10.7: Accessible Descriptions

Figure 10.1.1 Interstellar Matter

A wide-field image of interstellar gas and dust surrounding the star Antares in the constellation Scorpius.

Image Elements

• Antares, the brightest star in the image, appears at lower left surrounded by reddish nebulosity.
• To the right of Antares is the globular cluster M4, seen as a dense scattering of faint stars.
• At center left, a bright star is surrounded by the blue glow of a reflection nebula.
• At center right, another bright star is surrounded by red emission nebulosity.
• A dark nebula snakes across the image above these two stars, blocking the light from stars behind it.
• At top center, a bright star is surrounded by a large area of blue reflection nebulosity, criss-crossed by dark dust lanes.

Credit: ESO/Digitized Sky Survey 2

Figure 10.2.1 Orion Nebula

A Hubble Space Telescope image of the Orion Nebula, a bright star-forming region of glowing gas and dust.

Image Elements

• Large areas and bright swirls of glowing red gas fill most of the image, criss-crossed by dark bands of dust.
• A cluster of hot young stars lies at the bright center of the nebula, where the gas glows most intensely.
• A bluish tint appears along some of the outer edges of the gas clouds, produced by dust scattering light from the hot stars.
• Dark, irregular patches of dust are silhouetted against the brighter glowing gas throughout the image.

Credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA), and the Hubble Space Telescope Orion Treasury Project Team

Figure 10.2.2 Spectrum of an Interstellar Dust Cloud

A diagram illustrating how an interstellar dust cloud adds absorption lines to starlight passing through it.

Diagram Elements

• A star, labeled Star, is shown at the left, emitting a wavy line representing its light traveling to the right.
• An arrow at the right, labeled To observer, shows the direction the light travels.
• A gas cloud, labeled Interstellar dust cloud, is drawn in the center of the diagram, with the star's light passing through it.
• Between the star and the cloud, a Stellar spectrum is shown with three broad, dark absorption lines from the star's own atmosphere.
• Between the cloud and the observer, a composite spectrum is shown containing the same three broad stellar lines, plus many additional narrow lines produced by the interstellar cloud.

Figure 10.2.3 The 21-Centimeter Line

A diagram comparing the spin directions of the proton and electron in a hydrogen atom.

Panel (a)

• A blue sphere at the center represents the proton, with an upward arrow showing its spin axis and a circular arrow showing it spinning to the right.
• A smaller blue dot on the surrounding ellipse represents the electron, also with an upward spin arrow and a circular arrow spinning to the right.
• The proton and electron spin in the same direction, representing the slightly higher-energy aligned state.

Panel (b)

• A blue sphere at the center represents the proton, with an upward arrow showing its spin axis and a circular arrow spinning to the right.
• A smaller blue dot on the surrounding ellipse represents the electron, with a downward spin arrow and a circular arrow spinning to the left.
• The proton and electron spin in opposite directions, representing the slightly lower-energy anti-aligned state.

Figure 10.2.4 Vela Supernova Remnant

An image of the expanding remnant of a supernova explosion in the constellation Vela.

Image Elements

• Delicate, thread-like filaments of orange and reddish gas curve across the center and lower portion of the image.
• Diffuse patches of blue and orange nebulosity surround the filaments, marking gas heated by the explosion's shock wave.
• Countless faint background stars are scattered across the entire field.

Credit: Digitized Sky Survey, ESA/ESO/NASA FITS Liberator, Davide De Martin

Figure 10.2.5 Fullerene C60

A three-dimensional model of a fullerene C60 molecule.

Diagram Elements

• Sixty carbon atoms are shown as dark spheres, connected by cylindrical bonds.
• The atoms are arranged in a pattern of alternating pentagons and hexagons that form a hollow, ball-like cage, similar in shape to a soccer ball.

Figure 10.2.6 Barnard 68

A visible-light image of the dark interstellar cloud Barnard 68.

Image Elements

• A solid black, comma-shaped region fills the center of the image, completely blocking the light of any stars behind it.
• Thousands of background stars of varying brightness and color surround the dark cloud on all sides.

