Telescope Targets
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Jupiter
Jupiter is seen here with its famous Great Red Spot, its largest moon Ganymede (top), its most volcanically active moon Io (right), and Io's shadow (dark spot on Jupiter). Jupiter is currently located in Taurus, the constellation of the bull. At a mass of roughly 318 Earth masses, Jupiter is the most massive body in the solar system after the Sun. It takes Jupiter just under 10 hours to rotate; thus, one could observe the entire planet from the time it rises to the time it sets. Jupiter also has 95 known moons, and you can see up to four of the largest (the Galilean moons) on any given night including tonight. Jupiter also bears one of the most famous storms of all time – the Great Red Spot. This anticyclone has been observed for hundreds of years and was once large enough to swallow three Earths. Over time, the Great Red Spot has varied in color, shape, and size and is now only about the size of a single Earth.
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The Clown Nebula
The Clown Nebula as seen with Dyer Observatory's Seyfert Telescope. Found near the hip of the twin Pollux in the constellation Gemini, the Clown Nebula, formally known as NGC 2392, is a grand example of a planetary nebula. Despite the name, this type of object has nothing to do with planets save for a somewhat similar appearance to some of the planets in a telescope. What we are seeing is the remains of a small star that has met its demise. Though many mistakenly believe that all stars explode when they expire, the majority of stars are too small to go supernova in their final moments. Most stars, including our own Sun in five billion years, will go through a couple of stages of swelling to many times their original size, becoming red giants and then asymptotic giant branch (AGB) stars. At this point, the outer layers of a star are very weakly held by the gravity of the collapsed core and are gently lost to space over thousands of years. During this process, the white-hot core, known as a white dwarf, is exposed to space. The copious ultraviolet light emitted by the small core is absorbed by the expanding outer layers, causing them to fluoresce like a cosmic neon sign. This is precisely what is happening in NGC 2392 and others like it. The white dwarf, seen at the center of the nebula, is only the size of Earth but over 100,000 times as massive as our planet. A spoonful of white dwarf on Earth would weigh as much as elephant! NGC 2392 is about 1.5 light-years in diameter and lies approximately 6,500 light-years from Earth.
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Izar (Double Star)
The double star Izar in the constellation Bootes is a splendid double star. The different temperatures of the stars result in orange and blue hues that contrast well with one another. Credit: S. Smith/CloudyNights.com Izar is the second brightest star in the constellation Boötes, the herdsman, and is found just to the north of the red giant star Arcturus, the fourth-brightest star in the night sky. A telescope with an aperture at least a few inches in diameter is needed to show Izar as a double star. The binary system resides about 203 light-years away. With the angular separation seen on the sky, this means the two stars are physically separated by about 185 astronomical units (about six times the Sun-Neptune distance) and complete an orbit around each other about every millennium.
The brightest of the two stars, Izar A, is nearing the end of its life. With a mass about four times greater than that of the Sun, it has swelled to about 40 times the size of the Sun and is about 650 times as luminous. With a temperature nearly 2,000°C cooler than the Sun, it has taken on a more orange hue as it has evolved. Izar A's companion, Izar B, still has a ways to go before it begins evolving. Though it has just over twice the mass and radius of our Sun, it shines nearly 50 times as bright. Its higher temperature gives it a notably whitish-blue appearance that contrasts nicely with the warmer coloration of its partner, making this one of the loveliest double stars of the spring season.
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Polaris - The North Star
Polaris as viewed through a backyard telescope. Polaris A, the brightest star, is easily visible to the unaided eye. Polaris B, the dimmer star, requires a telescope to be spotted. A third star, Polaris C, is lost in the glare of Polaris A. Credit: Les Ewan/Stargazerslounge.com One of the most famous stars in the night sky (but not necessarily the easiest to find) is Polaris, better known as the North Star. Many people mistakenly believe that Polaris is the brightest star in the night sky. Not so - that title belongs to Sirius, which lies in our southern sky. In fact, there are about 50 other stars that shine brighter than Polaris in the evening sky. Polaris forms the end star of the handle of the Little Dipper and is easily found with the aid of the Big Dipper. A line connecting the two end bowl stars of the Big Dipper (Dubhe and Merak) will point toward Polaris.
Polaris has some interesting characteristics, but it is most notable because of its position in our sky. In more modern times, Polaris lies very close to the north celestial pole - the point about which the sky appears to rotate due to Earth's rotation on its axis. Over time, however, Earth wobbles around like a top because of the gravitational tug from the Moon and Sun, completing one wobble in approximately 26,000 years. As a result, the star nearest the north celestial pole has not always been and will not always be Polaris. For example, when the Great Pyramid of Khufu was being construction about 4,500 years ago, Thuban, a moderately bright star in the constellation Draco, was nearest the north celestial pole. In about 12,000 years, Vega, the fifth brightest star in the night sky, will be the closest bright star to the north celestial pole.
