Observing Projects
Mercury and Venus are visible in the morning sky when it is at or near greatest western elongation and in the evening sky when at or near greatest eastern elongation. These are also the times when Venus can be seen at the highest altitude above the horizon during the hours of darkness. Mars is most easily seen around an opposition. At other times Mars may be visible only in the early morning hours before sunrise or in the early evening just after sunset. Consult such magazines as Sky & Telescope and Astronomy or their Web sites for more detailed information about when and where to look for Mercury, Venus, and Mars during a given month. You can also use the Starry Night™ program on the CD-ROM that certain printed copies of accompanies this textbook.
Refer to the Universe Web site or eBook for a link to a Web site that calculates the dates of upcoming greatest elongations of Mercury. Consult such magazines as Sky & Telescope and Astronomy, or the Web sites for these magazines, to determine if any of these greatest elongations is going to be a favorable one. If so, make plans to be one of those rare individuals who has actually seen the innermost planet of the solar system. Set aside several evenings (or mornings) around the date of the favorable elongation to reduce the chances of being “clouded out.” Select an observing site that has a clear, unobstructed view of the horizon where the Sun sets (or rises). If possible, make arrangements to have a telescope at your disposal. Search for the planet on the dates you have selected, and make a drawing of its appearance through your telescope.
This observing project should be performed only under the direct supervision of an astronomer who knows how to point a telescope safely at Mercury. Make arrangements to view Mercury during broad daylight. This is best done by visiting an observatory where the coordinates (right ascension and declination) of Mercury’s position can be used to point the telescope. DO NOT LOOK AT THE SUN! Looking directly at the Sun can cause blindness.
Refer to the Universe Web site or eBook for a link to a Web site that calculates the dates of greatest elongations of Venus. If Venus is near a greatest elongation, view the planet through a telescope. Make a sketch of the planet’s appearance. From your sketch, can you determine if Venus is closer to us or farther from us than the Sun?
Using a small telescope, observe Venus once a week for a month and make a sketch of the planet’s appearance on each occasion. From your sketches, can you determine whether Venus is approaching us or moving away from us?
This observing project should be performed only under the direct supervision of an astronomer who knows how to point a telescope safely at Venus. Make arrangements to view Venus during broad daylight. This is best done by visiting an observatory where the coordinates (right ascension and declination) of Venus’s position can be used to point the telescope. DO NOT LOOK AT THE SUN! Looking directly at the Sun can cause blindness.
If Mars is suitably placed for observation, arrange to view the planet through a telescope. Draw a picture of what you see. What magnifying power seems to give you the best image? Can you distinguish any surface features? Can you see a polar cap or dark markings? If not, can you offer an explanation for Mars’s bland appearance?
Use Starry Night™ to examine Mercury. Select Favourites > Explorations > Mercury from the menu. Stop the advance of time and use the Zoom controls and the location scroller to examine the surface of the planet Mercury. Estimate the diameter of the largest craters on Mercury’s surface by measuring their size on the screen with a ruler and comparing these diameters to the diameter of Mercury. (a) What are the diameters (in km) of the largest craters on Mercury? (b) Zoom in to examine the surface features of Mercury in more detail and compare these features with those of our Moon. Comment on the similarities and differences between these two planetary objects, neither of which has an atmosphere (e.g., presence of craters, light ray patterns, maria, peaks within craters, etc.).
Use the Starry Night™ program to observe the apparent motion of Mercury on the celestial sphere. Select Favourites > Explorations > Mercury Motion. This view, from the center of a transparent Earth, is locked and centered upon the Sun. The background stars have been removed but the planets are visible, including the inferior planets Mercury and Venus. With the Time Flow Rate set to 1 day, click the Play button and observe the motions of these two inferior planets against the background stars as seen from Earth. (a) Use the Time controls to find the first date after January 1, 2015, when Mercury is at its farthest point to the left of the Sun, and the first date after January 1, 2015, when Mercury is at its farthest point to the right of the Sun. What is your interpretation of these two dates and how would you label them? (b) If you wanted to make naked-eye observations of Mercury on these two dates, indicate the best time of day to make your observations for each date.