Credit: ESO

Figure 10.2.7 Horsehead Nebula in Orion

Two images comparing the Horsehead Nebula in visible and infrared light.

Image (a)

• On the left, a visible-light image shows the horsehead-shaped dark cloud silhouetted against a bright red nebulous background.
• A very bright star, Zeta Orionis, appears at the upper left.
• Fainter swirls of gas and dark dust fill the lower half of the image.
• Credit: ESO and Digitized Sky Survey

Image (b)

• On the right, an infrared image of the same region shows a near reversal of the visible-light view.
• The bright star seen in Image (a) is barely visible.
• The horsehead shape now appears bright against a darker background.
• The lower half of the image is bright with wisps and swirls of gas and a bright star-forming nebula near the center.
• Two inset panels show the horsehead and the bright nebula in greater detail.
• Credit: NASA/JPL-Caltech

Figure 10.2.8 Milky Way in Infrared

An infrared image of a long strip along the plane of the Milky Way Galaxy.

Image Elements

• A diffuse greenish-blue glow of interstellar dust, emitting at 3.6 and 8.0 microns, fills the entire image.
• Bright, circular reddish patches, emitting at 24 microns, mark regions where dust has been warmed by nearby young stars.
• Irregular dark patches and tendrils of the densest, coldest dust are scattered throughout the field, appearing dark even at these infrared wavelengths.

Credit: NASA/JPL-Caltech/University of Wisconsin

Figure 10.2.9 Pleiades Star Cluster

An image of the Pleiades star cluster and the reflection nebula that surrounds it.

Image Elements

• Several bright blue-white stars are scattered across the image, each surrounded by a hazy blue glow.
• Faint wisps of blue nebulosity connect and surround the stars, similar in appearance to fog around a streetlamp.
• Countless fainter background stars are visible throughout the image.

Credit: NASA, ESA and AURA/Caltech

Figure 10.2.10 Barnard 68 in Infrared

An infrared image of the same dark cloud, Barnard 68, shown in visible light in Figure 10.2.6.

Image Elements

• The comma-shaped region that appeared completely black in the visible-light image is now filled with faint reddish points of light.
• These points are background stars whose infrared light, at a wavelength of 2.2 microns, is able to penetrate the dust of the cloud.
• Countless brighter foreground stars surround the cloud, as in the visible-light image.

Credit: ESO

Figure 10.2.11 Scattering of Light by Dust

A diagram illustrating how interstellar dust scatters blue light more than red light.

Diagram Elements

• A star is drawn at the far left, and an arrow at the far right, labeled To observer, shows the direction of travel.
• Two waves emerge from the star: a short-wavelength blue wave and a long-wavelength red wave, both moving to the right.
• An interstellar dust cloud, drawn as a fuzzy disk containing small scattered dots, sits between the star and the observer.
• Inside the cloud, the blue wave strikes several dots and scatters upward and downward, away from the observer.
• The red wave passes through the cloud unimpeded, continuing on toward the observer.

Figure 10.2.12 Interstellar Dust Grain Model

A diagram showing the structure of a typical interstellar dust grain.

Diagram Elements

• An irregular white blob at the center, labeled Core, represents the rocky or graphite core of the grain.
• A semi-transparent bluish-gray layer surrounding the core, labeled Mantle, represents the icy outer layer.
• Three molecules are labeled within the mantle: H₂O, CH₄, and NH₃.

Figure 10.3.1 Distribution of Interstellar Matter

A computer simulation of the distribution of interstellar gas across the Milky Way Galaxy, viewed from above.

Image Elements

• The galaxy is shown from a top-down view, with gas arranged in a spiral pattern resembling the arms of a hurricane.
• Greenish colors, making up most of the image, represent neutral hydrogen gas.
• Yellow regions within the spiral arms mark the densest concentrations of gas, where giant molecular clouds have formed.
• Blue, low-density holes scattered through the arms mark regions cleared out by supernova explosions.