When you look up at Polaris, you are actually looking at a system of three stars located about 446 light-years away. The main star you see, known as Polaris A, is a yellow supergiant star that is about 40-45 times as wide, 3-4 times as massive, and, on average 2500 times as luminous as our sun. But what do we mean by "on average?" Polaris A is a special type of star known as a Cepheid variable. This type of star is named after the first of its kind to be found, delta Cepheus. These stars have evolved to a point where they pulsate, physically changing in size over a matter of days, weeks, or months. As they pulsate their luminosities change. In the early part of the 1900s, astronomer Henrietta Swan Leavitt noted that there was a relationship between the true luminosities of Cepheid variables and the time it takes them to pulsate. This result would become incredibly important to astronomers because now had a tool that would allow them to determine the distances to very remote Cepheids. All they would have to do is measure the apparent brightness over time to determine the pulsation period and then look up the corresponding true luminosity. The apparent brightness and the true luminosity are related through the distance of the star. Since Cepheids are supergiants, they are extremely luminous and can be see in neighboring galaxies - once we have a distance to the Cepheid, we know the distance to its home galaxy.
Through the modest telescope one can also observe a fainter companion star, known as Polaris B. This star is similar to our Sun in size and temperature, being only slightly larger and somewhat hotter. Astronomer Sir William Herschel, discoverer of many objects including the planet Uranus, discovered Polaris B in 1779. This star takes several tens of thousands of years to complete one orbit in the system since its typical orbital distance is about 80 times larger than Neptune's average distance from the Sun (2.7 billion miles).
In 1929, the Polaris star system was discovered to harbor a third companion. This star, known as Polaris Ab, is almost identical to Polaris B but orbits much closer to Polaris A, so it is typically lost in the glare of its much brighter companion. In this case "closer" is a relative term - Polaris A and Polaris Ab are about as far from each other as Uranus is from our Sun. Its presence was noted when astronomers decrypted the information encoded in the spectrum of Polaris A and found the spectroscopic signature of a second star.
So how do you find Polaris? Within Ursa Minor (the constellation of the little bear) lies the asterism (a familiar, easy-to-spot part of a constellations) of the Little Dipper, and Polaris marks the end of its handle. Though Polaris is the brightest star in Ursa Minor that doesn't mean it is very easy to spot. In light-polluted skies, the Little Dipper is not very easy to find as most of its stars are pretty faint. On the other hand, one of the easiest asterisms to locate is the Big Dipper, an asterism of the constellation Ursa Major, the Big Bear - most of its stars are pretty bright. Find the two end stars of the bowl of the Big Dipper, known as Merak and Dubhe. Connect these two stars (known as the "pointer" stars) with a line and continue up from the lip of the Big Dipper. The line will take you right to Polaris. Since Polaris is so close to the north celestial pole, its altitude above your horizon is the same as your latitude. If you live to the south of the equator - sorry, you never get to see the North Star.
Artist rendering of the Polaris star system. Credit: NASA/ESA/HST, G. Bacon (STScI)
Key Points of Interest
The map below will provide locations for key points of interest in the observatory. If you have any questions, please don't hesitate to ask a staff member or volunteer.
- Garland Collection - Many of the original astronomy instruments obtained by Chancellor Landon Garland in the 1870s for use in the first physics and astronomy classes of Vanderbilt University.
- Star Model - An interactive model that displays information and positions of the 100 nearest and 100 brightest stars in the night sky as well as information about our own star, the Sun.
- Fused-Quartz Mirror Disk - One of two original, uncoated test mirrors for the 200" Mount Palomar Observatory that were given to Vanderbilt University. One was originally intended to be used in a new telescope of Vanderbilt University.
- Seyfert Telescope - On clear nights, the 24" Seyfert Telescope will be viewing a selected target. On cloudy nights, the doors will be open for visitors to see and learn about Dyer's largest telescope.
- Hallway Images - Large infographics about galaxies, the Milky Way, and the life cycles of stars. On the opposite wall is a high-resolution panorama of the Milky Way with constellations and deep-sky objects highlighted.
- HST Model & Planetarium Dome - Learn about the Hubble Space Telescope with the 1/5th scale model suspended in Dyer Observatory's original planetarium dome and experience the dome's acoustics.
- AstroCantus - A combination of art and science, AstroCantus is a series of chimes that sound as the stars pass overhead. NOTE: The chimes may be muted - ask a volunteer.