Use Starry Night™ to examine Mars. Open Favourites > Explorations > Mars Surface. Use the Zoom controls and the location scroller to explore this planet’s surface features. You will notice that four volcanoes (Mons) and the Valles Marineris have been labeled. (a) Which of the volcanoes appears to be the largest? (b) Right-click on Mars (Ctrl-click on a Mac) and select Markers and Outlines… from the contextual menu. In the Mars Markers and Outlines dialog window, click the lower radio button to the left of the List label. Then in the dropdown box to the right of the List label, choose Type. In the rightmost dropdown box, select Crater as the type of feature and then click the Check all Shown button. Describe the distribution of craters on the Martian surface. (c) What does the distribution of craters in the region around the volcanoes suggest about the time at which these volcanoes formed on Mars?
Use Starry Night™ to observe solar transits of Venus. Select Favourites > Explorations > Venus Transit to open a view of the sky from Rome, Italy, at 5:30:00 a.m. local standard time on June 8, 2004. The view is centered upon the planet Venus. Click the Zoom panel in the toolbar and select 1° from the drop down menu to zoom in on Venus. Select View > Hide Daylight from the menu to improve the contrast in the view. Click the Play button and watch as Venus transits the disk of the Sun. (a) What is the name given to the planetary configuration of Venus relative to Earth during this transit? (b) Select Edit > Undo Time Flow to reset the time to 5:30 a.m. Select View > Ecliptic Guides > The Ecliptic from the menu. During the transit, is Venus precisely on the ecliptic? If not, approximately how far is it from the ecliptic? [Hint: You can use the angular separation tool to measure the perpendicular distance from Venus to the ecliptic.] (c) Use the Zoom and Time controls to find as accurately as possible the times at which the transit begins and ends. What is the duration of this transit? (d) Stop time flow and select Options > Viewing Location…from the menu. In the Viewing Location dialog window, click the List tab and then the Show where radio button. In the rightmost edit box, type Fairbanks and then highlight the entry for Fairbanks, Alaska, in the list and click the Go To Location button. Change the time and date to 12:00:00 p.m. local standard time on June 5, 2012. The sky remains dark because the Hide Daylight option is still in effect. Open the Find pane and select Magnify from the dropdown menu for the Sun. Set the Time Flow Rate to 1 minute and click Play to observe this transit of Venus. Select Edit > Undo Time Flow from the menu. Right-click (Ctrl-click on a Mac) over Venus and select Centre from the contextual menu to center the view on Venus. Use the Zoom and Time Flow controls to determine the start time, end time, and duration of this transit as accurately as possible. What is the duration of this transit? (e) During the course of which of these two transits was Venus, on average, closer to the ecliptic? Explain your reasoning.
Collaborative Exercises
Figure 11-3b and Figure 11-3c show a planet in synchronous rotation and Mercury with a 3-to-2 spin-orbit coupling, respectively. Stand up and demonstrate how planets move in each of these rotations by “orbiting” around a stationary classmate who represents our Sun. How would Mercury’s motion be different if it had a 4-to-2 spin-orbit coupling instead?
In the nineteenth century, French mathematician and astronomer U. J. J. Le Verrier led a failed search for a hypothetical planet named Vulcan (after the mythical blacksmith of the gods) orbiting closer to our Sun than Mercury. If Vulcan had an orbit with the same eccentricity as Mercury’s orbit but only one-half the size, what would have been its maximum eastern and western elongations?
Figure 11-4 shows prograde and retrograde rotation. Stand up and demonstrate how Venus rotates as it orbits our Sun, using a classmate as our stationary Sun. How is this different from how Earth rotates in its orbit?
The image of Mars that opens this chapter is from the Hubble Space Telescope. Draw a circle on your paper roughly 5 cm in diameter and, taking turns, have each person in your group sketch a different region of Mars. How is your collaborative sketch different than Schiaparelli’s drawing shown in Figure 11-12?