The Birr Telescope

h.gricer

Could somebody answer this question that has always puzzled me. The Birr Telescope seems to very restricted in the area of sky it can view. From what I've seen from photos it appears it can only move vertical (up and down) but is restricted from moving side to side. A powerful telescope isn't much use if it can't view a great area of sky particularly when viewing planets, unless the Birr Telescope is in line with the ecliptic or the constellations of the Zodiac, you might have to wait for decades for Neptune to pass by, particularly if you just missed it.
Regards
h.gricer

Alun

Yes, it does have a limited azimuthal movement by using the ropes that support the tube, about 1 hour in fact, but is limited by the walls that are either side of it.

Capt'n Midnight

Taking viewing restrictions to their logical conclusion you get this.


A 6 Meter telescope with a parabolic liquid mirror for half nothing.

Only problem is that it's limited to looking straight up.
https://en.wikipedia.org/wiki/Large_Zenith_Telescope

ps200306

h.gricer wrote: »

Could somebody answer this question that has always puzzled me. The Birr Telescope seems to very restricted in the area of sky it can view. From what I've seen from photos it appears it can only move vertical (up and down) but is restricted from moving side to side. A powerful telescope isn't much use if it can't view a great area of sky particularly when viewing planets, unless the Birr Telescope is in line with the ecliptic or the constellations of the Zodiac, you might have to wait for decades for Neptune to pass by, particularly if you just missed it.

I think you don't want it in line with the ecliptic, so that the sky rotation carries planets across the field of view (though I think the Earl was more interested in deep sky objects). The telescope is aligned north-south, so it looks along the meridian. Anything that crosses the meridian on a given night will be visible, and as mentioned the telescope can slew in azimuth enough to see half an hour in R.A. either side of culmination. So in principle from Birr it could see anything down to -37° declination at some time of year, but I presume that in practice the telescope didn't have a full 90° of rotation in altitude.

mickmackey1

h.gricer wrote: »

Could somebody answer this question that has always puzzled me. The Birr Telescope seems to very restricted in the area of sky it can view. From what I've seen from photos it appears it can only move vertical (up and down) but is restricted from moving side to side. A powerful telescope isn't much use if it can't view a great area of sky particularly when viewing planets, unless the Birr Telescope is in line with the ecliptic or the constellations of the Zodiac, you might have to wait for decades for Neptune to pass by, particularly if you just missed it.
Regards
h.gricer

The weight of the telescope was such that it required a large support structure, namely an extensive chainage system connected to 56 feet high walls. The walls also prevented buffeting by the winds. Anything less would have led to a loss of rigidity, and in a powerful telescope this unwanted motion would have proved fatal to the quality of observations.

In practice the telescope could view anything from 13 degrees above the horizon to the zenith, and even slightly beyond. And no you wouldn't have to wait decades for Neptune to pass by, it remains within the ecliptic and would have been visible every year when crossing the meridian.

Zubeneschamali

It was the worlds largest telescope for 70 years from 1845 to 1917, so it was quite a while before those limitations were solved.

h.gricer

Many thanks for all the replies, the worlds largest telescope for 70 years, now that is impressive, it's definitely on my bucket list and see the real thing...