Bortle Scale Chart: 2024 Easy Guide for Amateur Astronomers

Are you tired of not being able to see the stars at night? Do you live in an area with bright city lights that make it impossible to stargaze? If so, you’re not alone. Many people struggle with light pollution, making seeing celestial objects in the night sky challenging. That’s where the Bortle Scale sky chart comes in.

The Bortle Scale is a handy numerical tool that allows for the measurement of the night sky’s brightness in a given location. With its nine distinct levels, this scale can accurately determine the extent to which you can observe celestial objects and the level of interference caused by light pollution. By providing this valuable information, the Bortle Scale enables us astronomers and stargazers alike to make informed decisions about where and when to observe the night sky, ensuring that we can fully appreciate the majesty of the universe in all its glory. 

In this article, you get

By the end of this article, you’ll know about the sky quality meter of the Bortle Scale and how to use it to find the best locations for exploring the night sky.

Let’s dive right in.

What Is the Bortle Scale Chart? Overview

The Bortle Scale Chart (or Bortle Scale Map) is a tool used to measure the night sky’s brightness at a particular location. It was created by John Bortle, an amateur astronomer, to help other amateur astronomers evaluate the darkness of the sky and the visibility of celestial objects.

The Bortle Scale Chart has nine levels, with Level 1 being the darkest and Level 9 being the brightest. The amount of light pollution in the sky and the visibility of celestial objects determines the levels. The lower the level, the darker the sky and the better the visibility of celestial objects.

If you’re an amateur astronomer like me, you can use the Bortle Scale Chart to help you observe the night sky. It is a valuable tool for planning observing sessions, choosing observing sites, and evaluating the quality of a particular observing site.

I describe the chart’s nine classes (levels) in each of the following sections.

Class 1: Excellent Dark-Sky Site

Class 1 is the darkest level of the Bortle Scale Chart. It is for the darkest and most pristine skies on Earth. Class 1 offers you the best possible views of the Milky Way. There will be no light pollution, and the sky will be incredibly dark.

The International Dark Sky Association has designated many Dark Sky Places in Class 1 zones, thanks to these spots having the darkest sky possible.

Read my articles on some of the best Dark Sky Places for exploring the night sky:

• Arizona dark sky sites, especially Sedona AZ
• Best places to see the Milky Way in California, especially Joshua Tree and Death Valley
• Colorado dark sky sites
• Florida dark sky sites
• Utah dark sky sites, especially Moab
• Texas skies are best in Big Bend National Park
• Hawaiian islands’ dark sky sites on Kauai, Oahu, and Maui

Class 2: Typical Truly Dark Site

Class 2 areas are also very dark but may have minor light pollution, such as a distant town or highway. The Milky Way is also clearly visible in Class 2. Class 2 is still an excellent location for observing the night sky. You’ll be able to see many of the same objects as Class 1, but the sky won’t be quite as dark. There may be some light pollution from nearby towns or cities, but it won’t be enough to impact your naked eye observations significantly.

Class 3: Rural Sky

Class 3 areas are rural or suburban. You’ll still be able to see many of the same objects as Class 1 and Class 2, but they may not be as bright or clear. The Milky Way is still visible, but it may be faint. Class 3 is still an excellent location for observing the night sky, but there will be light pollution from nearby sources such as street lights or buildings.

Class 4: Rural/Suburban Transition

Class 4 areas are transitional zones between rural and suburban areas. They have moderate light pollution from nearby towns or cities. In this class, you can see the Milky Way with some difficulty, and some deep sky objects like the Andromeda Galaxy are visible. However, light pollution from nearby cities may still be visible on the horizon.

Class 5: Suburban Sky

Class 5 is the Suburban Sky, with significant light pollution from street lights, buildings, and other artificial light sources. In this class, the Milky Way is no longer visible. Only the brightest stars and planets are visible.

Class 6: Bright Suburban Sky

Class 6 areas are bright with high light pollution from suburban street lights, buildings, and other sources. The sky is bright, and only the brightest stars are visible. In this class, the only celestial objects visible are the Moon, planets, and a few bright stars.

If you live in a class 4-6 location, there are still ways to enjoy stargazing. You can use a telescope or binoculars to observe bright objects like the Moon and planets. You can also find a darker location nearby, like a park or nature reserve, to escape the worst of the light pollution.

Class 7: Suburban/Urban Transition

Class 7 areas are transitional zones between suburban and urban areas. This class represents areas on the outskirts of urban or suburban areas. They have high levels of light pollution from many sources of artificial light. The sky is bright, and only a few stars are visible. While some dark areas may exist, the overall sky brightness is still relatively high. You may be able to see some of the brightest stars and planets, but fainter objects will be difficult to observe.

