How to Use a Planisphere

When you think of star and planet gazing technology, the first item that springs to mind is most likely a telescope. But, before you begin working with such a complex (and expensive) object, you should first try out a planisphere.

Planispheres are simple devices that can show you incredibly complex things. The night sky is full of incredible planets, stars, and objects. Depending on where you live, you might only sometimes catch a glimpse of the stars above you. 

If your environment is often very cloudy or polluted, you might rarely see the night sky. But when you do, we bet you want to know everything about it. A planisphere will be the perfect entry into understanding space. You don’t have to buy anything expensive to look at and understand the worlds above you. 

A telescope is an amazing piece of technology. But they can be expensive and difficult to use. Planispheres are a very affordable way of understanding the planets and objects above us.

If you already have a telescope and aren’t quite sure where to point it or what you’re looking at, a planisphere is also a necessary object. But what exactly is a planisphere? Read on for our in-depth explanation and guide to using a planisphere accurately. 

What is a Planisphere?

A planisphere is a type of moveable star chart. It is usually made up of two disks that rotate. It is a handheld analog device but it is also a computing device. The two disks are held together in the center with a pin. The disks then rotate around this pin. 

Planispheres plot out the location of the stars and the dates of the year. Then, the user can turn the disks to find out which stars will be visible in the sky on which dates. It is a simple tool to use. But an incredibly complex and impressive tool to devise and create. 

So, how exactly do you use a planisphere?

How to Use a Planisphere - Step by Step

1. Choose your date and time.

The first thing to do when using a planisphere is choose the date you want to look for. Try out your birthday first and any time you like.

2. Rotate the top disk.

Once you have chosen the date and time, rotate the top disk so that the marker is set to the date and time. 

3. Face north, south, east, west.

For the planisphere to give you the most accurate guidance, you need to be facing the right direction. So, if you want to see something in the south, you need to face south and rotate the planisphere so that its south side is also facing south.

Using a compass is the best idea for this. You might even have one on your phone or you can download some very accurate apps. You don’t have to use an analog compass.

4. Now compare.

Now that you’re all set, compare your planisphere to the night sky. Depending on how clear the sky is, you should be able to find what you’re looking for.

But, reading the star chart on a planisphere isn’t quite as simple as you might think. Read on for a guide to reading a star chart. 

How to Read a Star Chart

Although you might be able to easily turn and adjust your planisphere, reading what it shows you is another skill. It’s not quite so simple as turning the planisphere and then looking straight up. You need to take a few things into consideration. 

The most important factor to consider is that the sky is not shaped like the flat planisphere in your hands. The exact layout of your star chart will vary depending on the kind you have.

But there are a few things that will be consistent. One of them is the position of the horizon. The outer edge of the circular star chart represents the horizon. 

This might be a little confusing at first. But you should be able to orientate yourself. The easiest thing to do, once you have set the dial, is hold the planisphere above your head. This will help you to line up the sky chart and the actual sky a little better. 

You also need to be facing in the right direction. This might seem obvious but it’s easy to walk out of your back door and look straight up. You can, of course, turn your planisphere around.

But this depends on whether you’re using your planisphere to work out a constellation you have seen. Or if you’re using your planisphere to find a constellation.

If you have seen a constellation and want to use your planisphere to work out which constellations you’re looking at, then you will need to turn your planisphere around. 

If, for example, you want to find Orion’s Belt, then you need to orientate yourself (after you have set the correct date and time on your planisphere and worked out if it will actually be visible).

Whichever you’re doing, a compass (even a compass app) will help you a lot. 

What a Planisphere Will Show You

Planispheres are impressive devices as they can show you a great number of things that sit in the night sky. But they cannot show you everything. You might have been taught the planets of our solar system and maybe a few constellations.

But, unless you studied astronomy or space in great detail, then you might not know just how many stars, planets, and objects there are above our heads.

Most planispheres are pretty exhaustive. But there just isn’t room for everything. A standard planisphere will be able to show you constellations and the planets. And some may even show you other deep space objects. But not every planisphere will have this.

What you will see on your planisphere will also depend on which kind you buy. This is because not everyone’s view of the night sky is the same. The differences depend mostly on whether you are in the northern or southern hemisphere. But if you are on the equator, this is also an important factor to consider.

It’s important to buy the correct planisphere for where you are in the world. Some planispheres are designed to be used anywhere in the world. But these will be crowded and a little complicated.

