For other uses, see Night sky (disambiguation).
The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight, starlight, and airglow, depending on location and timing. The aurora borealis and aurora australis light up the skies of the Arctic and Antarctic circles respectively. Occasionally, a large coronal mass ejection from the Sun or simply high levels of solar wind extend the phenomenon toward the equator.
The night sky and studies of it have a historical place in both ancient and modern cultures. In the past, for instance, farmers have used the state of the night sky as a calendar to determine when to plant crops. Many cultures have drawn constellations between stars in the sky, using them in association with legends and mythology about their deities.
The anciently developed belief of astrology is generally based on the belief that relationships between heavenly bodies influence or convey information about events on Earth. The scientific study of the night sky and bodies observed within it, meanwhile, takes place in the science of astronomy.
The visibility of celestial objects in the night sky is affected by light pollution. The presence of the Moon in the night sky has historically hindered astronomical observation by increasing the amount of ambient lighting. With the advent of artificial light sources, however, light pollution has been a growing problem for viewing the night sky. Special filters and modifications to light fixtures can help to alleviate this problem, but for the best seeing both professional and amateur optical astronomers seek viewing sites located far from major urban areas.
Main article: Sky brightness
The fact that the sky is not completely dark at night, even in the absence of moonlight and city lights, can be easily observed, since if the sky were absolutely dark, one would not be able to see the silhouette of an object against the sky.
The intensity of the sky varies greatly over the day and the primary cause differs as well. During daytime when the sun is above the horizon direct scattering of sunlight (Rayleigh scattering) is the overwhelmingly dominant source of light. In twilight, the period of time between sunset and sunrise, the situation is more complicated and a further differentiation is required. Twilight is divided in three segments according to how far the sun is below the horizon in segments of 6°.
After sunset the civil twilight sets in, and ends when the sun drops more than 6° below the horizon. This is followed by the nautical twilight, when the sun reaches heights of -6° and -12°, after which comes the astronomical twilight defined as the period from -12° to -18°. When the sun drops more than 18° below the horizon the sky generally attains its minimum brightness.
Several sources can be identified as the source of the intrinsic brightness of the sky, namely airglow, indirect scattering of sunlight, scattering of starlight, and artificial light pollution.
Depending on local sky cloud cover, pollution, humidity, and light pollution levels, the stars visible to the unaided naked eye appear as hundreds, thousands or tens of thousands of white pinpoints of light in an otherwise near black sky together with some feint nebulae or clouds of light . In ancient times the stars were often assumed to be equidistant on a dome above the earth because they are much too far away for stereopsis to offer any depth cues. Visible stars range in color from blue (hot) to red (cold), but with such small points of feint light, most look white because they stimulate the rod cells without triggering the cone cells. If it is particularly dark and a particularly faint celestial object is of interest, averted vision may be helpful.
The stars of the night sky cannot be counted unaided because they are so numerous and there is no way to track which have been counted and which have not. Further complicating the count, fainter stars may appear and disappear depending on exactly where the observer is looking. The result is an impression of an extraordinarily vast star field.
Because stargazing is best done from a dark place away from city lights, dark adaptation is important to achieve and maintain. It takes several minutes for eyes to adjust to the darkness necessary for seeing the most stars, and surroundings on the ground are hard to discern. A red flashlight (torch) can be used to illuminate star charts, telescope parts, and the like without undoing the dark adaptation. (See Purkinje effect).
There are no markings on the night sky, though there exist many sky maps to aid stargazers in identifying constellations and other celestial objects. Constellations are prominent because their stars tend to be brighter than other nearby stars in the sky. Different cultures have created different groupings of constellations based on differing interpretations of the more-or-less random patterns of dots in the sky. Constellations were identified without regard to distance to each star, but instead as if they were all dots on a dome.
Orion is among the most prominent and recognizable constellations. The Big Dipper (which has a wide variety of other names) is helpful for navigation in the northern hemisphere because it points to Polaris, the north star.
