You just read a fashinating article of about Andromeda and you are eager to see it through your binoculars, but there is one problem. You don’t know where it is, right? You know where Orion and M42 are. You can locate the Pleiades as well as Venus, but you have no idea where are objects such as Betelgeuze, Altair, Vega and Arcturus. They are all there, up in the sky. You just need a chart in order to locate them. You need a star chart or a planisphere.

Hold on, what are the star chart and a planisphere? Let’s see how Wikipedia defines them.

“A star chart is a map of the night sky. Astronomers divide these into grids to easily use them. They are used to identify and locate astronomical objects such as stars, constellations and galaxies. They have been used for human navigation since time immemorial. A planisphere is a type of star chart. Note that a star chart differs from an astronomical catalog which is a listing or tabulation of astronomical objects for a particular purpose“. -Wikipedia 2007

Before we find out how to use a star chart or a planisphere, let’s talk a little about the background. Hippaskhos was the first one categorizing the stars based on their magnitudes. He defined six gategories in which the brightest stars belong to the first category and the stars you can hardly see belong to the last category. Usually the biggest dots in star charts indicate the category one stars, while the smallest dots indicate the category six stars. A star chart usually covers a smaller area of the sky while a planisphere covers the whole hemisphere. Because of this, star charts include more objects and can include objects of all six categories. The amount of objects you can see depends on the amount of surrounding artificial light and moon light, as well as sky conditions. The more pollution there is in the sky, the less astronomy objects you can see.

If you are interested to locate planets, star charts cannot provide much help. Planets are not marked in star charts because they keep on changing their locations. Anyhow, star charts include a dashed line, Elliptica, which is the rotation line of the Earth. All the planets can be found near the Elliptica.

There are 88 star clusters that have Latin names. All the clusters include one or more objects that are named like

“alpha” Lyr Vega

which indicates Vega at Lyra star cluster. Another example is

“beta” Lyr Sheliak

which indicates Sheliak at Lyra cluster  (WordPress content management software does not recognize alpha and beta characters, instead it chages them to a question mark. Because of this I must write them as “alpha” and “beta”).

The idea with naming is that the brightest stars are usually named with a lower case Greek letters or numbers. Next the genetive of a star cluster is added behind. For instance the brightest star Vega in Lyra star cluster is called as “alpha Lyrae”. Usually the name of the star cluster is shortened, such as “alpha Lyr”. In star charts the star clusters are drawn with connecting lines. The dashed lines in a star chart indicate that a star belongs to another star cluster as well.

So the star charts are a static representation of the nightsky. They help you to locate various star clusters as well as individual objects on the nightsky. The good thing with maps is that they provide more objects than a planisphere because they cover a smaller piece of the nightsky. You just need to pick up the right map for your viewing area. The downside is that you need quite a few maps for one year and one viewing area. A planishpere is a dynamic tool to locate the objects on a nightsky. Basically you set the current date as time into the planispehre by rotating it and then you put it above your head to see the map. The good thing with a planisphere is that you need only one planispehre which you can set to view the nightsky during different times of the year and day. The downside is that it is a rather small tool vocering a big viewing area. This means there are not many objects in a planispehre.

Now it is time for a quick wrap-up. I presented you the basic information on star charts and a planisphre which are tools used to locate objects on nightsky. Next time we will find out how you can use the star charts and a planisphere in order to locate your favourite objects.

Image source.