What is a planisphere? It is a map of the sky. But, it is a very special kind of map because it is also a type of mechanical computer that can calculate the position of objects in the sky for any date and time. I have an app on my smartphone that does that. Why would I want to use a planisphere? There are lots of reasons to use a planisphere instead of a smartphone or computer.

So, you have a telescope or a pair of binoculars and you want to get started in astronomy. One of your first questions will certainly be, “what are the best things for me to look at in my telescope?” Let me introduce you to the Messier catalog. It is essentially a Top-100 list of the most beautiful objects in the night sky. What the Messier catalog is and how it came to be is an interesting and ironic tale.

Take a moment to examine the front of the planisphere. Here, we will briefly cover each printed element and describe its use. Date and Time Start by examining the area around the perimeter of the chart. You will find the time printed for each hour of the day, with small arrows shown in-between marking the half-hours. This ‘clock dial’ serves two purposes. The primary purpose is to be used in setting the planisphere to display the portion of the sky that is above the horizon at a selected date and time.

The back of the Messier Observer’s Planisphere includes several tables and observing aids that will come in handy on the observing field. Here, we will briefly cover each printed element and describe its use. Messier Object Cheat Sheet Filling the lower half of the rear side of the planisphere you will find a large table divided into three rectangular boxes. This table lists all 110 of the objects in the Messier catalog, plus a few other notable deep sky objects.

The Celestial Coordinate System You are probably familiar with using latitude and longitude to identify locations on the earth. Astronomers use a similar coordinate system to refer to locations in the night sky. Right Ascension is the astronomical equivalent of longitude. Just as longitude describes how far east or west some place is from a fixed reference on the surface of the globe, right ascension describes how far east or west something appears on the celestial sphere.

For Use Between 30 - 60 Degrees North Latitude The Messier Observer’s Planisphere was designed for observers in the northern hemisphere between 30 degrees and 60 degrees of latitude. If you are using the planisphere at a location that is further north or south, it will not give an accurate representation of which stars are above or below the horizon at a given date and time. In fact, for observers located south of 30ºN, there will be some stars visible in the sky that are not even printed on the map!

Astronomical objects can be very difficult to see. That is because they are very dim. Unlike stars whose light is concentrated into a single bright point, galaxies and nebulae are extended objects whose faint light is spread across a wide area. As a result, an astronomer can have their telescope pointed directly at an object but still be unable to see it. There are some subtle tricks that can be used at the telescope to glimpse those faint fuzzies.

Watch this video to learn how to use the Messier Observer’s Planisphere