Part II

The Planisphere as a Tool

The planisphere can be used as a tool to predict the way the sky will look at any time and date. In this activity you will use a planisphere to answer a series of questions about the night sky. In addition you may use The Sky software (or other planisphere software, if available) and the Internet to aid you in answering the questions and constructing your own original illustrations.

The planisphere has no way to show the movement of the Sun (which blocks our view of the stars during the day). You will have to be conscious of the rising and setting of the sun as a factor in answering the questions. Also, daylight savings time is in effect at certain times of the year. When it is in effect drop the planisphere back by one hour to view the sky as it actually will be.

Useful Information

Some of the following questions require you to remember material covered in class or to use your textbook or other sources to look up the answers. All questions assume that you are observing the sky from a northern hemisphere mid-latitudes location such as Scarborough, Maine. Use a separate piece of paper to answer the questions. Some questions require you to draw a picture. All questions should be answered carefully and thoroughly: you will be tested on the information you learn in the course of answering the questions.

1. What is the north celestial pole (NCP)? What important star in the sky is near the NCP?
2. What is the celestial equator? What is the south celestial pole? Draw a picture to illustrate your answers to these and the previous question.
3. What is the meridian? What is it called when stars, planets, the sun or the moon crosses the meridian?
4. What is the zenith? What is the nadir?
5. What is altitude?
6. What is azimuth? How does the azimuth of an astronomical object depend on the observer’s location (latitude and longitude)? Choose a star on your planisphere and consider how its altitude and azimuth changes for people in different time zones. Draw pictures to illustrate your answer.
7. What is the Winter Solstice defined in terms of the location of the Earth in its orbit and the tilt of the Earth? What effect does this geometry have on the weather in the northern hemisphere of the earth? On the southern hemisphere?
8. Define the Summer Solstice in the same way.
   Read more about the solstices here.
9. Define the equinoxes, Spring and Fall, in the same way.
   Read more about equinoxes here.
10. What is the ecliptic? Draw a picture to illustrate your answer.
11. What constellations does the Sun pass through as it travels along the ecliptic?
12. What name does this collection of constellations have? When, that is, during what month(s), does the Sun pass through each constellation?
13. Look up the dates given in books of Astrology for each Sun Sign (the signs of the Zodiac). Compare them to the times when the Sun is actually in those constellations. What’s going on?
14. Draw a picture of the ecliptic and show the location of the sun against the background of stars and using the celestial equator and celstial poles at each solstice and equinox. You should include at least the constellations of the Zodiac. Label the month during which the Sun passes through each constellation. (Hint: draw a rectangle with lines like a mercator projection map showing vertical lines similar to longitude lines and horizontal lines like latitude lines. The line of 0° latitude is the celestial equator. The ‘latitude’ lines are called Declination. The ‘longitude’ lines are called Right Ascension. Zero degrees Right Ascension is the point which we call the spring equinox.)
15. What constellations are visible during the Summer months (June, July, August) from 9 pm to midnight? During what months are these constellations visible from 2 am to 5 am?
16. What constellations are visible during the Fall months (September, October, November) from 9 pm to midnight? During what months are these constellations visible from 2 am to 5 am?
17. What constellations are visible during the Winter months (December, January, February) from 9 pm to midnight? During what months are these constellations visible from 2 am to 5 am?
18. What constellations are visible during the Spring months (March, April, May) from 9 pm to midnight? During what months are these constellations visible from 2 am to 5 am?
19. How many angular degrees does the sky move through each day? Calculate the number of degree the sky moves each hour.
20. How many angular degrees does the Sun move each day? Each month? Each season? Use your illustration of the ecliptic to answer these questions.

Further Reading