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Messier 24

The Small Sagittarius Star Cloud provides a window into the depths of the Milky Way galaxy

distance

10,000 light-years

apparent magnitude

4.6

constellation

Sagittarius

Object type

Star Cloud

A thick field of stars on the black background of space. The stars are blue, red and white and fill the screen.
This detailed Hubble view of Messier 24 captures a huge number of stars in only a tiny portion of the region, which is also known as the Small Sagittarius Star Cloud.
NASA, ESA, and R. Sahai (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)

Messier 24 (M24) is unusual for being not a specific object but a strikingly clear space between dust clouds through which a glittering host of stars are visible: a glimpse into the Sagittarius spiral arm of our Milky Way galaxy. From where our solar system resides, clouds of cosmic dust obscure our view into the Milky Way, but the Small Sagittarius Star Cloud ― as M24 is also known ― provides a tunnel-like view into the starry depths of our galaxy. The 600-light-year-wide window opens onto stars some 10,000 to 16,000 light-years distant. A tiny portion of the star cloud is visible in this pair of Hubble views of the region, yet a multitude of different types and colors of stars are apparent. The entirety of M24 encompasses a number of nebulae and star clusters (not visible in these close-up images).

Charles Messier entered M24 in his catalog of night sky sights in 1764, terming it “a large nebulosity in which there are many stars of different magnitudes.” It appears as a hazy patch with the unaided eye, though binoculars or a telescope can resolve its stars.

Two images are in the frame. The right is a pinkish nebula with a vast number of stars with some clouds of gas and dust. The left is a field of bright individual stars, which vary in color and include red, blue and white stars. The image on the left pinpoints the region where the more detailed right image is located.
The ground-based image (left) of M24 shows the location of the Hubble view (right).
Ground-based image: KPNO/NOIRLab/NSF/AURA/F. Calvert/A. Block Hubble image: NASA, ESA, and R. Sahai (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)

These Hubble images were taken as part of a study of preplanetary nebula ― a brief, dim, and infrequently seen early stage in the death of a Sun-sized star. Planetary nebulae are glowing, intricate remains of Sun-sized stars, so called because early astronomers thought they looked like planets through telescopes of the time. In the preplanetary nebula stage, the star has shed its outer layers of gas, but the star’s core is not yet hot enough to ionize those layers and cause them to glow.

A field of stars of various colors, including red, white and blue. Some dark patches are scattered among the thickly collected stars.
Another view of a tiny portion of the Small Sagittarius Star Cloud gives a glimpse into the depths of the Milky Way galaxy, mostly unobscured by the dust clouds that normally block our view from Earth.
Credit: NASA, ESA, and R. Sahai (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)
Two images are in the frame. The right is a pinkish nebula with a vast number of stars with some clouds of gas and dust. The left is a field of bright individual stars, which vary in color and include red, blue and white stars. The image on the left pinpoints the region where the more detailed right image is located.
The ground-based image (left) of M24 shows the location of the Hubble view (right).
Ground-based image: KPNO/NOIRLab/NSF/AURA/F. Calvert/A. Block Hubble image: NASA, ESA, and R. Sahai (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)

In the night sky, the Small Sagittarius Star Cloud is about nine times larger than the Moon. Its dense concentration of stars can be seen in binoculars, but telescopes will better resolve the stars into a jewel-like collection of varying brightnesses. The best time to observe it is during summer months in the Northern Hemisphere. It is in the winter sky for Southern Hemisphere observers. It is located south of Messier 17, or the Omega Nebula.

A star chart showing the location of M24 among line drawings of the constellations Aquila, Ophiuchus, Sagittarius, and Scorpius. South is indicated at the bottom of the image along with the date, August at 10 p.m.
This star chart for M24 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium
A star chart showing the location of M24 among line drawings of the constellations Cygnus, Lyra, Aquila, Sagittarius, and Ophiuchus. North is indicated at the bottom of the image along with the date, August at 10 p.m.
This star chart for M24 represents the view from mid-southern latitudes for the given month and time.
Image courtesy of Stellarium

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