Observing Projects
After looking at the beautiful color photographs of nebulae in this chapter, you may find the view through a telescope a bit disappointing at first, but fear not. You can see a great deal with even a small telescope. To get the best view of a dim nebula using a telescope, use the same “averted vision” trick we described in “Observing tips and tools” in Chapter 17: If you direct your vision a little to one side of the object that you are looking at, the light from that object will go onto a more sensitive part of the retina.
Use a telescope to observe at least two of the H II regions listed in the following table. In each case, can you guess which stars are probably responsible for the ionizing radiation that causes the nebula to glow? Can you see any obscuration or silhouetted features that suggest the presence of interstellar dust? Draw a picture of what you see through the telescope and compare it with a photograph of the object. Take note of which portions of the nebula were not visible through your telescope.
| Nebula | Right ascension | Declination |
|---|---|---|
| M42 (Orion) | 5h 35.4m | –5° 27′ |
| M43 | 5h 35.6m | –5° 16′ |
| M20 (Trifid) | 18h 02.6m | –23° 02′ |
| M8 (Lagoon) | 18h 03.8m | –24° 23′ |
| M17 (Omega) | 18h 20.8m | –16° 11′ |
| Note: The right ascensions and declinations are given for epoch 2000. | ||
On an exceptionally clear, moonless night, use a telescope to observe at least one of the dark nebulae listed in the following table. These nebulae are very difficult to find, because they are recognizable only by the absence of stars in an otherwise starry part of the sky. Are you confident that you actually saw the dark nebula? Does the pattern of background stars suggest a particular shape to the nebula?
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| Nebula | Right ascension | Declination |
|---|---|---|
| Barnard 72 (the Snake) | 17h 23.5m | –23° 38′ |
| Barnard 86 | 18h 02.7m | –27° 50′ |
| Barnard 133 | 19h 06.1m | –6° 50′ |
| Barnard 142 and 143 | 19h 40.7m | –10° 57′ |
| Note: The right ascensions and declinations are given for epoch 2000. | ||
A few fine objects cover such large regions of the sky that they are best seen with binoculars. If you have access to a high-quality pair of binoculars, observe the North American Nebula in Cygnus and the Pipe Nebula in Ophiuchus. Both nebulae are quite faint, so you should attempt to observe them only on an exceptionally dark, clear, moonless night. The North America Nebula is a cloud of glowing hydrogen gas located about 3° east of Deneb, the brightest star in Cygnus. While searching for the North America Nebula, you may glimpse another diffuse H II region, the Pelican Nebula, located about 2° southeast of Deneb. The Pipe Nebula is a 7°-long, meandering, dark nebula to the south and to the east of the star θ (theta) Ophiuchi, which is in a section of Ophiuchus that extends southward between the constellations of Scorpius and Sagittarius. Located about 12° east of the bright red star Antares, you can locate θ Ophiuchi using the Starry Night™ software.
Use the Starry Night™ program to examine the Milky Way Galaxy. Open Favourites > Explorations > Star forming regions. The view looks toward the center of the Milky Way from the center of a transparent Earth. The view also displays the galactic equator and the constellations. Observe the mottled appearance of the Milky Way caused by regions of opaque dust and gas. Click on the Options tab, expand the Deep Space layer and click the checkbox to turn Nebulae On. Click on the + sign to the left of Nebulae to expand this layer. Click Off all the checkboxes for the Nebula options except that for Dark Nebula. Numerous dark nebulae visible in Earth’s night sky are shown with green outlines or markers. (a) Use the hand tool and zoom controls to look around the view and describe the distribution of these dark nebulae in the sky. (b) Now click Off the Dark Nebula option in the Options pane and click On the Emission Nebula. Again use the hand tool and zoom controls to look around the sky and observe the distribution of these nebulae and describe your observations. (c) Use the Find tool to locate and identify several of the more prominent emission nebulae: M8, M20, NGC 3372, M42, and NGC 7000 (North American Nebula). Magnify each of these nebulae in turn and describe your observations of the details of some of them, such as color, shape, and structure. (d) Zoom out again to return to the wide-field view and use the hand tool to find the tight knot of emission nebulae between the constellations of Ursa Major and Draco. Zoom in on this region to a field of view about 1° wide. You will notice that the outlined emission nebulae belong to the galaxy M101 (the Pinwheel Galaxy), which is about 27 million ly from Earth. Describe the distribution of these emission nebulae within this galaxy and compare it to your observations of the distribution of emission nebulae in the Milky Way. (e) Given the distance to M101, what does the fact that these emission nebulae in this galaxy are visible from Earth suggest about their properties?
Use Starry Night™ to examine the H-R diagram of the Pleiades star cluster. This group of stars was formed relatively recently in astronomical time. Select Favourites > Explorations > Pleiades to display this cluster of young stars in the view. Click on the Status tab to display the H-R diagram of all stars in this field of view around the Pleiades. Note that this appears to be similar to that of stars in our local neighborhood. However, if you restrict the distance to display only the stars within this localized cluster, a different pattern emerges. Click on the Distance cut-off checkbox in the H-R Options layer of the Status pane to restrict the distance to a range between 320 and 420 ly. (a) Where on the H-R diagram do you now find the majority of the stars of this cluster? (b) In view of the existence within this cluster of very hot stars with high output of energy, what does this tell you about the age of this cluster compared to the general population of stars?
Collaborative Exercises
Imagine that your group walks into a store that specializes in selling antique clothing. Prepare a list of observable characteristics that you would look for to distinguish which items were from the early, middle, and late twentieth century. Also, write a paragraph that specifically describes how this task is similar to how astronomers understand the evolution of stars.
Consider advertisement signs visible at night in your community and provide specific examples of ones that are examples of the three different types of nebulae that astronomers observe and study. If an example doesn’t exist in your community, creatively design an advertisement sign that could serve as an example.
The pre–main-sequence evolutionary tracks shown in Figure 18-10 describe the tracks of seven protostars of different masses. Imagine a new sort of H-R diagram that plots a human male’s increasing age versus decreasing hair density on the head instead of increasing luminosity versus decreasing temperature. Create and carefully label a sketch of this imaginary H-R diagram showing both the majority of the U.S. male population and a few oddities. Finally, draw a line that clearly labels your sketch to show how a typical male undergoing male-pattern baldness might slowly change position on the H-R diagram over the course of a human life span.
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