Kiss the Sky Tonight -- Month of September 2019
M2 (NGC 7089), the first globular cluster to be added to the Messier catalog, is located roughly 37,000 light-years from Earth in the constellation Aquarius. A globular cluster is a spherical group of stars that are bound together by their mutual gravitational attraction. M2 has a diameter of over 150 light-years and is one of the largest clusters of its kind. It was discovered in 1746 by the French astronomer Jean-Dominique Maraldi while he was observing a comet. This Hubble image of M2’s core was created using observations taken at visible and infrared wavelengths. M2 contains over 150,000 stars. Most of the cluster’s mass is concentrated at its center, with shimmering streams of stars extending outward into space. It has an apparent magnitude of 6.3 and can be seen with the naked eye in ideal viewing conditions. The best time to observe M2 is during the months of September and October. Large telescopes will resolve the cluster’s individual stars. (Credits: NASA, JPL – Caltech, and the Office of Public Outreach – STScI) (Image Credit: NASA, ESA, STScI and A. Sarajedini - University of Florida)
Kiss the Sky Tonight -- Month of September 2019
Welcome to the night sky report for September 2019 -- Your guide to the constellations, deep sky objects, planets, and celestial events that are observable during the month. In September, Pegasus becomes increasingly prominent in the southeastern sky, allowing stargazers to locate globular star clusters and a double star, Alpha Capricorni. Look for lovely crescent Moons at the start and end of the month. The September equinox brings the beginning of fall in the Northern Hemisphere. And Mars is at solar conjunction, meaning it has disappeared from night skies. The night sky is truly a celestial showcase. Get outside and explore its wonders from your own backyard.
As September brings transition from summer to fall, the sky transitions to the stars of autumn. Increasingly prominent in the southeastern sky is Pegasus, the winged horse. The Great Square of stars that outlines the body is a useful guide to the fall patterns around it.
Near the Great Square lies the sprawling pattern of Aquarius, the water-bearer. 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. It appears as a circular, grainy glow in backyard telescopes.
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.
West of Aquarius is the constellation of Capricornus, the sea goat, a figure dating back to the Sumerians and Babylonians. The star at the western end of Capricornus is Alpha Capricorni. Alpha Capricorni is an optical double but not a binary pair.
The brighter star, Algedi, is about 100 light-years away. The fainter star lies along the same line of sight but is roughly eight times farther away. The pattern hosts another globular star cluster, M30. It appears as a hazy glow in small telescopes.
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, since the globular cluster is orbiting the Milky Way in the opposite direction of most stars.
Look west to find the constellation Sagittarius, the centaur archer in the sky. Past the centaur’s arm, you will find another globular star cluster, Terzan 5. 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. The core of Terzan 5 shines brightly with the X-ray light from white dwarfs and neutron stars.
Take advantage of mild, late summer nights to enjoy the constellations and ancient globular star clusters of the September sky, as well as the Moon and planets.
We're in a several-month period right now when the new moon falls right around the end of each month. This means we get to enjoy lovely waning crescent moons at dusk for the first few days of each month, and delightful waxing crescents in the predawn sky near the end of each month.
This month, look low in the west about half an hour after sunset to enjoy the crescent moon on September 1st through the 4th, with the Moon appearing a bit higher in the sky each night. By the 5th, the first-quarter (that is, half-full) Moon winds up here, just a couple of degrees to the right of Jupiter.
At the end of the month, from September 23rd to the 27th, look east half an hour before dawn for an increasingly slimmer crescent that appears lower in the sky each day.
As you make your lunar observations, remember that for many thousands of years, the cycles of the Moon and Sun were the basis of human timekeeping. And many traditional cultures still rely on these cycles to mark special events.
A few months ago, it seemed like the Red Planet, Mars, was a constant companion in the evening sky. But as our two planets moved along in their orbits this summer, Mars has drifted further into the glare of the Sun, finally disappearing from our skies altogether in July.
From Earth's point of view, in late August and early September, Mars is more or less behind the Sun. The Sun expels hot, ionized gas from its corona, which extends far into space. This has implications for spacecraft at Mars, like NASA's Insight lander and Curiosity rover. During solar conjunction, this gas can interfere with radio signals when engineers try to communicate with spacecraft orbiting or on the planet surface, corrupting commands and resulting in unexpected behavior from our deep space explorers. To be safe, engineers hold off sending commands when Mars disappears far enough behind the Sun's corona that there's increased risk of radio interference. This event, called solar conjunction, happens about every two years. For those of us eager for a peek at Mars with our own eyes once again, it'll return to our pre-dawn skies in early November.
September 23rd marks the equinox, with day and night being of equal length. This marks the beginning of Fall in the Northern Hemisphere and Spring in the Southern Hemisphere. Although this means it's time to bid farewell to those long summer days, the upshot for stargazers is longer nights, meaning more time to look up!
From the start of the equinox until the winter solstice in December, nights become longer than days. This reduction in the number of hours of sunlight per day is what leads to seasonal cooling we associate with Fall and Winter. Of course, it's the opposite story in the Southern Hemisphere, where the September equinox ushers in the beginning of Spring.
The night sky is always a celestial showcase. Explore its wonders from your own backyard.
