# Quantifying The Effect Of Skyglow On The Visibility Of Stars

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Contents

## Introduction

In this experiment (Quantifying the Effect of Skyglow on the Visibility of Stars), we will see if the angle of observation and the distance of the site from the urban centre can predict the amount of skyglow.

## Basic Building Concept

1. Skyglow is the amount of diffuse light caused in the night sky, in which moonlight or starlight are not involved.

2. The skyglow blocks the visibility of stars and is a bigger problem for astronomical observations.

## Aim

To predict the amount of skyglow with the help of the angle of observation and the distance of the site from the urban centre.

## Requirements

1. A digital camera

2. A computer program for isolating skyglow pixels and star pixels from the images.

## Theory

1. Observing angle is the angle between the observer and the source, i.e., the angular distance between the observer and the source.

2. Here, the urban centre refers to the astronomical observatory centre. Image of Skyglow

## Procedure

Step 1: With the help of the digital camera, take several pictures in the same kind of weather and moonlight between September and March from the sites of San Diego.

Step 2: The distance between the sites and the urban centre must be 30, 45, 60, 74, 100, and 124 Km (kilometre) at an angle of 45०, 60०, 90० (zenith), 120०, and 135०.

Step 3: Download all the clicked pictures and convert them into BMP files.

Step 4: Develop a program that can remove CCD noise for isolating skyglow pixels and for removing star pixels from the pictures. This program must be developed in a way that it can also measure the average intensity of the pixels of skyglow, which is between 0 and 765, for each picture.

Step 5: Now, you have to graph, average, and compare the resulting intensities obtained from each site to known functions. This is done to find out the suitable mathematical equation related to the intensity of skyglow as a function of the distance of the site from the urban centre and the observation centre.

## Observations

We have observed that:

1. From the distance of the urban centre, the amount of skyglow decreases inversely.

2. The approximated distance is measured by the equation, S = 2.4 X 10^2 X d^(-19) per one degree of the sky. Where d is the distance of the urban centre.

3. For non-zenith angles, skyglow is greater whether it is toward or away from the centre.

By applying the formula, we find out that.

4. The visible light coming out from the stars remain below 50% until the distance of 115 kilometres from the urban centre and increases up to 90% over this distance.

5. This indicates the increasing danger at the astronomical observatory near Palomar and Mt. Laguna observation centre.

## Result

1. The average intensity of the zenith pictures is different at all six sites. Which is 32.4 at 30km, 13.6 at 45km, 7.1 at 60 km, 5.8 at 75 km, 3.9 at 100 km, and 3.1 at 124 km from the urban centre.

2. We have derived an equation for the zenith pictures’ skyglow value, which is S = 2.4 X 10^2 X d^(-19) per one degree of the sky.

3. The skyglow amount measured at 45० to 60० angle of observation is 220% more than values of zenith skyglow for the same distance, and at 120० to 135० increases up to 87%.

## Precautions

1. Measure the distance correctly.

2. Check whether the program is working properly.

3. Make sure that the formula has been applied correctly.

## Conclusion

In this way, this experiment has helped us in quantifying the effect of Skyglow on the visibility of Stars, and we have also derived a formula for the skyglow.

Q.1 What was the aim of our experiment?

ANS. To predict the amount of skyglow with the help of the angle of observation and the distance of the site from the urban centre.

Q.2 What do you understand about the term skyglow?

ANS. Skyglow is the amount of diffuse light caused in the night sky, in which moonlight or starlight are not involved.

Q.3 Does the skyglow block the starlight?

ANS. Yes, the sky is blocking the visibility of the star.

Q.4 Why does the skyglow is a threat to astronomical observation?

ANS. Because it blocks the starlight from reaching out to the observatory.

Q.5 What is the formula which you have derived for the skyglow?

ANS. S = 2.4 X 10^2 X d^(-19) per one degree of the sky. Where d is the distance of the urban centre.

Q.6 What are the intensities of zenith skyglow around each site?

ANS. The average intensity of the zenith pictures is different at all six sites. Which is 32.4 at 30km, 13.6 at 45km, 7.1 at 60 km, 5.8 at 75 km, 3.9 at 100 km, and 3.1 at 124 km from the urban centre.

Q.7 What do you understand by the term observing angle?

ANS. The observing angle is the angle between the observer and the source, i.e., the angular distance between the observer and the source.

Q.8 What do you understand by the term urban centra?

ANS. The urban centre refers to the astronomical observatory centre.