Credit: Mark Krumholz

Figure 10.4.1 X-Ray Sky

An all-sky map showing X-ray emission surrounding the Sun, made by the ROSAT satellite.

Image Elements

• The image is an oval, all-sky projection with the dark, dusty plane of the Milky Way running horizontally across the center.
• Blue regions, representing 1.5-kiloelectron-volt X-rays, are scattered along the lower portion of the dark band of the Milky Way.
• A circular green region, representing 0.75-kiloelectron-volt X-rays, extends above and below the dark band near the center of the image.
• A faint red glow, representing 0.25-kiloelectron-volt X-rays, covers the entire image, including areas away from the galactic plane.

Credit: NASA

Figure 10.4.2 Local Fluff

A diagram of the patches of interstellar gas surrounding the Sun, known as the Local Fluff.

Chart Elements

• The vertical axis is labeled Distance (light years) and runs from -20 to 20 in increments of 10.
• The horizontal axis is labeled Distance (light years) and also runs from -20 to 20 in increments of 10.
• The Sun is plotted at the center of the diagram (0, 0) as a yellow circle.
• A gray arrow points from the Sun toward the upper right, labeled Direction of sun's motion.

Labeled Features

• Two nearby stars are plotted: Alpha Centauri, a yellow dot near (4, -4), and Sirius, a blue dot near (-8, -8).
• A blue arrow along the bottom of the diagram points to the right, labeled Galactic Center.
• Several interstellar cloud regions are named: the Local Cloud near the Sun, Blue near the bottom center, and the G Cloud to the right of the Sun.
• Five unlabeled arrows above the Sun point to the upper left, indicating the motion of parts of the local cloud.
• An additional unlabeled arrow near (-2, -2) points upward.
• Arrows labeled with nearby constellations point outward from various parts of the cloud, indicating the direction each part is moving: Mic near (1, 20) pointing left, Hyades near (-10, 10) pointing upward, Aur near (-12, 4) pointing left, and Gem near (-11, -3) pointing left.
• The constellations Aql, Eri, and Oph are labeled to the right and slightly above the Sun.

Figure 10.5.1 Mercury Space Suit

A Mercury program space suit from the early 1960s.

Image Elements

• A silver, form-fitting space suit stands upright against a black background.
• A rounded white helmet with a dark visor sits atop the suit, connected to the body by a flexible hose.
• A NASA logo patch is visible on the chest of the suit.

Figure 10.5.2 Fictional Space Suit

A fictional space suit worn in the 1968 film 2001: A Space Odyssey, on display in a museum exhibit.

Image Elements

• A silver-gray, padded space suit hangs on display inside a glass case.
• The suit has a rounded fabric hood in place of a rigid helmet, along with padded joints at the shoulders, elbows, and knees.
• Worn boots and gloves are visible at the bottom and sides of the suit.
• Museum placards and other exhibit items are visible in the background.

Figure 10.5.3 Trust in Science

A line graph tracking Americans' confidence in the scientific community from the 1970s to the 2020s, separated by political party.

Chart Elements

• The vertical axis is labeled 'Great deal' of confidence in scientific community (%) and runs from 0 to 70 in increments of 10.
• The horizontal axis shows years from 1970 to 2020.
• A blue line labeled Democrats fluctuates between roughly 35% and 45% from the 1970s to the 2010s, then rises sharply to a peak of about 65% around 2020 before falling back to around 50% in the most recent years.
• A red line labeled Republicans fluctuates between roughly 35% and 50% from the 1970s to the 2010s, then declines steadily after about 2015 to around 23% in the most recent years.
• The lower right corner of the chart is labeled Current Opinion in Psychology, citing the chart's source.

Figure 10.5.4 Moon Joy

A photograph of the Artemis II crew sharing a moment of celebration aboard the Orion spacecraft.

Image Elements

• Four crew members are gathered in a tight group hug, floating in microgravity inside the spacecraft.
• American and Canadian flags are mounted on equipment above the crew.
• Cargo nets holding blue and orange storage bags line the walls of the cabin.
• Various spacecraft equipment, cables, and stowed items are visible throughout the background.