If you’ve ever wanted to navigate the night sky, this post is for you! Today I’m sharing how to use a star chart. After reading this article (and with a little practice on your own), you should feel comfortable going out at night and finding your favorite constellations. So let’s get started!
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Step 1 // Choose the correct star chart.
What is a star chart? Simply put, a star chart is a map of the night sky, one in which the major stars and constellations are drawn out. A star chart can come in a few different forms. You can have an all-year planisphere that rotates for your specific day/time, a seasonal chart (Spring, Summer, Fall or Winter), or a monthly chart. I’ll be covering how to use these basic charts today! There are also other, more advanced star charts that give information such as ascension and declination of celestial object that I won’t be covering at this time.
Below is a picture of my Pocket Star Finder (planisphere) as well as a monthly sky chart for November I printed (free charts for both Northern and Southern hemispheres can be found HERE).
The most common star charts are planispheres (year-round) and monthly maps.
Because stars are so distant from us, their relative locations between each other seem to remain constant from our perspective on Earth. You can think of it as the stars being on a celestial sphere or globe, and from our perspective on a point inside the globe, the stellar background rotates around us. (In reality, we are the ones rotating with the (relatively) constant stellar background.) This concept is important to remember because it means that with this rotation, the sky will look different depending on your location on Earth, as well as what season you are in. But it also means that we can record this celestial background onto a map and then use this map to find stars and constellations time and time again. (The stars won’t randomly reconfigure each time we look up into the sky!)
Thus because of this time and location dependence, when choosing the right sky chart, make sure you are either using an all-year planisphere or one that is applicable to your given season/time of the year. Also make sure that the chart is applicable for your given latitude. Star charts will generally give a range of latitudes over which they can be used. Most “Northern Hemisphere” star charts can be used for the majority of the U.S. Below is a picture of the latitudes over which this star chart is applicable. Most star charts will print the latitudes, dates, and times over which they are representative.
Make sure your star chart is applicable to your location (latitude) and time (date, time of day).
For the monthly sky charts, you are good-to-go and can move on to the next step! For the year-round planispheres, you will need to make sure to rotate the map to the correct day and time. For instance on the chart below, I have rotated it to align for November 10th at 9pm. That means that the stars I see in the window will be the ones visible at this given date/time.
Tip: Note also that many star charts do not account for Daylight Savings Time. So you will need to subtract one hour if you are in Daylight Savings Time.
Align the correct date and time of your planisphere.
And now you are ready to start orienting yourself (and your map) with the night sky above you!
Tip: While each star chart is different, most all can be read using the directions I’ve outlined here. If you would like additional help on how to use your specific star chart, each will usually have directions printed somewhere on the map. For my hand-held one, the directions are located on the back. For this printable version, the directions are around the outside of the circle.
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Step 2 // Orient yourself.
Because the sky and stars are above you, a star chart is read by holding it above your head. As with any map, it is directional and so it is important to know which way is North-South-East-West. If you don’t have a compass with you, you can also use the North Star to guide you. (see below)
Finding North: You can use the Big Dipper to find Polaris, the North Star, which always points Northward. Once you’ve found the Big Dipper, locate the outer two stars of its bowl and follow them out of the bowl toward the North Star, which should be brighter than those stars around it. Once you’ve found the North Star, you know you are facing North. Directly behind you is South, to your right is East, and to your left is West. More information HERE.
Okay! So now you know which way is North and South and can orient the map correctly. You can face whichever direction pleases you, but I generally start out by facing south (North Star to my back). Once I am facing South, I hold the star chart outward, with the “Southern Horizon” at my feet. (See the picture below.) The stars at the bottom of the chart would be at the horizon directly in front of me. The stars in the center of the chart would be directly above me (zenith). And the stars at the top of the chart, under “Northern Horizon” would be directly behind me. You can rotate your arm upwards so that the star chart is above your head if it is easier to visualize for you.
Again, you can face whichever direction you’d like, just make sure that the direction you are facing is the direction of the map held at your feet. It’s helpful to also remember that the edges of the map represent your horizons, while the center of the map represents the sky space directly above you. The steps in the section are the same for the planisphere as they are for the monthly sky charts.
Facing South, the southern direction of the star chart should be at your feet.
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Step 3 // Start with what you know.
When starting out, look for constellations you know–like the Big Dipper and Orion. Try to align them on the map and orient yourself to the night sky.
image, Big Dipper and Little Dipper.
Tip: If you are having trouble finding a particular constellations, start out with the brightest stars of the group, which will generally appear as larger dots on the star map. (see picture below) Once you locate the brightest stars, you can fill in where the others should likely be. Depending on where you are, light pollution from a nearby city may be blocking the light from the faintest stars. Also a fun/confusing note of clarification, brighter stars will have a lower magnitude. Just a funny artifact of how astronomers have always designated them. So in the picture below, the brightest stars (biggest dots) will have magnitudes of -1, while the faintest stars (smallest dots) will have magnitudes of 4.
After you find constellations you know, move on to new ones you don’t know! And be patient finding new stars and constellations–it can take some time to see them!
Tip: Also, do not use a normal flash light when using a star chart at night. The light from a flash light will desensitize your eyes to the night sky, and make finding stars harder. Each time you use the flash light you will have to give your eyes time to readjust to the dimness of night. Instead use a red flash light or place a red filter over a normal flash light to save your night vision. (I use my camping head lamp that has a night vision setting.)
After enough practice, you may start to notice that some stars have different colors. Hotter stars will appear blue and white, while cooler stars will appear yellow, orange, and red.
You may also notice other objects, like galaxies, nebulas, and star clusters denoted on your star chart. These are generally too faint to see with the naked eye, but if you have a telescope or even binoculars, many of these objects can be seen! Try to find these as an added challenge after you’ve mastered the constellations.
Star charts will generally denote brighter stars with larger dots. Sometimes galaxies, nebulas, and star clusters are also illustrated.
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Step 4 // Try to find planets along the ecliptic.
If you notice a particularly bright object that you can’t locate on the star chart, you might have found a planet! Planets will move along the ecliptic plane, usually denoted as a dashed line running through the sky map (highlighted in yellow in picture below). The ecliptic plane is the plane in which the Earth, Moon, and all the planets rotate about the Sun.
Planets can be found along the ecliptic plane, highlighted in yellow above.
If the planet is extremely bright and white, and near the sunrise or sunset horizon, it is most likely Venus. If the planet is similarly white but a little less bright, it may be Jupiter. (If you’ve got a good telescope, you can even see the moons around Jupiter! One of my favorite things of all time to look at.) Mars will appear to be a deep red color, while Saturn will be a yellowish-white color. Mercury is rarer to find, but can occasionally be found brightly flashing near the western horizon at sunset or the eastern horizon at sunrise. And don’t forget about the Moon, which can be spectacular to look at (and easy to find!).
image, The Moon and Mars.
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Step 5 // Explore the night sky!
And that’s all there is! You now have all the tools you need to use a star chart successfully and to explore the night sky. Viewing the night sky and learning the constellations is one of those ancient skills that many humans don’t possess anymore but one that will connect you with our species through space and time.
image, Venus and Jupiter.
And while it definitely takes practice to make perfect, it’s a skill you will be so happy you have. And don’t forget that you’ll see different constellations each season, for a year full of new sights and discoveries. Challenge yourself and have fun exploring the Cosmos tonight, friends!