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Two stars are \(3.7 \times 10^{11} \mathrm{m}\) apart and are equally distant from the earth. A telescope has an objective lens with a diameter of \(1.02 \mathrm{m}\) and just detects these stars as separate objects. Assume that light of wavelength 550 nm is being observed. Also assume that diffraction effects, rather than atmospheric turbulence, limit the resolving power of the telescope. Find the maximum distance that these stars could be from the earth.

Short Answer

Expert verified
The maximum distance that the stars could be from Earth is approximately \(5.63 \times 10^{17} \text{ m}\).

Step by step solution

01

Identify the Relevant Formula

To find the maximum distance from Earth that allows the telescope to resolve the stars as separate objects, we use the Rayleigh criterion for the minimum angular separation \( \theta \) given by the formula: \[ \theta = 1.22 \frac{\lambda}{D} \] where \( \lambda = 550 \times 10^{-9} \text{ m} \) is the wavelength of light and \( D = 1.02 \text{ m} \) is the diameter of the telescope's objective lens.
02

Calculate the Angular Separation

Substitute the given values into the Rayleigh criterion formula to calculate the minimum angular separation \( \theta \): \[ \theta = 1.22 \times \frac{550 \times 10^{-9}}{1.02} = 6.576 \times 10^{-7} \text{ radians} \] This \( \theta \) represents the smallest angular separation the telescope can resolve.
03

Relate Angular Separation to Physical Separation

Realize that the angular separation \( \theta \) is related to the physical separation \( x = 3.7 \times 10^{11} \text{ m} \) between the stars and their distance \( R \) from Earth through the small angle approximation: \[ \theta = \frac{x}{R} \] Rearrange to solve for \( R \): \[ R = \frac{x}{\theta} \]
04

Calculate Maximum Distance

Substitute the known values of \( x = 3.7 \times 10^{11} \text{ m} \) and \( \theta = 6.576 \times 10^{-7} \text{ radians} \) into the equation: \[ R = \frac{3.7 \times 10^{11}}{6.576 \times 10^{-7}} \approx 5.63 \times 10^{17} \text{ m} \] This results in the maximum distance the stars could be from the Earth while still being resolved as separate objects.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Telescope Resolving Power
The telescope resolving power refers to the ability of a telescope to clearly distinguish between two closely spaced objects as separate entities. This distinguishing capability is crucial in astronomical observations, particularly when viewing binary stars or distant celestial bodies. The resolving power is determined largely by the design and size of the telescope's objective lens or mirror.
One of the main factors affecting resolving power is diffraction, which causes incoming light beams to spread as they pass through the telescope aperture. This spreading can cause images of objects to blur together if they are particularly close, making it challenging to resolve them distinctly.
In practical terms, the resolving power of a telescope is quantified by the minimum angular separation it can distinguish. A smaller minimum angular separation indicates a higher resolving power, allowing finer detail to be observed. This quality is essential for astronomers aiming to study tightly clustered star formations, planetary details, or surface features on moons and nearby planets.
Angular Separation
Angular separation is an important concept in astronomy and describes the angle formed between two lines of sight extending from an observer to two distinct objects. This measure helps determine how close two objects appear in the sky.
Angular separation is typically measured in radians, degrees, or arcminutes, and it becomes especially relevant when discussing the resolution limits of a telescope. The smaller the angular separation, the more challenging it is to distinguish between the two objects without a high-resolving power telescope.
To resolve two stars clearly, they must have an angular separation greater than the telescope’s resolution limit, which is impacted by factors like aperture size and wavelength of the observed light. This concept is therefore intrinsic to the design and expectations we have for telescopic observations.
Diffraction Limit
The diffraction limit is the fundamental limit on the resolving power of an optical system due to the diffraction of light. When light passes through the aperture of a telescope, it doesn't just travel in a straight line. Instead, it spreads out, a phenomenon known as diffraction.
This spreading reduces the sharpness of the image and defines the smallest detail that can be distinguished by that telescope. The Rayleigh criterion, which many studies employ, uses this diffraction limit to determine the minimum angular separation that the telescope can resolve. It calculates the limit based on factors such as the wavelength of observed light and the diameter of the telescope’s objective lens or mirror.
Thus, the diffraction limit is a critical factor when astronomers and engineers design new telescopic systems, as overcoming it allows for improved image clarity and detail in celestial observations.
Wavelength of Light
The wavelength of light is a fundamental aspect influencing the resolving power of optical systems. It refers to the distance between consecutive peaks of a light wave and is typically measured in nanometers (nm) for visible light.
Different wavelengths interact uniquely with the optical components of a telescope, affecting both the diffraction limit and the overall resolution. A shorter wavelength allows for finer resolution, as it bends less when passing through the telescope aperture and hence leads to less diffraction spreading.
In the context of the exercise, the given wavelength of 550 nm is used to determine the smallest angular separation at which two stars can be resolved by the telescope. It thus plays an essential role in calculating the telescope's resolving power, directly influencing the maximum distance from which celestial objects can be clearly observed.

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Most popular questions from this chapter

In Young's experiment a mixture of orange light \((611 \mathrm{nm})\) and blue light \((471 \mathrm{nm})\) shines on the double slit. The centers of the first- order bright blue fringes lie at the outer edges of a screen that is located \(0.500 \mathrm{m}\) away from the slits. However, the first-order bright orange fringes fall off the screen. By how much and in which direction (toward or away from the slits) should the screen be moved so that the centers of the first-order bright orange fringes will just appear on the screen? It may be assumed that \(\theta\) is small, so that \(\sin \theta \approx \tan \theta\)

An Optical Monochromator. You and your team are designing a device that inputs a beam of white light (i.e., a continuous spectrum of visible light spanning all wavelengths from \(410 \mathrm{nm}\) to \(660 \mathrm{nm}\) ), and outputs a nearly monochromatic beam (i.e., a single color). Such a device is called an optical monochromator and is used in a wide variety of instruments and scientific experiments. In the instrument you are building, white light impinges upon the backside of a diffraction grating that has 1200 lines/cm. A movable rectangular aperture (a slit) is located on the opposite side of the grating, and can translate along a circular arc of radius \(20.0 \mathrm{cm},\) the center of which is located at the grating. (a) At what angle relative to the normal of the grating should the center of the slit be located in order to pass green light \((\lambda=550 \mathrm{nm})\) from first order \((m=1)\) diffracted light? (b) How wide should the slit be so that the wavelengths passing through the slit fall in the range \(540 \mathrm{nm} \leq \lambda \leq 560 \mathrm{nm} ?\)

In a single-slit diffraction pattern, the central fringe is 450 times as wide as the slit. The screen is 18000 times farther from the slit than the slit is wide. What is the ratio \(\lambda / W,\) where \(\lambda\) is the wavelength of the light shining through the slit and \(W\) is the width of the slit? Assume that the angle that locates a dark fringe on the screen is small, so that \(\sin \theta \approx \tan \theta\).

How many dark fringes will be produced on either side of the central maximum if light \((\lambda=651 \mathrm{nm})\) is incident on a single slit that is \(5.47 \times 10^{-6} \mathrm{m}\) wide?

A tank of gasoline \((n=1.40)\) is open to the air \((n=1.00) .\) A thin film of liquid floats on the gasoline and has a refractive index that is between 1.00 and \(1.40 .\) Light that has a wavelength of \(625 \mathrm{nm}\) (in vacuum) shines perpendicularly down through the air onto this film, and in this light the film looks bright due to constructive interference. The thickness of the film is \(242 \mathrm{nm}\) and is the minimum nonzero thickness for which constructive interference can occur. What is the refractive index of the film?

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