This app is a planning tool for people who want to take pictures of the night sky. You do not need to be an astronomy expert to use it.

You start by entering a location anywhere on Earth. It does not have to be where you are right now. It does not have to be today either. When you enter a location the app will try to validate it using a geocoding tool. From that tool it will get a longitude and latitude and from those coordinates it will try to get the elevation and time zone. The app will remember the last 10 locations you entered. You can use the down arrow to access that list or just start typing something new. The location you enter does not have to be exact. The nearest town and state should work just fine.

If the choosen observing date is different than today's date there will be a yellow boarder around it. There is also a calculation performed on the selected date for moon rise and moon set. Those dates will have a red boarder when the observing date is more than a few days from the new moon. This is just an FYI.

In order to display images of the objects found you need to pick what object types you are interested in, a camera and a telescope. From your choice or camera and telescope the app figures out what the field of view would be. You can add and delete cameras and telescopes that you use. You may notice that the frame around your object's image may not look quite square. This effect is more pronounced near the poles. This happens because the map is a projection of the sky sort of like a map of the world. The frame is trying it's best to show you what will be included in your astro image.

In addition to the Cameras and Telescopes pages there is now a Systems page that allows you to compare telescope and camera combinations. Instructions on how to use it are on the page.

Once you have selected a camera and a telescope you will see a number of calculations beneath them.

• FOV() is the image size in degrees/minutes of the selected camera and telescope.
• Pix() is the angular image scale for each pixel of the selected camera and telescope.
• See() is an estimate of the astronomical seeing needed for the selected camera and telescope to not be over or under sampling.
• Ray() is the Rayleight Criterion which is an estimate of the minimum distance between two points where they are clearly discernible as separate.
• Exp() is the change in exposure time from the previous camera and telescope choice. It is based on the Etendue equation on page 50 of Charles Bracken's excellent book "The Deep-Sky Imaging Primer, Third Edition"

Choose the object types you want to work with. Your selection controls which objects appear in query results. Pick a category using the buttons, or select types one by one. You can also put in a major axis minimum size in minutes (if available for object). There is a slider next to the size entry that allows you to decide whether or not to include objects that have no size available. This will keep your list of objects from containing things to small for your camera and telescope selections.

There is a new Moon Angle field added in Release 1.10.1 that shows the angle in degrees between the object and the Moon at midnight. You can enter a number of degrees on the query page that will limit the objects returned to those greater than the given angle from the Moon's location at midnight.

When you click on the Binocular Icon you will be taken to a View of the object using the Aladin API. You can change cameras and telescopes to see how the field of view changes. You can rotate the image as well. There is a field to the right of the camera that can simulate cropping the image. By default it has a value of 1. If you change it to 0.75 you are cropping your image by 75%. I added that one because I wanted to see what percentage of pixels I might loose to make the same size image from different combinations of telescopes and cameras. Use Shift-Click to move the camera frame to a different location or even a different object. It will try to figure out what the object is and display it below the viewer. A right click will bring up an Aladin context dialog with a number of interesting options for you to try.

Note: Rather than Longitude and Latitude, which are used to locate points on Earth, Astronomical objects like galaxies and nebulae are located in the sky using coordinates called Right Ascension and Declination. RA and Dec locate things in the sky. This app list objects RA and Dec.

What you can see in the night sky depends on where you are on Earth and what time it is. This app helps answer a simple question:

“What objects will be high enough in the sky for good photos from this location?”

When taking astrophotography images, objects that are too close to the horizon are affected by haze, light pollution, and atmospheric distortion. Most astrophotographers prefer targets that are at least 25–40 degrees above the horizon. For long exposures it is advantageous to choose a target that will be in the sky as long as possible. So, choosing a target that will be near the location's zenith at midnight will give you the longest possible exposure.

The app lets you search for objects in three main ways:

• Midnight (Overhead) Search
  

  Finds objects near the point directly above you (your zenith) at midnight. By entering a number of degrees North/South and East/West you are defining a box of a certain hight and width centered on the locations zenith at midnight. Ideally, choose something like 7.5 degrees for East/West when defining your box. That will produce a box with a width of one hour centered on midnight. These objects will be in the best location for maximum image exposure times.

• Area Search
  

  Lets you search a specific rectangular region of the sky, regardless of your location.

• Object Query
  

  Queries the Simbad database for all objects matching the description. You may use the percent sign % as a wild card, but be careful with it because there is a limit to how many objects this query will return.

A word on Cookies
Before version 1.10.6 this application used cookies in order to function properly. But, nothing is or was used for tracking or for marketing. It now uses exclusively local storage because the lifespan of a cookie is so limited on certain devices that things like your Favorites would so be lost. That said, there is still a Download To CSV function at the bottom of both the Favorites and Results pages.

Acknowledgements:

• Location Service provide by Nominatim - An Open-source geocoding tool with OpenStreetMap data.
• Elevation Service provide by Open-Elevation - An Open-source alternative to the Google Elevation API.
• Object Data provide by Simbad - An astronomical database maintained by the Centre de Donnees astronomiques de Strasbourg (CDS), Observatoire de Strasbourg in France.
• Sloan Digital Sky Survey Data provided by TAPVizieR - A service of the Centre de Donnees astronomiques de Strasbourg (CDS), Observatoire de Strasbourg in France.
• Images provided by Aladin - An interactive sky atlas and visualization tool used by astronomers (and serious amateurs) to explore the night sky with real survey images and astronomical data layered on top. Another service of the Centre de Donnees astronomiques de Strasbourg (CDS), Observatoire de Strasbourg in France.

Finally, I would be remiss if I did not acknowledge the great help provided by OpenAI’s ChatGPT in figuring out how to access all the above resources and in dealing with the seemingly labyrinthine workings of AWS.

The goal of this app is simple: help you decide what is worth imaging from a given place and time before you set up your equipment.