Welcome to the Night Sky Map for August 2021! This month, we talk about one of the night sky’s most magnificent sights—the summer Milky Way, which is the galaxy in which our Sun and all of its planets are located. Here’s how to see the Milky Way in the summer night sky.
Just click here or on the image below to open the printable map—then bring outside!
The Milky Way Galaxy
Late summer is one of the best times of year to view the full splendor of our galaxy, the Milky Way.
From our vantage point within the galaxy, the Milky Way appears as a huge, shimmering cloud of light arching from the southern horizon to high overhead. It glows with the combined light of billions upon billions of faraway stars, each too faint for our eyes to resolve. Added together, these myriad stars produced the soft glow that we see as the Milky Way.
While the Milky Way appears as an arch to our eyes, it is actually a spiral galaxy—a sprawling pinwheel of starlight and dust containing 100 to 400 billion stars! Specifically, it’s a “barred spiral galaxy” because it has a central bar bar-shaped structure composed of stars. This is not uncommon. The current hypothesis is that the bar structure acts as a type of stellar nursery, fueling star birth at their centers.
Imagine a disk with spiral arms reaching out from the center. Within this huge spiral structure, Earth and the Sun and its planets are located in one of the spiral arms of the Milky Way (called the Orion Arm) which lies about two-thirds of the way out from the center of the Galaxy (and one third from the center of the galaxy).
Image showing where Earth resides within the Barred Spiral Milky Way. Credit: Bill Saxton NRAO, AUI, NSF; Robert Hurt NASA.
Viewing the Milky Way
The Milky Way used to be visible on every clear, moonless night, everywhere in the world.
Sadly, the increase in light pollution over the past century has turned the Milky Way from a common sight into one that many folks have never seen. In 1994, when the Northridge earthquake knocked out power (and therefore light) to Los Angeles, emergency centers received calls from concerned citizens who reported a “giant silvery cloud” hovering over the city. Was it dangerous? Not to worry: The city dwellers were merely seeing the Milky Way for the first time in their lives!
You need a dark location to observe the Milky Way in all its glory. A typical suburban neighborhood won’t be sufficiently dark. Moonlight, security lights, and streetlights are enough to spoil the view. Look for a night when the Moon is young or it’s a New Moon. See your Moon phase tonight.
Seeing the Milky Way requires a special effort for most people, but it’s well worthwhile. The clearest skies appear just after a cold front passes through. Remember that your eyes need about 20 minutes to adjust to the dark.
From a properly dark, moonless viewing site, you can see the huge, hazy band of the Milky Way and maybe even the Great Rift, a large, dark strip of cosmic dust and gas that hides part of the Milky Way and appears to divide it in two, as shown on this month’s Sky Map below.
Note: Do not expect to see the Milky Way as you do in photographs that you see online. A camera can capture light better than our human eyes. What you may see is a whitish, cloudy—dare we say, milky—arc sretching across the night sky from South to Northeast. In the late summer, the brigher areas are in the southern part of the sky, toward the core of the galaxy, where the stars are more dense. Now look north, towards the outer edge of the Milky Way; the stars are less dense.
Unlike a meteors shower or other event, the Milky Way is on display every night of the year, and it’s especially grand in late summer. Find yourself to a really dark spot and check it out!
Enlarge this Map! Click here or on map below to open a large image.
Sky map produced using Chris Marriott’s Skymap Pro
The Perseid Meteor Shower
Another highlight in August is the Perseid Meteor Shower to our skies. The Perseids are one of the best meteor showers of the year, and they reach their peak on the night of August 12–13.
Known as shooting stars, meteors appear as brief streaks of light when small space rocks called meteoroids plunge into Earth’s atmosphere. Friction with the atmosphere heats the meteoroids to the point where they burn up, each creating a bright flash that we call a meteor.
Most meteoroids are no larger than grains of sand, but occasionally pieces of a big one survive the fi ery trip through the atmosphere to reach the ground. These surviving fragments are known as meteorites.
In summary, when moving through space, a tiny rock is a meteoroid. When we see it burn up in Earth’s atmosphere, it’s a meteor. If any part of the object survives its passage through the atmosphere and reaches the ground, it’s a meteorite.
Several times a year, Earth passes through streams of cosmic debris. When this happens, we may be treated to a meteor shower in which the number of meteors jumps dramatically to anywhere from 10 to 100 meteors per hour.
In the case of the annual Perseid Meteor Shower, every August, Earth encounters debris left behind by Comet Swift-Tuttle, which was discovered in 1862. As Earth plows through the cometary debris, each little particle appears in the sky as a momentary streak of light—a meteor.
Perseid meteors can appear anywhere in the sky, so your best viewing strategy is to recline or lie on the ground and look toward the darkest and most unobstructed region of the sky. A sleeping bag or air mattress makes meteor watching a lot more comfortable.
Note: How to Read the Sky Map
Our monthly sky map does not show the entire sky which would be almost impossible. Instead, the map focuses on a particular region of the sky each month where something interesting is happening. The legend on the map always tells you which direction you should facing, based on midnight viewing. For example, if the map legend says “Looking Southeast,” you should face southeast when using the map.
The map is accurate for any location at a so-called “mid northern” latitude. That includes anywhere in the 48 U.S. states, southern Canada, central and southern Europe, central Asia, and Japan. If you are located substantially north of these areas, objects on our map will appear lower in your sky, and some objects near the horizon will not be visible at all. If you are substantially south of these areas, everything on our map will appear higher in your sky.
The items labeled in green on the sky map are known as asterisms. These are distinctive star patterns that lie within constellations. When getting your bearings under the stars, it’s often easiest to spot an asterism and use it as a guide to finding the parent constellation.
The numbers along the white “Your Horizon” curve at the bottom of the map are compass points, shown on degrees. As you turn your head from side to side, you will be looking in the compass direction indicated by those numbers. The horizon line is curved in order to preserve the geometry of objects in the sky. If we made the horizon line straight, the geometry of objects in the sky would be distorted.