- ViewSpace Presentation - A presentation from the Space Telescope Science Institute. The program consists of continuous presentations ranging in length from five to 20 minutes and covering a variety of topics. Visitors may come and go as they please during the presentation.
- Meteorites & Tektites - A collection of various types of meteorites and tektites.
Sky Chart for April 18, 2025
- April 3rd – 10:30PM CDT
- April 18th – 9:30PM CDT (The Moon/planets are shown for this date)
- May 3rd – 8:30PM CDT
Deep Sky Objects
Stars and Constellations
General Information About the Sky
The ecliptic is the imaginary line that the Sun follows through our sky. In reality, this line is dictated by the orbit of the Earth. Since all of the planets of the solar system lie in nearly the same plane, one will observe the planets positioned very close to or on this line as well. Because the Moon’s orbit is tilted just a bit more than five degrees to this line, the Moon will not stray far from the ecliptic either. Some objects, such as comets, will not stay around the ecliptic. The constellations through which the ecliptic passes are the 12 famous zodiac constellations. There are, however, 13 constellations through which the Sun passes. For the first two weeks of December, the Sun is located in the constellation Ophiuchus, the serpent bearer.
There are 88 official constellations that cover the entire sky. Some are never visible from Tennessee as we are too far north; however, some, such as Ursa Minor and Camelopardalis, are circumpolar – they never get low enough in the sky to disappear below our horizon. The rest of the constellations are seasonal and visible in the evening sky for certain months of the year. Constellations are not just the stick figures we sometimes imagine connecting the brighter stars but are instead entire areas of the sky – everything is in a constellation. Objects outside of our solar system (stars, nebula, clusters, galaxies) remain in constellations, but the Moon, Sun, planets, comets, and asteroids all move through the constellations over time. Some famous star formations, such as the Big Dipper, Little Dipper, and Great Square of Pegasus, are not constellations – they are very recognizable parts of constellations known as asterisms. The Big Dipper, for example, is just a part of the constellation Ursa Major, the great bear.
Our Sun is just one of about 300 billion stars that make up our home galaxy, the Milky Way (shown in light grey in the sky map). In the late evenings of winter and summer, the Milky Way can be seen overhead. In the late summer, we are looking towards the center of the galaxy, which appears somewhat brighter. In the late winter, we are looking away from the center. Our solar system is situated on its side about halfway out from the center of this barred spiral galaxy.
When the Milky Way is easily visible, we have an opportunity to see many examples of the different types of objects found in the disk of a spiral galaxy. Spiral galaxies contain large amounts of dust and gas from which stars can form. As these clouds of material, known as nebulae, begin to collapse, denser pockets within the nebulae collapse faster to produce stars. When the stars begin to shine, they illuminate the clouds from which they formed. A prime example for late autumn to early spring is the Great Orion Nebula (M42), which forms the second “star” in the sword of Orion, the hunter. As time goes on and star formation uses up the remaining material of a nebula or disperses it, all that will eventually remain is a cluster of a few hundred to several thousand stars. These clusters, known as open clusters, are dominated by hot, blue-white stars and highlight the spiral arms of galaxies like our own. The Pleiades Cluster (M45), also known as “Subaru” or the “Seven Sisters,” is a beautiful example of such a cluster. The proximity of the cluster makes about six of its members easily visible to the unaided eye, but a low-power telescope will show dozens more.
The more massive a star is, the shorter its life will be. Massive stars therefore do not have enough time to venture far from the disk of the galaxy before ending their lives in spectacular supernovae. One such star, which was observed to explode in 1054 A.D., formed the Crab Nebula (M1). Most stars, however, are not massive enough to die explosively; instead, they puff up to become red giants and then gradually shed their outer layers over thousands of years. Once the core of the dying star is exposed, its ultraviolet light causes the shed layers to fluoresce, producing a beautiful planetary nebula. These nebulae have nothing to do with planets, rather their shape sometimes resembles the outer planets. Excellent examples of planetary nebulae are the Ring Nebula (M57), Clown Nebula (NGC 2392), and Cat’s Eye Nebula (NGC 6543).
During the late spring and autumn, the Milky Way appears closer to the horizon. Our galaxy, like all spiral galaxies, is shaped like a disk and is fairly thin compared to its width. As a result, when we see the Milky Way near the horizon, we are able to look up and out of our galaxy relatively easily to see objects outside of it. These include other spiral galaxies, like the Whirlpool (M51) and Andromeda (M31) galaxies, and spherical- to football-shaped galaxies known as elliptical galaxies, such as M87. Orbiting around these galaxies are globular clusters such as the Hercules Cluster (M13) and the Pegasus Cluster (M15). These clusters contain anywhere from a few hundred thousand to over a million stars in a small volume.