So, it’s best to get a specific planisphere. That said, there’s nothing stopping you from buying multiple planispheres. If you have a great fascination with constellations and planets, then you will likely find it interesting to know what someone on the other side of the world to you is seeing. 

Types of Planispheres

Using a planisphere is simple. But there are some very important things to consider before you start using one. The most important factor is where you are in the world. Whether you are in the northern or southern hemisphere will entirely determine which constellations you will be able to see. 

As mentioned above, planispheres are distorted. But because of the sheer magnitude of our solar system, they cannot show everything. This means that there are different planispheres for different areas.

Most commonly, there are planispheres for the northern and southern hemispheres. These are going to be much more accurate than any planisphere that claims it can show you the entire solar system. 

Because of the way the Earth orbits and rotates, certain stars and planets are only visible at certain times of the year. Before discovering that the Earth rotates and orbits, many cultures believed that the constellations moved.

This added to many of the myths surrounding these constellations. For example, the constellation of Virgo is associated with birth and rejuvenation in the northern hemisphere as it is most visible in spring and summer.

In the southern hemisphere, Virgo is associated with harvest as it is most visible during the fall months.

So, what are the differences and what will the northern and southern hemispheres show you? 

An Important Thing to Remember

A planisphere is a kind of map. And, as with pretty much any map, it is subject to distortion. This is because it is a celestial sphere laid out on a flat surface. Just as when you look at a map of the world, you know it must be distorted as the Earth is not a flat surface with rectangular edges.

So, when you’re using a planisphere to help you spot a constellation, it might not be exactly where you expect it to be.

This is also an important thing to remember in general. Especially when you’re trying to conceptualize the solar system and all the stars within it.

Our galaxy is huge and has an incredible number of planets and stars. Planispheres are amazing devices. But they are also very simple devices. They can only do so much. 

But, that said, they are impressively accurate. They are created using an exhaustive knowledge of the solar system and mathematics. 

Northern Hemisphere Planispheres

Currently, there are four northern hemisphere planispheres. These were published by the David Chandler Company. The latitudes for the northern hemisphere planispheres are:

  • 20° to 30° north - This covers the southern states of the USA, Mexico, North Africa, North India, and South China.
  • 30° to 40° north - This covers the mid-southern states of the USA, southern Europe, the Middle East, Central China, and Japan.
  • 40° to 50° north - This covers the mid-northern states of the USA and central Europe.
  • 50° to 60° north - This covers Canada, the British Isles, Northern Europe, and Russia.   

As you can see from these planispheres, it can be difficult to provide an exact charting of the night sky. This is due to the movement of the planets, of the stars, and of our own Earth. Planispheres can only show the night sky in segments. So they are not only divided up into one whole planisphere for the northern hemisphere. 

The more specific the planisphere you can get, the better. A planisphere for your specific area will be much simpler. This will give you a better idea of the area you’re looking at. It will also be much easier to read. Planispheres are simple devices but they can be quite crowded if they show a large area of the sky. The stars and constellations will overlap and make it difficult to read and differentiate. 

So, if you think you will only be viewing the night sky as it sits above the US states, then you need only buy a planisphere that shows the sky about the US states. If you want to see how the night sky looks around the world, then we recommend getting a series of individual planispheres. Rather than one that tries to show you everything.

Southern Hemisphere Planispheres

Planispheres for the southern hemisphere will look pretty similar to planispheres for the northern hemisphere.

Southern hemisphere planispheres can be used anywhere in the world between the latitudes 30° and 65° south.

Equatorial Planispheres

Although not as commonly available, there are also planispheres designed for use at the equator. When we talk about the northern and southern hemispheres, the equator often seems to be missed out.

But, if you’re on the equator or just fascinated by the night sky, an equatorial planisphere is just the device to add to your growing collection of stargazing equipment.

Equatorial planispheres are designed to be used from latitudes at 30° north to 30° south. But they can also be used anywhere in the world. This will be tricky (and we did earlier say not to trust any planisphere that tells you it can show you every constellation anywhere in the world) but this is possible.

It will be quite difficult and might take you a while to figure it out. But, as we said before, it will be easier to buy individual planispheres.

Latitude Specific Planispheres

If you want an even more accurate depiction of the night sky, you can get planispheres that are specific to your location. So, if you don’t expect to be looking from anywhere other than your backyard, this might be a great idea. 

Latitude specific planispheres allow you to know exactly what is above you. But, you will of course need to find the coordinates for your home. This can be pretty easy and you can look this up online.

