How to Read a Star Chart

In this video, we will review how to read a star chart. This really is a fundamental skill if you are interested in astronomy, whether you are a novice stargazer or an experienced observer. Before we begin, it is important to recognize that there are a variety of star charts out there. Reading star charts takes practice, so it can be challenging at first. Start with simple charts and gradually work your way up to more complex ones as you become familiar with the night sky. I will mostly focus on the maps released by the International Astronomical Union, the organization that defined the boundaries of the constellations that are used by astronomers today. When looking at a star map, the first thing you probably recognize are a series of dots with lines connecting them, and then these make shapes and patterns, and then these shapes and patterns have different names to them. And these are all constellations, and constellations are patterns of stars that appear to be grouped together, and they really are a human invention. The earliest origins date far back to prehistoric times, and cultures around the world really have adopted their own constellations. Remember, these patterns also change over time, but according to the International Astronomical Union, there are 88 designated constellations. Another thing you might notice when looking at this star map is the line that goes from one side to the other side of the map. This line is known as the ecliptic, and it is the apparent path of the sun, moon, and planets. The path of the sun has been recorded over thousands of years of human observation. If we zoom in here, any constellation that falls along the ecliptic is defined as a zodiacal constellation. Here's another version of a star map, and you can see this blue line right here, this is the ecliptic. So the sun passes through this constellation at some point during the year. Here's another view. These are the maps I will mostly use from the International Astronomical Union, and here you can see the ecliptic passing through Taurus. You may come across some maps that identify asterisms, such as this one. This is the Great Square of Pegasus, and here we have the Big Dipper inside the constellation of Ursa Major. These asterisms are false constellations. They are simple star patterns that are really useful when navigating the night sky. Their size and classifications can vary. For example, here is a picture of all the constellations, or the major ones that can be seen in this photo. But when you look at this through the lens of an asterism, you can see different things. For example, this is the winter hexagon, which connects the six brightest stars in this area of the sky. Here is the winter triangle, which has three different constellations, while this one has six different constellations. This is one that has a shape known as the sickle, and it's part of Leo the lion. So asterisms are really helpful to learn how to navigate the sky, and they really vary according to time, place, and culture. The next fundamental skill you need to have when reading a star map is learning celestial coordinates, such as right ascension and declination. As you're looking at this map, these are synonymous with lines of longitude and lines of latitude, but it has a different name since these are celestial coordinates. These names are known as right ascension, which measures the east-west coordinates, and declination, which measures the north-south coordinates. And like cities, every object in the sky has two numbers that fix its location, and this is the right ascension and declination. And these are a object's or a star's celestial coordinates. So let's break this down. We have right ascension. These are celestial coordinates that measure the east and west coordinates, and you can see I highlighted them here on the map. It's synonymous with longitude. Imagine the earth's latitude and longitude projected onto the night sky, and just giving it a different name. That's what right ascension and declination are. And in right ascension, we measure it in hours, minutes, and seconds. So here you can identify where that is on this map. Next is declination, and this measures the north-south coordinates. Here I traced it out right here, and we measure this in terms of degrees, arc minutes, and arc seconds. And like I said earlier, every star has a specific numbers that are designated, and those numbers are the right ascension and declination. Now let's review how to interpret the symbols on a star map. Keep in mind there can be a variety of symbols, but it's important just to read the legend on each star map so you know what each symbol represents. I'm going to use this top bar right here, but before we get into the objects, we're going to start with the stars. And a star is a bright ball of plasma held together by its own gravity. Nuclear fusion occurs within its core, and they emit electromagnetic energy. And stars on star maps often have two different types of representations. It can be a solid dot or a ring, and these are just different types of stars. A variable star is one that appears to change its brightness. For example, here is Orion, here is Betelgeuse, and it is a solid star, but it has a ring around it, and that is a variable star. You might also notice when looking at star maps that the size of the dots can vary, and this correlates with brightness or the magnitude of a star. And the bigger the dot, the brighter the star, but the number assigned to it is a little bit backwards. In fact, the brighter stars have a lower number designated to them. So I have a whole video explaining this. I'm going to leave the link below, but the important thing to know for a star map is the bigger the star, the brighter it is in the night sky. Some star maps will have Greek letters that are next to different stars throughout a constellation, and this designation is called the Bayer designation. And what it does is it involves assigning a Greek letter to each star within a constellation, and it's usually in order of apparent brightness. The brightest star is designated as the alpha star, the second brightest star is the beta star, and so on and so forth. Now keep in mind that this is just one type of star naming system, but this is the one that's commonly used. So if a star is known as the alpha star, like this would be Alpha Tauri, that is its Bayer