Telescope Orientation Control in Space Quiz

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Questions and Answers

What is the formula for calculating the pixel scale of a telescope?

$\omega = \mu \times S$

What is the focal ratio of a telescope, and how is it represented?

The focal ratio is a lens or mirror's focal length divided by its aperture. It is represented as f/x, where x is the ratio.

How does the focal ratio of a telescope affect the brightness of a source?

The brightness of a source by telescope is proportional to the square of the focal ratio (F^2).

What is the angular resolving power (or resolution) of a telescope?

The angular resolving power (or resolution) of a telescope is the smallest angle between close objects that can be seen clearly to be separate. Signup and view all the answers

How is the telescope scale defined?

The telescope scale is defined as the focal length of the telescope. Signup and view all the answers

What is the purpose of the focal plane in a telescope?

The focal plane is where the image from the telescope's optics is focused. Signup and view all the answers

What does the amount of magnification in a telescope depend on?

The focal length of the eyepiece Signup and view all the answers

Describe the appearance of an Airy disk formed when plane wavefronts diffract upon encountering a circular aperture.

A bright central spot surrounded by rings of decreasing brightness Signup and view all the answers

What causes wavefront distortions in the atmosphere that produce interfering Airy patterns in telescope images?

Variations in refractive index Signup and view all the answers

How does turbulent motion in the atmosphere affect telescope images during a long exposure?

It moves the individual maxima around the image plane to produce a large seeing disk Signup and view all the answers

How is the Earth's atmosphere approximated when considering atmospheric refraction?

As a series of plane-parallel plates Signup and view all the answers

What is the effect of refraction in the Earth's atmosphere in the limit of a very large number of thin layers?

Curving the path of the incident ray Signup and view all the answers

What is the purpose of the correction plate in large anastigmatic telescopes?

To be located near the focal plane Signup and view all the answers

What design is popular for small telescopes to achieve anastigmatism?

Schmidt–Cassegrain Signup and view all the answers

What happens to off-axis images in the absence of other aberrations?

They fall on a spherical surface known as the Petzval surface Signup and view all the answers

What determines the radius of the Petzval sphere?

Curvatures and refractive indices of the mirrors and lenses Signup and view all the answers

Why does a flat detector placed tangent to the Petzval surface record most of its images out of focus?

Due to field curvature Signup and view all the answers

What solution can be implemented to address the blurring caused by field curvature for a large detector?

Bend the detector to match the Petzval surface Signup and view all the answers

What are the two methods mentioned for adjusting and stabilizing the orientation of a telescope in space?

Small rockets and spinning reaction wheels. Signup and view all the answers

How do reaction wheels work to change the telescope's orientation?

When the rotation speed of the reaction wheel is changed, the telescope begins to rotate in the opposite direction. Signup and view all the answers

What is a limitation of the prime focus configuration in a reflecting telescope?

It has some limitations, though the text does not specify what those limitations are. Signup and view all the answers

What is an advantage of the Newtonian telescope design?

It provides a more convenient access to the focus. Signup and view all the answers

What does a rocket require in order to produce a force on the telescope?

A supply of propellant. Signup and view all the answers

How does a compressed gas produce a force on the telescope?

Bursts of a compressed gas escape from a nozzle to produce a force on the telescope. Signup and view all the answers

In a Cassegrain telescope, what is the relation between the overall focal length and the sign (positive or negative) for a Cassegrain and Gregorian configuration?

The overall focal length, f, is positive for a Cassegrain and negative for a Gregorian. Signup and view all the answers

What are the two main aberrations suffered by classical Cassegrain and Gregorian telescopes?

Coma and astigmatism. Signup and view all the answers

How can both spherical aberration (SA) and coma be removed in a reflecting telescope?

By choosing the proper conic constants K1 and K2 for the primary and secondary mirrors. Signup and view all the answers

What is the name given to an aplanatic Cassegrain telescope with a hyperbolic primary and secondary mirror?

Ritchey–Chretien or R–C telescope. Signup and view all the answers

In the equations relating the parameters $\beta$, $m$, and $k$, what are the signs of these parameters for a Cassegrain configuration?

$\beta$ is positive, and $m$ and $k$ are both positive for a Cassegrain. Signup and view all the answers

What is the key difference between the tube length of a Cassegrain telescope compared to a Newtonian telescope of the same focal length?

The tube of the Cassegrain will be much shorter than a Newtonian of the same focal length. Signup and view all the answers

Study Notes

Basis of Telescopes

The amount of magnification in a telescope depends on the focal length of the eyepiece.
Telescopic images in the absence of an atmosphere are formed by plane wavefronts diffracting upon encountering a circular aperture, resulting in an Airy disk with a bright central spot surrounded by rings of decreasing brightness.
Astronomical seeing is image formation by a telescope in a turbulent atmosphere, where wavefront distortions caused by variations in refractive index produce interfering Airy patterns.

Atmospheric Refraction

The Earth's atmosphere can be approximated as a series of plane-parallel plates, with the surface as an infinite plane.
Refraction in the atmosphere curves the path of the incident ray, resulting in a seeing disk.

Telescope Mounts and Drives

Telescope mounts in space use small rockets or spinning reaction wheels to adjust and stabilize the orientation of the telescope.
Reaction wheels require an on-board motor and change the rotation speed of the wheel to rotate the telescope in the opposite direction.

Reflecting Telescope Optics

Prime Focus and Newtonian Telescope configurations have the advantage of simplicity and minimum light loss, but have limitations.
Cassegrain and Gregorian reflectors have different mirror configurations, with the Cassegrain having a shorter tube than a Newtonian of the same focal length.
The overall focal length, f, is positive for a Cassegrain and negative for a Gregorian.

Aplanatic Two-Mirror Telescopes

Classical Cassegrain and Gregorian telescopes suffer from coma and astigmatism, but an aplanatic telescope can be designed to remove these aberrations.
The aplanatic Cassegrain, or Ritchey-Chretien telescope, consists of a hyperbolic primary and hyperbolic secondary.

Telescope Scale and Pixel Scale

Telescope scale is the angular distance between two points on the sky, and is measured in arcseconds/mm.
Pixel scale is a measurement of how much of the sky is covered by one pixel, and is measured in arcseconds/pixel.

Focal Ratio

Focal ratio is a lens or mirror's focal length divided by its aperture.
Brightness of a source by telescope is proportional to F2, so a smaller focal ratio results in a brighter image.

Angular Resolving Power

The angular resolving power of a telescope is the smallest angle between close objects that can be seen clearly to be separate.
For large anastigmatic telescopes, the correction plate is usually located near the focal plane.

Monochromatic Aberrations

Off-axis aberrations, such as field curvature, cause images to fall on a spherical surface rather than a plane.
The radius of the Petzval sphere depends on the curvatures and refractive indices of the mirrors and lenses in the optical system.
A flat detector can produce blurred images due to field curvature, but bending the detector to match the Petzval surface can solve this problem.

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Description

Test your knowledge about controlling the orientation of telescopes in space, including methods like reaction wheels and small rockets. Understand how bursts of compressed gas and spinning reaction wheels affect the telescope's stability.