The pole stars are special because they are approximately in line with the Earth's axis of rotation so they appear to stay in one place while the other stars rotate around them through the course of a night (or a year).
Planets, named for the Greek word for "wanderer," process through the star field a little each day, executing loops with time scales dependent on the length of the planets year or orbital period around solar system. Planets, to the naked eye, appear as points of light in the sky with variable brightness. Planets shine due to sunlight reflecting or scattering from the planets surface or atmosphere. Thus the relative sun planet earth positions determine the planets brightness. With telescope or good binoculars the planets appear as discs demonstrating finite size and also show phases like Earth's moon and also may possess their own orbiting moons which occasionally cast shadow onto the host planet surface . Venus is the most prominent planet, often called the "morning star" or "evening star" because it is brighter than the stars and often the only "star" visible near sunrise or sunset depending on its location in its orbit. Mercury, Mars, Jupiter and Saturn are also visible to the naked eye.
Earth's Moon is a grey disc in the sky with cratering visible to the naked eye. It spans, depending on its exact location, 29-33 arcminutes - which is about the size of a thumbnail at arm's length, and is readily identified. Over 28 days, the moon goes through a full cycle of lunar phases. People can generally identify phases within a few days by looking at the moon. Unlike stars and most planets, the light reflected from the moon is bright enough to be seen during the day. (Venus can sometimes be seen even after sunrise.)
Some of the most spectacular moons come during the full moon phase near sunset or sunrise. The moon on the horizon benefits from the moon illusion which makes it appear larger. The light reflected from the moon traveling through the atmosphere also colors the moon orange and/or red.
Comets come to the night sky only rarely. Comets are illuminated by the sun, and their tails extend away from the sun. A comet with visible tail is quite unusual - a great comet appears about once a decade. They tend to be visible only shortly before sunrise or after sunset because those are the times they are close enough to the sun to show a tail.
Clouds obscure the view of other objects in the sky, though varying thicknesses of cloudcover have differing effects. A very thin cirrus cloud in front of the moon might produce a rainbow-colored ring around the moon. Stars and planets are too small or dim to take on this effect, and are instead only dimmed (often to the point of invisibility). Thicker cloudcover obscures celestial objects entirely, making the sky black or reflecting city lights back down. Clouds are often close enough to afford some depth perception, though they are hard to see without moonlight or light pollution.
On clear dark nights in unpolluted areas, when the moon is thin or below the horizon, a band of what looks like white dust, the Milky Way, can be seen.
Shortly after sunset and before sunrise, artificial satellites often look like stars—similar in brightness and size—but move relatively quickly. Those that fly in low Earth orbit cross the sky in a couple of minutes. Some satellites, including space debris, appear to blink or have a periodic fluctuation in brightness because they are rotating.
Meteors (commonly known as shooting stars) streak across the sky very infrequently. During a meteor shower, they may average one a minute at irregular intervals, but otherwise their appearance is a random surprise. The occasional meteor will make a bright, fleeting streak across the sky, and they can be very bright in comparison to the night sky.
Aircraft are also visible at night, distinguishable at a distance from other objects because their lights blink.
6 Ways to Explore the Nighttime Sky With Your Kids
By Jacquie Fisher
Published October 10, 2013
Are your kids curious about the night sky?
Do they stump you with questions like “How many stars are in the sky?” or “Why does the moon change?”
There are lots of fun ways your family can learn more about the night sky together, right from your own backyard or kitchen table.
In this article I’ll show you six easy ways to introduce your kids to astronomy and feed their fascination with space—no telescope required.
Why Explore the Night Sky?
Take a few minutes after dark tonight to step outside with your kids and look up.
Now, ask your children what they see.
Kids are naturally curious and the sky above us is full of amazing things that incite wonder: the stars, the moon, the planets and the vastness of it all.
Observe the sky several evenings in a row and your kids will notice that the sky looks different each night than it did the night before.
The moon may appear to be getting larger or smaller. The stars may seem brighter and more noticeable (or dimmer and harder to see). The sky itself may seem brighter or darker.