Class 8: City Sky

Class 8 areas are urban areas with very high levels of light pollution. The sky is very bright, and only the brightest planets and stars are visible. Class 8 represents areas that are within a city or town. The sky brightness is exceptionally high.

Class 9: Inner-City Sky

Class 9 areas are the brightest and most light-polluted areas on the Bortle Scale Chart. They are located in the heart of major cities and have incredibly high levels of light pollution. These areas are in the heart of a city or town, and the sky brightness is so high that only the Moon and a handful of the brightest stars are visible.

It may seem impossible to observe the night sky in these high Bortle Scale classes, like downtown Los Angeles, but you can still do some things to enjoy the night sky. Try stargazing early in the morning hours when fewer lights are on. You can also use a telescope or binoculars to observe the brightest objects in the sky, such as the Moon, planets, and bright stars.

In summary, the Bortle Scale Chart is a helpful tool for evaluating the darkness of the night sky. It helps amateur astronomers and stargazers like you and me choose the best observing locations and plan our sessions accordingly.

How to Use the Bortle Scale Chart

The Bortle Scale is a valuable tool that can help you determine the quality of the night sky and plan your observing sessions accordingly.

Benefits of Using the Bortle Scale

One of the most significant benefits of using the Bortle Scale is that it can help you find dark-sky locations. The lower the Bortle number, the darker the sky. For example, if you’re looking for a place to observe the Milky Way, you’ll want to find a location with a Bortle number of 3 or lower.

The Bortle Scale can also help you plan your observing sessions by showing what objects you can see. For example, if you’re in a location with a high Bortle number, you may not be able to see faint objects like galaxies or nebulae.

Limitations of the Bortle Scale

While the Bortle Scale is a helpful tool, it does have its limitations. For one, the Bortle Scale only measures the brightness of the night sky and doesn’t consider other factors like weather or atmospheric conditions to determine if it’s clear outside. Additionally, the Bortle Scale is subjective and can vary depending on who is making the observation.

You’ll need to find your location on a light pollution map. Once you have your location, look for the corresponding Bortle number by clicking on the light pollution level of your site. Use the Bortle number to determine the brightness of the night sky and plan your observing sessions accordingly.

Improving Light Pollution Awareness

Light pollution is a growing problem affecting our view of the stars, our health, and the environment. It’s caused by excessive artificial light, which can harm nocturnal animals and disrupt their natural behavior. As an amateur astronomer, you can help raise awareness about light pollution and its effects.

It’s vital to preserve dark skies for future generations. Reducing light pollution can improve our view of the stars, protect nocturnal animals, and reduce energy waste.

Bortle Scale in Amateur Astronomy

As an amateur astronomer, understanding the Bortle Scale is crucial in determining the best observing conditions for stargazing.

As an amateur astronomer, you should observe from a location with a lower Bortle Scale rating to get the best observing conditions.

Understanding the Bortle Scale is essential for amateur astronomers who want to observe the night sky. By using the scale to find a dark observing site, you can enjoy the beauty of the night sky and see more celestial objects.

Astrophotography

The quality of your astrophotography depends on many factors, including your equipment, your skills, and the conditions in your location. But by using the Bortle Scale to find the best site for your astrophotography, you can increase your chances of capturing stunning night sky images.

Frequently Asked Questions

what bortle is my sky?

Are you curious “What is the Bortle Scale for my location?” Determining the Bortle Scale class of your sky depends on your specific location. To find out the Bortle Scale class for your area, you can use the light pollution map website. Simply input your location, and it will provide you with the corresponding Bortle class when you click on the map, helping you assess the quality of your local night sky for stargazing.

Summary: Bortle Scale Chart

Thank you for reading my article “Bortle Scale Chart.” If you’re looking to stargaze, understanding the Bortle Light Pollution Scale is crucial. The Bortle map measures the sky’s brightness and helps you determine the quality of the night sky for stargazing. The lower the number, the darker the sky, and the better the stargazing experience.

To use the chart, start by finding your location’s Bortle Class ranking, which ranges from 1 to 9. Class 1 represents the darkest skies, while Class 9 indicates the most light-polluted skies. Once you know your location’s ranking, you can use the chart to identify what celestial objects you can observe at that location.

For example, if you’re at a Class 1 location, you can expect to see faint objects such as the Milky Way’s dust clouds and galaxies. At a Class 5 location, you can observe brighter objects such as the Andromeda Galaxy and the Orion Nebula. However, at a Class 9 location, you may only see the brightest stars and planets.

If you’re looking for a genuinely awe-inspiring stargazing experience, try to find a location with a low Bortle Class ranking. Using the Bortle Scale Chart can help you plan your stargazing trips and ensure the best possible experience. Remember, the darker the sky, the more celestial objects you’ll be able to see.