# Light pollution ``` By /u/Bersonic ``` A hugely important factor in astrophotography is light pollution. When you look up at the sky from the middle of NYC you may only see a few of the brightest stars. Drive a few hours away and you will see thousands. While light pollution won’t make or break your chances at a successful image, it sure can make getting there a pain. *** **Measuring light pollution** *** Light pollution is quantified by a special system called the Bortle Scale. The Bortle Scale is a 9 point scale measuring the brightness of the sky at Zenith (90 degrees up.) Each of the 9 levels of the scale are assigned a color. White, red, light red, orange, yellow, green, blue, grey, and black. These “zones” are projected onto services like Google Earth to create a light pollution map. White zones correspond to a Bortle scale of 8-9. These zones are found in heavily populated areas like cities and large suburbs. Black zones are rare and are usually found in the middle of deserts or oceans. *** **Effects of light pollution** *** To get an idea of what the sky looks like in different zones, here is a nifty graphic: The biggest problem light pollution poses to astrophotos is color. If you are unlucky enough to be in a red or white zone, you will quickly realize that your images are coming out with either a orange or green tint. If you see this do not fret. Astrophotographers are a smart bunch, and have figured out a number of ways to remove light pollution “gradients” in post processing. The other problem light pollution creates is that it brightens an image considerably. this can create problems for people with fast scopes, or with people doing long exposures. After taking your first raw frame, check its histogram (most cameras will let you do that on camera.) If your main spike is in the left left 2/3 of the graph, then you are fine. Example: ----- /\ ---- is fine. If your main spike is close to the right wall of the graph, you need to back your exposure time down, lower your iso, or go to a darker site (go down a Bortle scale). *** **Light pollution map** *** To find out your closest dark sites, use this handy map: [Light pollution map](http://djlorenz.github.io/astronomy/lp2006/overlay/dark.html) --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://r-astrophotography.gitbook.io/r-astrophotography-wiki/light-pollution.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.