And, of course, they’ll wonder why.
Take advantage of this curiosity and introduce your kids to the wonders of the cosmos.
The night sky is full of wonders to explore with your family. Go outside and look up! Image source: iStockPhoto.
It’s easier than you may think to teach your kids about astronomy. You don’t need to invest hundreds of dollars in a telescope or know much about science yourself to have a great time exploring space together.
This video shows how one family learned about the night time sky together.
You’ll discover six fun ways—from books, to phone apps to even a tasty snack—to feed your kids’ fascination with the starry sky.
You Will Need
- 1 bag of mini-marshmallows
- White pencil or crayon
- Black construction paper
- Constellation diagrams (link included below)
- Moon chart (link included below)
- Books from the book list (many can be found at your local library)
- Apps for your phone (can be downloaded with links included below)
- Optional: binoculars or a telescope for outdoor viewing
Most of the activities take less than 15 minutes of prep time; some will need to be completed at night when the stars are out
30 minutes to 3 hours (depending on how many activities you choose to do)
- Most activities can be completed at home or in your backyard
- Optional visit to an observatory or planetarium—they can usually be found within an hour of most locations.
Here are six fun ways to learn about space with your kids. Choose one or two, or choose all six.
#1: Read About the Moon and Stars
Story time is a great way to introduce children to new topics or expand their current knowledge.
My kids always like to learn new words they can impress me with and reading together is one of the best ways to do this. Astronomy has a whole vocabulary of its own they can show off!
There are many wonderful books you can read together about the moon, stars and other things you see in the sky. Check some of these out next time you’re at the library or bookstore.
These books can answer a lot of your kids’ questions so you don’t have to. They’ll explain that a constellation is a group of stars that make an imaginary picture in the night sky. Kids will also learn that the moon doesn’t ‘change’ its shape, why some stars look brighter than others, and how a star shines.
Your children may beg for another trip to the library soon, to get more astronomy books!
#2: Create Your Own Constellations
After learning about the stories and pictures behind the constellations, surprise your kids with this fun (and yummy) project.
Make your own models of the constellations from toothpicks and marshmallows.
Step 1: Choose your favorite constellation. Your kids’ favorite may be one that they can easily see in the sky or a myth or animal they like. We chose Orion, the hunter. His belt of three stars in a row is simple to find from where we live.
Choose a constellation you like. Draw it on black paper.
Step 2: Draw the constellation on black paper using a white pencil or crayon. Use constellation pictures from the books you read or from a constellation web-site as a template.
Build a model of the constellation using marshmallows and toothpicks.
Step 3: Construct the constellation using mini-marshmallows for the stars and toothpicks for the imaginary connecting lines.
Marshmallow constellations—a fun and tasty way to learn about the stars.
This project is lots of yummy fun and it helps teach kids what to look for when they peer into the night sky at the actual stars.
#3: Track the Size of the Moon
Your family will love this activity as you head outside to search for the moon each night.
Print out a calendar page to use for this activity from Science NetLinks.
Print this calendar to keep track of the phases of the moon for a month. Image source: sciencenetlinks.com.
Each evening or early morning, go outside with your children and find the moon. Sometimes you can locate it by looking out the window, but it’s best to head outside.
Go outside and find the moon. Image source: iStockPhoto.
Draw the shape of the moon on the calendar square for that day. After a few days, they will notice that the shape of the moon is changing.
A ‘waxing’ moon is one that appears to be growing larger and a ‘waning’ moon is one that appears to be getting smaller.
Track the moon every night for a month to see every phase of the lunar cycle. Image source: sciencenetlinks.com
You can also track the moon’s phases using apps on your phone. Download Moon Phases for the iPhone and iPad apps or Moon Phases Lite for Android.
Tracking the moon for a month will illustrate and reinforce one entire lunar cycle, bringing a concept that may be hard to grasp a little closer to home.
#4: Head Outside and Locate Constellations
On a clear evening, spend some time outside looking at the stars together. It’s a fun activity to do after a hike or a picnic dinner and it’s just as fun to simply turn off the TV or computer and step outside for awhile—no planning required!
