Single-dish radio telescope aperture

In summary, we discussed the construction of a new single-dish radio telescope called FAST, with a 500m aperture but only a 300m illuminated diameter. The advantage of the larger aperture is that it allows the feed system to be positioned over a range of locations while still capturing a 300m diameter of the dish. We also compared it to the Arecibo telescope, which uses a spherical reflector and a moveable feed horn, and discussed the difference in focus between the two designs. The angular resolution of a telescope is determined by the illuminated diameter, rather than the overall aperture size.
  • #1
shirin
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hello everyone!
this is a new single-dish radio telescope, FAST, under construction:
http://nextbigfuture.com/2011/06/chinas-five-hundred-meter-aperture.html
The aperture is 500 m. But the illuminated aperture is only 300m. So what is the advantage of bigger aperture?
is the angular resolution 1.22*wavelegth/300 or 500? if it is 300 so what is the preference of bigger aperture?
 
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  • #2
shirin said:
The aperture is 500 m. But the illuminated aperture is only 300m. So what is the advantage of bigger aperture?

Looking at the diagram and picture, I would say... The dish is 'fixed' (unmovable). The feed system above the dish moves to allow pointing at different locations. The 500m aperture size allows the feed system to be positioned/pointed over a range of locations while illuminating a 300m 'aperture' size of the dish area underneath.

How does that sound?
 
  • #3
Ok, thanks. Now I see it.
So is it correct to say that angular resolution of a telescope is dictated by the illuminated diameter not the aperture itself?
what about arecibo? Is the illuminated diameter of arecibo exact 300m or less? I read just now that it has a fixed dish and moving feed but smaller fov than that of FAST.
 
  • #4
shirin said:
Ok, thanks. Now I see it.
So is it correct to say that angular resolution of a telescope is dictated by the illuminated diameter not the aperture itself? what about arecibo? Is the illuminated diameter of arecibo exact 300m or less? I read just now that it has a fixed dish and moving feed but smaller fov than that of FAST.

The area of the surface used to illuminate the feed is most significant. In the case of FAST, it appears that the entire 500m dish exists to support the directionality, while only 300m diameter is captured by the feed horn (receiver). I couldn't find info to confirm for Arecibo, but I suspect it only uses a portion of its 300m diameter, too, being that the feed horns are designed to accept a specific signal 'cone' from the dish.

But there's more difference between FAST and Arecibo. Most radio telescopes use a parabolic surface that provide a crisp focus on distant objects at a single focal point. This works for moveable dishes that can be aimed. Arecibo uses a spherical reflector that introduces an error factor in focus, but it's the same in all directions and can be corrected for as the feed horn is moved to capture illumination from different targets. FAST, however, incorporates moveable panels that adjust to create a parabolic reflecting surface for different targets.

Here are the main wiki links:
http://en.wikipedia.org/wiki/Arecibo_radio_telescope
http://en.wikipedia.org/wiki/Five_hundred_meter_Aperture_Spherical_Telescope
 
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  • #5


Hello there! Thank you for sharing this information about the new single-dish radio telescope, FAST. The aperture of 500 m is certainly impressive and will allow for a larger collecting area for radio waves from space. The angular resolution of a telescope is determined by the ratio of the wavelength of the observed signal to the size of the aperture. In this case, the angular resolution would be 1.22*wavelegth/500, which means that the larger aperture will provide a better resolution. This is because a larger aperture allows for more precise measurements and a better ability to distinguish between different sources of radio waves. Additionally, a larger aperture also increases the sensitivity of the telescope, allowing for the detection of fainter signals. Overall, the bigger aperture of 500 m will greatly enhance the capabilities of this telescope and enable scientists to study the universe in more detail.
 

1. What is the purpose of a single-dish radio telescope aperture?

The aperture of a single-dish radio telescope is the opening through which radio waves are collected and focused onto a detector. The purpose of the aperture is to gather as much radio signal as possible from the source being observed, allowing for more sensitive and detailed measurements.

2. How does the aperture size of a single-dish radio telescope affect its performance?

The size of the aperture directly impacts the sensitivity and resolution of a single-dish radio telescope. A larger aperture can collect more radio waves, resulting in a higher signal-to-noise ratio and better sensitivity. It also allows for a higher resolution, meaning finer details can be observed.

3. Can the aperture of a single-dish radio telescope be changed or adjusted?

Yes, the aperture of a single-dish radio telescope can be changed by adjusting the size of the dish or by using specialized equipment to block or focus the radio waves. These adjustments can be made to optimize the telescope's performance for different types of observations.

4. How does the shape of the aperture affect the performance of a single-dish radio telescope?

The shape of the aperture also plays a role in the performance of a single-dish radio telescope. A parabolic shape is most commonly used as it allows for a more precise focusing of the radio waves onto the detector. Other shapes, such as spherical or elliptical, may be used for specific purposes or to correct for optical distortions.

5. Are there any limitations to the size of a single-dish radio telescope aperture?

Yes, there are limitations to the size of a single-dish radio telescope aperture. The size is limited by the practicality and cost of constructing and maintaining such a large dish. There are also physical limitations, such as the strength of materials and the effects of wind and gravity, that must be considered when designing and building a large aperture.

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