Tonight's Sky: September
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In September the sky transitions to the stars of autumn. Use Pegasus to find Alpha Capricorni, Algedi, and several star clusters. Also watch for the Harvest Moon. Watch “Tonight’s Sky” to learn about this month’s constellations—including space-based views.
Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, NASA Jet Propulsion Laboratory, and Sonoma State University.
- Starfield images created with Stellarium
- Mythological constellations from Firmamentium Sobiescanium sive Uranographilia by Johannes Hevelius, courtesy of the United States Naval Observatory
Musical track The Far River written by John Serrie, from the album And the Stars Go With You, courtesy of New World Music, Ltd.
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Text, September. Tonight's sky. Constellations. Stylized drawings of a lion, a ram, and a bull. East, 9 PM. Looking up into a night sky filled with stars. Text, As September brings transition from summer to fall, the sky transitions to the stars of autumn. A constellation with lines between stars forming a large square with three limbs protruding upwards. Text, Increasingly prominent in the southeastern sky is Pegasus, the winged horse. A drawing of the horse charging upwards into the sky appears over the constellation, its head and two front legs protruding up. Text, The great square of stars that outlines the body is a useful guide to the fall patterns around it.
Text, September. Tonight's sky. Constellations. Stylized drawings of a lion, a ram, and a bull. East, 9 PM. Looking up into a night sky filled with stars. Text, As September brings transition from summer to fall, the sky transitions to the stars of autumn. A constellation with lines between stars forming a large square with three limbs protruding upwards. Text, Increasingly prominent in the southeastern sky is Pegasus, the winged horse. A drawing of the horse charging upwards into the sky appears over the constellation, its head and two front legs protruding up. Text, The great square of stars that outlines the body is a useful guide to the fall patterns around it.
To the right of Pegasus, a constellation appears made up of a long curved snaking line with a branched line extending down from its middle. Text, Near the great square lies the sprawling pattern of Aquarius, the water bearer. A drawing of a kneeling man pouring out a jug of water appears over the constellation. Text, Located within the western part of the constellation is M2, one of the oldest and largest globular star clusters associated with the Milky Way galaxy. Near Aquarius' head, M2 shines brightly. Text, It appears as a circular grainy glow in backyard telescopes.
Image of M2, a densely packed cluster of bright white stars with almost no black visible behind them at the center. Text, Visible light. NASA's Hubble Space Telescope has imaged the cluster, a compact globe of some 150,000 stars that are more than 37,000 light-years away. At approximately 13 billion years old, this cluster formed early in the history of the universe and offers scientists an opportunity to see how stars of different masses live and die. Results from ESA's Gaia satellite suggest that this cluster, along with several others, may have once belonged to a dwarf galaxy that merged with the Milky Way.
To the right of Aquarius, a constellation appears made of an upward arching line with two triangle shapes pointing down from it. Text, West of Aquarius is the constellation of Capricornus, the sea goat, a figure dating back to the Sumerians and Babylonians. A drawing of a horned goat with a fish's tail appears over the constellation. Text, The star at the western end of Capricornus is Alpha Capricorni. The star at the top of the goat's head. An image of two stars close together. Text, Ground-based view. Alpha Capricorni is an optical double but not a binary pair. The brighter star, Algedi, is about 100 light-years away. The fainter lies along the same line of sight, but is roughly eight times farther away. The pattern Capricornus hosts another globular star cluster: M30. An image of a dense star cluster. Text, Ground-based view. It appears as a hazy glow in small telescopes.
An image of M30, tightly clustered white and blue stars, brighter at the center and spreading out into blackness. Text, Hubble Space Telescope visible light. Stars are packed so closely in globular clusters that they can interact with each other. Binary stars can exchange partners in their tight gravitational square dance. More massive objects like black holes and neutron stars move toward the center. M30 likely started life with another galaxy that merged with our own. The globular cluster is orbiting the Milky Way in the opposite direction of most stars.
Look west of Capricornus to find the constellation Sagittarius, the centaur archer in the sky.
A constellation forming a two-legged creature pointing a long bow and arrow in one arm. A drawing of a man with the body of a horse and the muscular torso of a man appears over the constellation, pointing the bow and arrow. Text, Past the centaur's arm, you will find another globular star cluster, Terzan 5. An image of Terzan 5, a cluster of white, orange, and bright blue stars, more dense in the middle. Text, Hubble Space telescope, visible light. Terzan 5 sits near the dark dust lanes of the Milky Way. Bright blue young stars are visible in the foreground of the ancient cluster.
A closer slightly blurry image of a cluster of spherical orange, blue, and red stars. Text, Chandra X-ray Observatory X-ray light. The core of Terzan 5 shines brightly with the X-ray light from white dwarfs and neutron stars. Take advantage of the mild late summer nights to enjoy the constellations and ancient globular star clusters of the September sky. Celestial wonders await you in tonight's sky.