Go outside and watch the stars come out.
We’ve had the best luck with seeing constellations and even some viewable planets by heading to a local park and away from the streetlights.
If you’re lucky enough to live near a large state or national park, they are optimal places for viewing the stars, as they have limited light pollution coming from artificial lighting.
Some stars have names. Others are actually planets. Occasionally you can even see the international space station zooming past.
You can print a map of the stars in the sky where you live (to the nearest city).
Get a map of the sky wherever you live. Image Source: SkyMapOnline.net
For a mobile approach, these apps will help you identify the constellations you can see in the night sky above you, right from your phone.
Simply point your iPhone, iPad, or iPod at the sky to identify stars, constellations, planets, satellites, and more!
Try SkyView for iPhone, iPod or iPad.
With these apps, all you need to do is hold your phone up to the sky. Your phone or tablet’s camera will read the stars to identify the location of the sky above you. You’ll be able to see the constellations on the screen as you try tosearch for them in the sky directly above. It’s pretty cool.
Point your Android device at the sky and Star Chart will tell you exactly what you are looking at.
If you have an Android, you can use an app such as Star Chart.
Note: The sky map for your area will change with the seasons as the earth’s tilt shifts so make sure that you have the correct map for the current season or things will seem confusing. Sea & Sky has a complete list of constellations that can be viewed each month.
There are some wonderful celestial events that occur each year and many can be viewed with the naked eye. Kids will enjoy viewing the sky during these events:
For more information on using star maps and star wheels, see this video from Sky & Telescope.
#5: Visit a Planetarium or Observatory
Are your kids addicted to space yet? After reading about the moon and stars, tracking the lunar cycle, making models of the constellations, and going outside for some good old fashioned star gazing with a modern technological twist, they’re probably begging for a visit to your nearest planetarium or observatory.
Many cities have planetariums or observatories that are open for public viewings and shows.
Observatories are buildings that house very large and strong telescopes that allow people to view stars, galaxies and celestial bodies. Families will get a great introduction to the stars and planets by viewing them through high-powered telescopes.
Visit an observatory to see the stars up close through a powerful telescope. Image Source: Steve Jurvetson
We had a great time during our visit to a local observatory. The viewing included stars in other galaxies, three planets and some amazing constellations. Find an observatory near you.
Check the show schedule for your closest planetarium and find the one that’s best for your kids’ ages. Our local planetarium has a wonderful ‘Sesame Street’ showing for young kids.
#6: Add some ‘Twinkle’ to Your Room
If your kids are like mine, once you start to learn about space together, they won’t want to stop. Here are a few ways to bring the stars right into your children’s bedrooms.
Create glow-in-the-dark constellations for your kids’ rooms.
My kids loved creating glow-in-the-dark constellations using peel-and-stick star kits that can be found online. I would suggest that you make them on paper that can then be hung on the wall or ceiling of your child’s room. The light during the day energizes the stars so they’ll glow at night.
Fun toys that allow kids to explore the stars from their own bedrooms.
There are also several toys and projectors that will shine constellations on the ceiling of a dark room. They’re a fun way for your kids to explore constellations every night.
So read them a book about the stars as they’re going to bed. They’ll be able to see those very stars on their ceiling as they’re drifting off into pleasant dreams.
Some Final Thoughts…
We love to go outside and look up at the nighttime sky. It’s a great way to spend some quiet time together, away from all the distractions indoors. I hope your family has fun exploring space and learning more about astronomy, too.
What do you think? I’d love to hear about your astronomy adventures! Please leave us a message or photo of fun ways you’ve explored ‘galaxies far, far away’ so we can all travel to the ends of the universe together!
Images from iStockPhoto and flickr commons.
Tags: astronomy, astronomy book, constellation, cosmos, galaxy, jacquie fisher, kids astronomy, lunar cycle, moon phase, observatory, outdoor activity, planetarium, sky map, skyview, star chart, waning moon, waxing moon