The following Deep Sky Objects are found in constellations that peak during the month. Some can be viewed with a small telescope, but the majority will require a moderate to large telescope. The following is adapted from my personal viewing list: "The Guy Pirro 777 Best and Brightest Deep Sky Objects."
NGC 6981 Globular Cluster M72
NGC 6994 Open Cluster M73
NGC 7009 Planetary Nebula C55, Herschel 400 H1-4 Saturn Nebula
NGC 7089 Globular Cluster M2
NGC 7293 Planetary Nebula C63 Helix Nebula
NGC 7606 Galaxy Herschel 400 H104-1
NGC 7723 Galaxy Herschel 400 H110-1
NGC 7727 Galaxy Herschel 400 H111-1
- NGC 7724 Galaxy - Paired with H111-1
NGC 7099 Globular Cluster M30
Caldwell 9 Diffuse Nebula C9 Cave Nebula
IC 1396 Open Cluster P6 Elephant Trunk Cluster
NGC 40 Planetary Nebula C2 Herschel 400 H58-4 Bow Tie Nebula
NGC 188 Open Cluster C1
NGC 2300 Galaxy P220
- NGC 2276 Galaxy - Paired with P220
NGC 6939 Open Cluster Herschel 400 H42-6
NGC 6946 Galaxy C12, Herschel 400 H76-4
NGC 7023 Open Cluster C4 Iris Nebular Cluster
NGC 7142 Open Cluster Herschel 400 H66-7
NGC 7160 Open Cluster Herschel 400 H67-8
NGC 7226 Open Cluster P140
NGC 7235 Open Cluster P7
NGC 7261 Open Cluster P8
NGC 7380 Open Cluster Herschel 400 H77-8
NGC 7510 Open Cluster Herschel 400 H44-7
NGC 7762 Open Cluster P141
IC 1434 Open Cluster P159
IC 1442 Open Cluster P160
IC 5217 Planetary Nebula P230
NGC 7209 Open Cluster Herschel 400 H53-7
NGC 7243 Open Cluster C16, Herschel 400 H75-8
NGC 7245 Open Cluster P161
NGC 7296 Open Cluster Herschel 400 H41-7
NGC 7078 Globular Cluster M15
NGC 7217 Galaxy Herschel 400 H207-2
NGC 7331 Galaxy C30, Herschel 400 H53-1
NGC 7448 Galaxy Herschel 400 H251-2
NGC 7457 Galaxy P173
NGC 7479 Galaxy C44, Herschel 400 H55-1
NGC 7814 Galaxy C43
IC 4684 Diffuse Nebula P182
IC 4725 Open Cluster M25
IC 4776 Planetary Nebula P183
NGC 6440 Globular Cluster Herschel 400 H150-1
NGC 6445 Planetary Nebula Herschel 400 H586-2 Little Gem Nebula
NGC 6469 Open Cluster P184
NGC 6494 Open Cluster M23
NGC 6507 Open Cluster P185
NGC 6514 Diffuse Nebula M20, Herschel 400 H41-1 Trifid Nebula
NGC 6520 Open Cluster Herschel 400 H7-7
NGC 6522 Globular Cluster Herschel 400 H49-1
NGC 6523 Diffuse Nebula M8 Lagoon Nebula
NGC 6528 Globular Cluster Herschel 400 H200-2
NGC 6530 Open Cluster P49
NGC 6531 Open Cluster M21
NGC 6540 Globular Cluster Herschel 400 H198-2
NGC 6544 Globular Cluster Herschel 400 H197-2
NGC 6546 Open Cluster P106
NGC 6553 Globular Cluster Herschel 400 H12-4
NGC 6558 Globular Cluster P107
NGC 6561 Open Cluster P186
NGC 6563 Planetary Nebula P187
NGC 6565 Planetary Nebula P248
NGC 6567 Planetary Nebula P188
NGC 6568 Open Cluster Herschel 400 H30-7
NGC 6569 Globular Cluster Herschel 400 H201-2
NGC 6583 Open Cluster Herschel 400 H31-7
NGC 6590 Open Cluster P50
NGC 6603 Open Cluster M24 Small Sagittarius Star Cloud
NGC 6613 Open Cluster M18
NGC 6618 Open Cluster M17 Omega Nebula
NGC 6624 Globular Cluster Herschel 400 H50-1
NGC 6626 Globular Cluster M28
NGC 6629 Planetary Nebula Herschel 400 H204-2
NGC 6637 Globular Cluster M69
NGC 6638 Globular Cluster Herschel 400 H51-1
NGC 6642 Globular Cluster Herschel 400 H205-2
NGC 6645 Open Cluster Herschel 400 H23-6
NGC 6647 Open Cluster P108
NGC 6652 Globular Cluster P31
NGC 6656 Globular Cluster M22
NGC 6681 Globular Cluster M70
NGC 6715 Globular Cluster M54
NGC 6716 Open Cluster P109
NGC 6717 Globular Cluster P110
NGC 6723 Globular Cluster P52
NGC 6809 Globular Cluster M55
NGC 6818 Planetary Nebula Herschel 400 H51-4
NGC 6822 Galaxy C57 Barnard’s Galaxy
NGC 6864 Globular Cluster M75
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