designation, but then Aldebaran is its common name. When reading a star map, it is important to determine the orientation of the map. Some charts are designed for specific dates and times, while others are more general. Make sure you understand which direction represents north, south, east, and west on the chart. For this planisphere, each side represents a different direction. One side shows what the sky would look like when facing north, while the flip side represents what the sky would look like looking south. You can also turn this star wheel to specific dates and times to get a more accurate view of what the sky would look like at that date and time. This type of chart will not show you the movement of the planets, however, so you would need a different map source for that information. You can use websites such as SkyMaps.com to download maps for your specific location and month, or you can use an online planetarium such as Stellarium. Your star chart should match up with your specific location. When I observe from Hawaii, the star chart I use matches up with my latitude. Many star charts are specific to certain latitudes and times of the year. You can invest in a planisphere or a star wheel to take with you as a guide when you're outside at night stargazing. If you do this, I recommend using a red flashlight or some type of red filter to preserve your night vision while you're reading the chart in the dark. I made this red flashlight by just taking a normal white flashlight and painting it with red nail polish. It's possible you may come across maps that show the positions of the planet. You should also notice that these planets are often along the line of the ecliptic because this is the path of the sun, moon, and the planets. Many of these types of maps are really monthly maps because the position of the planets do change over time. They do not have a regular pattern like the background stars do. Planets are objects that orbit stars. They have enough gravity to be round and it's cleared out its orbital path of debris. And the planets that we can observe from Earth are the ones that are within our solar system. And the name planet is traced back to the ancient Greeks. They called them wandering stars because the pathway of the planets was really unique in comparison to the background stars. Sometimes they would seem to move faster in the sky and then slow down and then be inside a different constellation and then move fast again. So this was challenging and it's important that you understand that the planets will not always be in the same place on the star map. And when you're observing the planets in the sky, they do look different than stars. They're often brighter and we're not able to see all the ones that are located within our solar system. For example, this is a picture of Mercury and this right here is Venus. And in this picture you can see that the shape is more disc-like where this right here is a point of light and this is a star. And that's disc-like shape from our viewpoint is because it is so close. And the planets that are visible are Venus, Mars, Jupiter, Saturn, and Mercury. And keep in mind that their brightness can change over time. These, I do have a whole video about this topic so if you want to learn more about the motion of the planets, go ahead and see that video. Now we'll review the symbols of the celestial objects that you can see on a star map. And we'll start with the green ones right here. And those represent a type of nebula. And a nebula is a cloud of gas and dust. And they have their different categories. For example, the three up top don't really have a particular shape to them where the two at the bottom have a roughly spherical shape to them. And each of these, the three up here, these are areas of stellar birth where these these two down here are nebula that are at the end of their life. So I do have a whole video on the different types of nebulae that exist. But it's important to recognize that these are what their symbols represent. Now star clusters are the next celestial objects. And there's two types. Star clusters are groups of stars that are held together by gravity. And there's a globular cluster and an open star cluster. Open star clusters have this symbol and they don't really have a shape to them. They're kind of amorphous in what they look like. But a globular cluster has a roughly spherical shape. Of course, I do have a video on this. So if you want to learn more, go see that video. And there are common star clusters that are very recognizable. For example, the Pleiades star cluster is one that's visible to the naked eye as well as the Hyades star cluster. These are both open star clusters. So they don't have a regular shape to them where Messier 13, which is in Hercules, this is a globular star cluster. You can just see that its shape is different from this one. Now another celestial object you can identify on a star map is a galaxy. And this is the symbol for a galaxy. It's kind of like an oval and this one is colored in red. And a galaxy is a system of millions or billions of stars held together by the gravitational attraction between gas and dust. And there are different types of galaxies such as a spiral one, elliptical, and irregular. And of course, it's based upon shape. So that's how they are classified. And our Milky Way galaxy, I pointed out on a star map in an earlier part of the video, but when you look at it through the sky, this is a panoramic view of the night sky, you are looking at our own home Milky Way. And it's the combined light from all the stars in our home galaxy. We've come to the end of our video about how to read a star map. Please remember that reading star charts really takes practice and it can be challenging at first. Start with simple charts and gradually work your way up to more complex ones as you become familiar with the night sky. In order to help you develop your skill with reading a star map, I have included a stargazing starter guide for you. It includes more details about the night sky, constellations, celestial objects, and basic stargazing techniques. I also included both ancient and modern star charts for you to explore. To access this guide, click on the link in the comment and all you need is your email address to access it. Thank you so much for watching. Remember, keep going outside, bring a friend or pet with you, and as always, keep looking up.