Reading an Evening Star Map

Background

Let’s start with the instructions given on the star map we use here. Wrapped around the outside of the circle that represents the night sky on a certain date and time we read:

“The sky map shows the entire night sky from horizon-to-horizon as it appears on certain days and times. The center of the map is the part of the sky directly overhead (zenith) and the outer circle is the horizon. Celestial objects are located between the zenith and the horizon. Compass directions are indicated along the horizon circle (for example ‘North’). Turn the sky map around its center (just as you are doing now) so the compass direction that appears along the bottom of the map is the same direction that you face. Begin by using the sky map to find a bright star pattern in the sky.”

The evening sky map also contains a sky calendar for the month. This one includes facts about the location of the Moon, a total eclipse of the Moon, details of the Eta Aquarid meteor shower, and the planets Mars, Mercury, Saturn, and Venus. The reverse side of the map has information about the celestial objects one could see on this date and time, tips for observing the night sky, an astronomical glossary, the stars that are easily seen with the naked eye, those objects easily seen with binoculars, and those that need a telescope to view.

Question: What is represented by the center of the sky map? a. the horizon  b. the zenith   c. the celestial north pole

Learning Goals

• Be able to define the basic words describing the celestial sphere.
• Recognize how stars move over the course of a night.
• List constellations that will be visible at the given date and time.
• Identify constellations that lie on the celestial equator, within the plane of the galaxy, and along the ecliptic.

Part 1: Astro Lingo–Define the following:

Part 2: Reading an Evening Sky Map

We mentioned in the background that there are many versions of sky maps available to those wanting to learn more about finding celestial objects. These maps can be found at the back of astronomy textbooks, online, at bookstores, and elsewhere. The latest issue of “The Evening Sky Map,” the site used to get the star map used here, shown in Figure 1, as an example, May 2022 for northern latitudes between 40° and 55° N latitudes, can be found at https://www.skymaps.com.

The last page of this activity contains the large sky map. Make sure you have it in hand to find the objects we describe here. Constellations are identified using all capital letters (for example, LEO). Some of the brightest stars are labeled with their proper names (for example, Arcturus and Regulus) or Greek letter designation (as in b Scorpii, the second brightest star in the constellation Scorpius). The edge of the circle represents the horizon, the center, the zenith. The ecliptic is marked with dashed line, starting at Scorpius. The “deep sky objects” present in this night sky are identified; the symbol key is given at the lower right.

Figure 1. Part of the star map for a given date and time in May, with the celestial equator given. Please refer to the full map, located on the last page of this activity, for more details.

Use the large map given on the last page of this activity as you work through the following steps. Figure 1 gives examples of what your version of the large map should look like when you are finished.

• Draw a vertical line from the north to the south horizons. This becomes the meridian, dividing the western and eastern skies. Label it as the meridian.
• Draw a horizontal line from the east to west horizons. Label the intersection as your zenith at this given date and time.
• Find the north star Polaris and draw an arrow to it or circle it, see Figure 1.
• In Figure 1, the long, curved arrow represents the direction the celestial objects move over the course of a day–rising in the east and setting in the west.
• The celestial objects lying in the Milky Way, our galaxy, are in the shaded area running along the horizon at this date and time: from west, around the northern horizon, to the east and southeast.
• Find the ecliptic on the large map, shown as a dashed line passing through Gemini; circle the word “ecliptic.”
• Find the celestial equator on the large map and note where it intersects the ecliptic. Stars and other celestial objects that lie on the celestial equator take 12 hours to rise and set.

Questions

1. Which constellation is highest in the sky (at the zenith) at this date and time?

2. Name a large constellation that will be crossing the meridian in about 4 – 5 hours.

3. What is one constellation that is viewable now but will not be in 4 – 5 hours?

4. List three constellations that lie within the plane of the Milky Way (the shaded region).

5. List two constellations that the ecliptic passes through.

6. List three constellations that lie on the celestial equator:

7. Which constellation lies both on the celestial equator and the ecliptic?

8. What is special about the place on the celestial sphere where the celestial equator and ecliptic intersect?

9. List three of the brightest stars on this map (those having the largest black circle), those given their proper names besides Arcturus and Regulus.

10. List three open star clusters, two galaxies, and one planetary nebula that are in the sky at this date and time, giving each Messier number.

• 11. Open star clusters:
• 12. Galaxies:
• Planetary nebula

11. Some stars as seen from northern latitudes are circumpolar, meaning they never set. These stars circle counterclockwise, centered very close to Polaris. Ursa Major, Ursa Minor, and Draco are well known circumpolar constellations. Additional circumpolar constellations would be seen close to the northern horizon on this map. List three of them.

Part 3: Summary

13. Please evaluate the usefulness of this sky map in an essay, using the reverse side of this sheet. Possibly include comments about:

• Which objects were the easiest to find?
• Which objects were difficult to find?
• What was something new that you learned?
• Would you be able to teach someone new to astronomy how to use it?
• What object or objects are you interested in finding out more about?

Be sure to find an evening sky map for the current month and note the approximate times the map would be most applicable at the start and end of the month. Print it out, grab a red flashlight, and head outdoors on a clear, dark night and find celestial objects galore!

Print and enlarge the front and back as needed from web site mentioned above.