Archive for May 9, 2018

When youthful faith has fled

Posted in Poetry with tags , , , on May 9, 2018 by telescoper

When youthful faith has fled,
PU Of loving take thy leave;
Be constant to the dead –
PUThe dead cannot deceive.

Sweet modest flowers of spring,
PUHow fleet your balmy day!
And man’s brief year can bring
PUNo secondary May.

No earthly burst again
PUOf gladness out of gloom;
Fond hope and vision vain,
PUUngrateful to the tomb!

But ’tis an old belief,
PUThat on some solemn shore,
Beyond the sphere of grief,
PUDear friends will meet once more.

Beyond the sphere of time,
PUAnd sin, and fate’s control,
Serene in changeless prime
PUOf body and of soul.

That creed I fain would keep,
PUThat hope I’ll not forego;
Eternal be the sleep,
PUUnless to waken so.

by John Gibson Lockhart (1794-1854). The last three verses of this poem were adapted by Hubert Parry as No. 4 `There is an old belief’ in his Songs of Farewell.

 

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Celebrating the Sloan Telescope

Posted in The Universe and Stuff with tags , , , , , , , , on May 9, 2018 by telescoper

A little bird tweeted at me this morning that today is the 20th anniversary of first light through the Sloan Telescope (funded by the Alfred P. Sloan Foundation) which has, for the past two decades, been surveying as much of the sky as it can from its location in New Mexico (about 25% altogether): the Sloan Digital Sky Survey is now on its 14th data release.

Here’s a picture of the telescope:

For those of you who want the optical details, the Sloan Telescope is a 2.5-m f/5 modified Ritchey-Chrétien altitude-azimuth telescope located at Apache Point Observatory, in south east New Mexico (Latitude 32° 46′ 49.30″ N, Longitude 105° 49′ 13.50″ W, Elevation 2788m). A 1.08 m secondary mirror and two corrector lenses result in a 3° distortion-free field of view. The telescope is described in detail in a paper by Gunn et al. (2006).

A 2.5m telescope of modest size by the standards of modern astronomical research, but the real assets of the Sloan telescope is a giant mosaic camera, highly efficient instruments and a big investment in the software required to generate and curate the huge data sets it creates. A key feature of SDSS is that its data sets are publicly available and, as such, they have been used in countless studies by a huge fraction of the astronomical community.

The Sloan Digital Sky Survey’s original `legacy’ survey was basically a huge spectroscopic redshift survey, mapping the positions of galaxies and quasars in three dimensions to reveal the `cosmic web’ in unprecedented detail:

As it has been updated and modernised, the Sloan Telescope has been involved in a range of other surveys aimed at uncovering different aspects of the universe around us, including several programmes still ongoing.