Hello stargazers! For the week starting July 21 to July the 27th, we’re focusing on the Milky Way Galaxy, and some of the prominent constellations and objects you can see along the galactic plane. We’ll also welcome this month’s Full Moon and discuss some of the visible planets this week. So, let’s get started!
Picture this: you're far from the city's glow, under a sky so clear and dark that it takes your breath away. Stretching across the cosmos is a band of light, so densely packed with stars that it looks like a river of glowing mist. That band of light is the Milky Way, our galactic home
Summer nights are perfect for viewing the Milky Way. This barred spiral galaxy stretches about 100,000 light-years across and contains between 100 and 400 billion stars. When you look up at the Milky Way on a clear night, you're seeing just a small fraction of our galaxy's immense population of stars, gas, and dust.
One of the most striking features of the Milky Way in the summer is the Galactic Center, located in the direction of the constellation Sagittarius. This area is home to a supermassive black hole known as Sagittarius A*, with a mass equivalent to about four million suns. While we can't see the black hole itself, the dense star fields and dark dust lanes that characterize this part of the sky make it an impressive region to observe.
The Milky Way’s structure is composed of several key parts: the central bulge, the disk, and the halo. The central bulge is a densely packed group of stars around the galactic center, containing some of the galaxy's oldest stars and star clusters. Surrounding the bulge is the disk, where most of the galaxy’s star formation occurs. The disk includes the spiral arms—regions rich in young, bright stars, nebulae, and star-forming areas.
In summer, from mid-northern latitudes, we can see the Milky Way’s bright core rising in the southeast and stretching across the sky to the northwest. You don’t need any special equipment to enjoy it, just look up! The spiral arms appear as bright, patchy regions of stars, especially visible in constellations like Cygnus, Aquila, and Scutum.
The halo is a spherical region surrounding the disk and bulge, containing older stars and globular clusters. The halo extends far beyond the visible galaxy and includes a large amount of dark matter, which influences the galaxy’s rotation and structure.
So, why is the Milky Way shaped like a flat disk? The answer lies in its formation and the laws of physics. When the Milky Way formed around 13.6 billion years ago, it began as a roughly spherical cloud of gas and dark matter. As this cloud collapsed under its own gravity, it began to spin. Conservation of angular momentum—a fundamental principle of physics—caused the collapsing cloud to spin faster as it contracted, much like a figure skater pulling in their arms to spin faster.
Over time, this spinning motion caused the gas and dust to flatten out into a rotating disk. This is because objects moving in a rotating system tend to settle into the plane of rotation. The stars we see in the Milky Way today formed within this disk, giving the galaxy its characteristic flat shape. The central bulge we observe is made up of stars that formed early in the galaxy's history before the disk fully developed, and the halo consists of older stars and globular clusters that didn't settle into the disk.
For those of you in areas with low light pollution, summer is an ideal time to observe the Milky Way’s spiral arms. One particularly interesting feature is the Great Rift or Dark Rift. This is a series of dark, obscuring dust clouds that block the light from the stars behind them, creating a dark lane running through the bright band of the Milky Way. The Great Rift is most prominent in the constellations of Cygnus and Aquila.
As you gaze at the Milky Way, think about our solar system’s position within it. We’re located about 27,000 light-years from the galactic center, in one of the spiral arms called the Orion Arm, or Local Spur. This vantage point offers us a unique view of both the inner and outer parts of our galaxy.
Then there’s the interstellar medium—the gas and dust that fill the space between stars. This material plays a crucial role in star formation and can create dark nebulae, visible as dark patches against the bright backdrop of the Milky Way.
Here’s another fun fact: the Milky Way is moving through space at about 600 kilometers per second! It’s part of a local group of galaxies, which includes Andromeda, the Large and Small Magellanic Clouds, and about 54 other smaller galaxies. Our galaxy and Andromeda are on a collision course and are expected to merge in about 4.5 billion years, creating a new galaxy sometimes referred to as "Milkdromeda."
The Milky Way has fascinated cultures around the world, each with its own stories and myths. From the "Silver River" in Chinese astronomy, to the "Pathway of Souls" in Native American lore, these stories reflect humanity's awe and curiosity about the night sky.
While summer is a great time to catch the Milky Way, it’s visible at different times throughout the year, depending on your location. The best views come from dark, remote locations on clear, moonless nights.