The latitude specific planisphere might not give you a view that will be exact for your house. But it should be able to get pretty close. 

Interchangeable Planispheres

Although they are usually a little more expensive than standard devices, you can buy interchangeable planispheres. These are planispheres that have top disks that can be removed and swapped out.

These can either be for the northern hemisphere, the southern hemisphere, or the equator. They can also be for specific latitudes. 

Messier Object Planispheres

Messier objects are a set of objects within space. There are 101 of these objects and they were recorded by Charles Messier (hence the name). 

Planispheres haven’t changed very much since they were first invented. They are very simple devices and have mostly been updated as more scientific information became available. This means that there are now several different types of planispheres available. 

These include the ones specific to hemispheres and the equator that are listed above. They also include planispheres that plot Messier objects.

These are a little more difficult to use as there are so many Messier objects. But they will definitely be a worthwhile addition to your stargazing device collection.

NASA Planispheres

There are several different types of planisphere but also several different companies that produce them. They might vary but not by very much.

One type of planisphere that you absolutely can trust are the NASA planispheres. These are called Kepler Star Wheels.

They aren’t quite as technical as the moveable devices you can buy. But they will give you the answers that you need if you want to find something out quickly. They can simply be printed off. 

Uses for a Planisphere

So, now you know exactly what a planisphere is and how best to use it, let’s go over why you should get yourself one. Here are just a few of the fascinating things a planisphere can be used for.

  1. Finding the Zenith. The Zenith is the constellation above your head right now. So, if you’re outside and looking at the night sky, wondering exactly what you’re looking at, you can simply take out your planisphere, set it to your date and time, and find out.

    This is fascinating enough for your own benefit. But it will be great to take with you if you go camping. Or if you’re just out in the garden with a few friends or having a party.

    Lots of people know of the constellations but few people know them by sight. But everyone is fascinated by the stars and constellations. So it will definitely be a hit.
  1. Find your astrological sign. Even if you don’t believe in astrology, it is still an objectively interesting idea. You probably know what your sign is but it is still worth checking on your planisphere.

    If you do believe in astrology and want to know exactly which constellation is your star sign and exactly the moment the sun will pass through it on your birthday, then you absolutely should buy a planisphere. 
  1. Planning future stargazing. Due to the nature of planispheres, you can also use them to work out when certain stars, constellations, and planets will be most visible. This means, for example, if you want to be able to see Virgo on your next camping trip, you can use a planisphere to decide the dates.

    It means you can be prepared for when your favorite constellations or planets will be most visible. So you will never miss a viewing again.

The History of the Planisphere

Planispheres are very old instruments. The word was originally used (in the Latin planisphaerium) to describe a spherical representation of the Earth on a map. In essence, a 2D representation of the 3D earth.

The word is recorded as being first used by Claudius Ptolemy in the 2nd Century CE. So, when you’re using your own planisphere, it might not be exactly the same as the original. But you are still using something with an incredibly long history. 

The first time the word “planisphere” was used in reference to a star chart was in 1624. This was by Jacob Bartsch, a German astronomer. Interestingly, Bartsch was the son-in-law of Johannes Kepler, who discovered Kepler’s laws of planetary motion.

Other Types of Star Charts

You have likely seen images of star charts before. They are usually rectangular maps in deep shades of blue with a circle in the center. Covering the map are the constellations and maybe the planets as well, depending on the chart.

But a planisphere is also a type of star chart. There are many different ways of plotting the stars and planets. Just as there are many ways of mapping the Earth. This is because it is impossible to accurately present something spherical on a flat surface. 

This means that there are multiple different versions of star charts and multiple different versions of planispheres. It is important to find one that is as accurate as possible. If you can, buy one from a well-known and reliable brand.

A company that specializes in stargazing equipment. Plotting the stars isn’t simply a case of drawing down what you see above your head. It involves complex mathematics.

Especially as you’re presenting something absolutely enormous, such as our solar system, on a piece of cardboard or plastic that is around 10 inches in diameter. 

Conclusion

So, there you have it. That is just about everything you need to know about planispheres. You may have come to this article with no idea what a planisphere was but now you are an expert.

Using a planisphere is easy. The most important thing to remember is to buy a reliable and accurate planisphere. But also to remember that no planisphere can give you a 100% accurate depiction of the night sky.

But, for now, this is about as close as you will likely get to the moon and stars. So it is absolutely worth trying out. 

Andy Morgan

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