The HubbleViews
-May, 23, 2005-
Astronomer Dr. Robert N. Tubbs, a discenting voice

Dr. Robert Tubbs, a discenting voice

"Perhaps I should emphasize that I don't want Hubble to be destroyed, I just wouldn't want the cost of servicing Hubble to cripple the rest of astronomy!

Perhaps it's best to start by summarizing what Hubble does and doesn't do.

Hubble does:

1. Produce the deepest visible-light astronomical images, deeper than any ground-based telescope. The Hubble deep fields have had a big impact on astronomy, both in terms of what you do see in these images, and also in terms of the objects which *cannot* be seen at visible wavelengths even in these deep fields.

2. Produce high resolution images which cover a wide field. No ground-based telescope can image such a wide field as Hubble with the same resolution that Hubble can achieve.

3. Improve the public opinion of astronomy and NASA (this is essential if NASA wants to prevent its budget from being cut)

The things that Hubble cannot do include:

1. Hubble cannot compete with ground-based telescopes in terms spectroscopy -- high resolution spectroscopy, integral field spectroscopy and deep infrared spectroscopy are all performed from ground-base telescopes, and are essential to astronomers

2. Hubble cannot produce images of bright objects with the high resolution which can be achieved from ground-based instruments (see e.g. MRAO Cambridge) Even slightly fainter objects can be imaged with the same resolution as Hubble at visible wavelengths from the ground (see e.g. Lucky Exposures).

3. Ground-based telescopes can now compete with Hubble in most types of infrared imaging -- this is why Hubble is now concentrating on the visible and ultraviolet.

Hubble is most often used to do follow-up observations of exciting new things which are discovered with other instruments (although when NASA releases the first Hubble images, the media sometimes incorrectly report that the objects were discovered by Hubble!). It is *very* difficult to obtain observing time on Hubble to look for objects which have not already been discovered by a different telescope.

However, the Hubble followup observations (with a wide field and relatively high resolution) are ideal for astronomers to get a good overview of a newly discovered object, and of course they make excellent posters for publicity material!
It is clear that the Hubble deep fields at visible wavelengths were of great importance to astronomy. It is worth remembering, however, that the faintest objects in these deep fields appear much brighter at near infrared wavelengths, where they can be imaged much more easily (e.g. note that the most distant objects in the original Hubble Deep Field (North) were found in infrared/submillimeter follow-up observations by ground-based telescopes, and are *too* *faint* to be seen in the Hubble image). This has driven much of the astronomical community towards doing infrared and submillimeter observations instead of visible-light observations, and it explains why the biggest new facilities in astronomy (ALMA, Spitzer space telescope, James Webb Space Telescope (JWST), Keck telescopes, VLT telescopes) are aimed at these wavelengths.

Of course astronomers would like to keep Hubble's visible-light view of the Universe *and* get the new infrared observatory (JWST), but with pressure on budgets this is looking less and less likely (for example, NASA HQ has already directed the JWST Project to study a descope of the 6.5 meter James Webb Space Telescope to a 4 meter telescope). The costs of a Hubble servicing mission would be so great that it *could* have a big impact on the money available for future astronomy projects such as these. So many astronomer are worried (myself included) that a call to "save the Hubble" will turn into something which will actually cripple the future of astronomy. It is certainly clear that future space telescopes such as JWST will be far, far more important than an extension to the life of Hubble, but that public opinion (motivated by campaigns such as "save the Hubble" may have a much bigger impact on NASA because of the way it is funded.

So perhaps we should also try to save the JWST from the budget cuts, or just call for "more money for space telescopes" in general. Ground-based imaging instruments such as ALMA may play an equally important role, but of course these are not directly effected by NASA budget cuts.

Anyway, that's my point of view!

Robert Tubbs


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