cases where Hubble has been aimed at the Moon - see here. It has to be done with greatest care (since the Moon is very bright and can damage instruments etc.), and is normally avoided. Even with Hubble's incredible sharpness (resolution) only objects the size of a football field can be seen (~100 metres)... So no Apollo spacecrafts will be visible.