It's a reminder of how small we are in the grand scheme of things, but also of how much there is to explore and discover right from our own backyards.
Let’s take a tour through three constellations that lie along the Milky Way: Cygnus, Scorpius, and Sagittarius.
We’ve talked about Cygnus quite a bit in recent episodes. Known as the Swan, Cygnus is a prominent constellation in the summer sky, easily recognizable by its cross-like shape, with the bright star Deneb marking the tail of the swan. As part of the Milky Way, Cygnus is a rich hunting ground for deep-sky objects.
Deneb, one of the brightest stars in the sky, is a supergiant about 1,400 light-years away and is also a part of the Summer Triangle asterism. Another gem in Cygnus is Albireo, a stunning double star system located at the beak of the swan. Through a telescope, you can see the beautiful contrasting colors of these stars—one golden and the other blue.
Don’t miss the North America Nebula, located near Deneb. This emission nebula resembles the shape of the North American continent and is best viewed with binoculars or a wide-field telescope.
Next, is Scorpius, the Scorpion. This distinctive constellation is easy to identify with its hook-like shape and lies near the center of the Milky Way, making it incredibly rich in celestial objects. The heart of the scorpion is marked by Antares, a red supergiant star that is one of the largest and brightest stars in the night sky. Just west of Antares, you’ll find M4, a bright globular cluster that appears as a dense cluster of stars through a small telescope. Near the tail of Scorpius is the Butterfly Cluster, also known as M6. This open cluster is shaped like a butterfly and can be enjoyed through binoculars or a telescope.
Our final stop is Sagittarius, the Archer, which is also brimming with deep-sky objects as it lies directly in the direction of the galactic center. The constellation is easily recognizable by the asterism known as the "Teapot," which some say is “pouring out” the Milky Way.
Within Sagittarius, you can find the Lagoon Nebula, or M8, a large and bright emission nebula that is visible to the naked eye under dark skies. Through a telescope, the intricate structures of gas and dust in the Lagoon Nebula are breathtaking. Close by is the Trifid Nebula, or M20, a fascinating combination of emission, reflection, and dark nebulae. Its distinctive appearance makes it a favorite among astronomers.
Lastly, don’t miss the Sagittarius Star Cloud, also known as M24. This large star field can be seen with the naked eye and offers stunning views through binoculars, showcasing a dense region of the Milky Way.
This week’s sky
We’re starting the week with a Full Moon, which will impact our observations, since it rises just after 9 p.m. tonight. It will rise a few hours later by the week’s end and be in the sky all night and into the early morning throughout the week.
This particular Full Moon is traditionally known as the Buck Moon. The name "Buck Moon" originates from Native American, Colonial American, and European traditions. It's called the Buck Moon because this is the time of year when bucks grow their antlers.
Following the Full Moon, we enter the Waning Gibbous phase, where the moon starts to lose its fullness, but it will still be quite bright, even in the last quarter phase at the week’s end. This phase is ideal for telescopic observations of the lunar surface. The stark shadows cast by the sunlight hitting the lunar surface at a steep angle highlight the craters and mountains.
Our planets this week are still for early risers. Mars rises in Taurus around 3 a.m. Look for our red-hued neighbor in the east, just to the right and below the Pleiades cluster. Uranus is still near Mars after the conjunction they both shared last week. You’ll at least need binoculars to see it. Look for it less than 5 degrees above and to the right of Mars.
Jupiter rises about a half hour later, also in Taurus, a bit to the left of Aldebran, the red star that represents the “eye” of Taurus. At a magnitude of -1.9, it will be the brightest star in the eastern sky.
Saturn begins its march high into the eastern sky around 11 p.m. It’s still hanging out around the knee of Aquarius. Look for the Moon off to the right. Saturn will reach its highest point in the sky around 4 a.m. This will be the best time to view it through a telescope, as atmospheric turbulence can create fuzzy views of planets when they are near the horizon.
Neptune remains near Pisces and rises around midnight, leaving it high in the sky just before dawn. You’ll need a telescope to locate this blue gas giant.
Mercury and Venus are both evening stars, but they are so close to the sun it will be difficult to see them. Look for them in the western sky, low on the horizon just after sunset.
That's it for this week. Until next time, keep looking up and exploring the night sky. Clear skies, everyone!
