University of Michigan - Department of Astronomy

Name: Partner(s): Day/Time: Version: southern

Southern Constellations

To the right hand I turned, and fixed my mind Upon the other pole, and saw four stars Ne'er seen before save by the primal people.

Rejoicing in their flamelets seemed the heaven. O thou septentrional and widowed site, Because thou art deprived of seeing these!

--Dante Purgatorio: Canto I

Objectives


 

Introduction

Origin of the Southern Constellations

There are 88 constellations officially recognized by the International Astronomical Union, each of which has official boundary lines to divide up the sky. Fifty-two of the constellations have origins in Ptolemy's Almagest catalog (ca. AD 150). The remainder, including the constellations of the deep south, were invented by Europeans of the 17th and 18th centuries. Star catalogs and constellations created by the Dutch explorers, Frederick de Houtman and Pieter Keyser, were mapped by their countryman, Petrus Plancius in 1598. These Dutch constellations represented flora and fauna of the East Indies and Madagascar. Johannes Hevelius, the Polish astronomer and cartographer, invented 7 northern and equatorial constellations that received IAU endorsement. These were published in his famous atlas, Firmamentum Sobiescanum in 1690. The prolific French astronomer Nicolas Louis de Lacaille catalogued and created the remaining 14 of the standard constellations in 1754, which represent tools of science and art.

A prominent southern Ptolemaic constellation was Argo Navis, the ship Argo of the Greek hero Jason, and the Argonauts. This constellation was so huge that it was divided into three smaller constellations, Puppis, the Stern; Carina, the Keel; and Vela, the Sails.

The most distinctive southern constellation is Crux, the Cross, which is also known as the Southern Cross. This constellation was visible to the ancient Greeks before 1000 BC, and considered part of the constellation Centaurus, the Centaur. However, due to precession (see the Precession Activity), Crux slipped below the horizon in the ancient world, and was not included in Ptolemy's list. Crux was later known anecdotally by 16th century European sailors, and was officially included as a constellation by Plancius.

Another noteworthy Plancius constellation is Indus, the Indian Man. Since the Dutch explorers went to Madagascar and the East Indies, Indus by his name clearly represents a native of the East Indies, today's Indonesia. Plancius originally represented Indus with only a loincloth and spears. Later cartographers represented him with feathers, the attribute of Native Americans.

Many people consider the southern sky to be more splendid to the naked eye than the north. Among the treasures to be seen are the two largest satellites of our Milky Way Galaxy, the Large and Small Magellanic Clouds. They are clearly visible to the naked eye, indeed appearing like small clouds. Another interesting object is the largest globular cluster in the Galaxy, ω Cen, which is so huge that it may represent the core of a dwarf galaxy whose stars have been tidally stripped off. Also in Centaurus is the nearest Sun-like star, α Cen. The center of our Galaxy transits at a much higher altitude in the southern hemisphere, enhancing the visibility of the many nebulae and clusters in that direction. In this activity, you will explore constellations and features of the southern sky.

Constellation Visibility

Recall that circumpolar constellations are those that are close enough to the celestial pole that they remain mostly above the horizon all the time as the sky turns (See Figure 1, for the northern hemisphere). The other visible constellations are seasonal constellations that rise and set (see the Out of Seasons Constellations activity). You know that the seasons in the southern hemisphere are reversed from those in the northern hemisphere. (This is explored in detail in the Seasons Activity.) So how does your latitude affect which parts of the sky, and which constellations, you can see, and when?  

Figure 1: Equatorial grid for the northern hemisphere.

Coordinate System grid

Altitudes and Declinations for an observer in the northern hemisphere Figure 2: Relation between latitude, declination, and visibility. The observer is standing at latitude l on the Earth, in the northern hemisphere.

Figure 2 shows how the visible range of declination on the sky is related to your latitude. The northern-most declination visible for the northern hemisphere is dec = 90º, the north celestial pole. The figure shows how your zenith always has a declination equal to your latitude (l). Your horizon is 90° from your zenith, and so the southern-most declination visible, set by your horizon, is dec = l-90º. (For the southern hemisphere, the northern-most declination visible is l+90, for negative l.)

Now consider the circumpolar constellations. As seen in Figure 2, the altitude of the north celestial pole is also equal to your latitude l (recalling from the Coordinate Systems activity that altitude is measured up, from the horizon). This means that circumpolar stars must have an angular distance from the pole less than l. It may be helpful to refer to Figure 1 as well.

Resources


Southern Constellations: Worksheet

Part 1: Constellation Visibility

  1. Your GSI will show the sky in Ann Arbor (lat 42º N) at midnight on March 21, which is the northern spring equinox. Determine whether you see each of the constellations in Table 1 on the next page. Fill in the row for Ann Arbor. If a constellation is visible and it is also circumpolar, write "C". Otherwise, write "Y" or "N" for the visibility. If the constellation is visible, also write its declination in the first row.
  2. Your GSI will adjust the sky to show how it appears on the same date, at the other two locations, the equator and Santiago, Chile. At each location, the GSI will turn the sky through one night, so you can observe the rotation of the sky at each location. Continue completing the Table.
Table 1: Constellation Visibility
Location Ursa Major Leo Corvus Crux

Ann Arbor

lat 42º N

       

Equator

lat 0º

       

Santiago

lat 33º S

       

  1. Does your latitude affect a constellation's visibility?

  2. Can people in Ann Arbor and Santiago see any of these same constellations on the same night? If so, which one(s)?

  3. The GSI will point out the position of the South Celestial Pole. Is there a pole star analogous to Polaris?

Part 2: Identifying Constellations on the Sky

  1. Your GSI will divide you into groups, and will give each group a laser pointer. S/he will set the planetarium sky for Santiago, Chile (latitude 33º S) on the following dates: April 1, Fall; Oct 1, Spring.

  2. In your groups, identify which constellations are visible in the shown season. Note that the constellations are listed in order of RA. Find the general direction in which to look for each constellation visible in this season. Include both altitude and azimuthal direction.  For example, you might say high in the south, or low in the west-northwest (WNW).  Enter this in Table 2. In each group, each person should be responsible for identifying at least one object in each season for the next part of the activity. In the "Origin" column, specify whether the constellation is due to Ptolemy and the ancient Greeks (G), Plancius and the Dutch explorers (D), or Lacaille (L).

  3. Your GSI will call on your group to point out one of the objects. The person in your group who is responsible for that object should use the laser pointer and point out the object for the class.

  4. When all the objects for that season have been pointed out, your GSI will identify additional objects from the list below. Mark the location of these on your star charts. Note the type of object for each one.


    Small Magellanic Cloud: __________________________

    Large Magellanic Cloud: __________________________

    ω Centauri: _______________________________

    The False Cross: __________________________

  5. The GSI will move the planetarium to the next season. Repeat the above steps to find your next object and point it out to the class. Look out for any constellations that may appear in both seasons. Make two entries for these constellations.
Table 2: Some Southern Constellations

 

Name Represents Season Direction
1 Eridanus The River Eridanus    
2 Grus The Crane or Hornbill    
3 Indus The Indian Man    
4 Octans The Octant    
5 Ara The Altar    
6 Centaurus The Centaur    
7 Crux The Cross    
8 Vela Sails of Argo    
9 Carina The Keel of Argo    



Concluding Questions:

  1. Can you see southern constellations (having negative declinations) from the northern hemisphere? Explain.






  2. In the northern hemisphere, Polaris can be used to identify the north celestial pole. Review your answer to Part 1 Question 5. Why don't both poles have a pole star?




  3. From which location on Earth can you see more constellations throughout the year: the equator, the south pole, or do you see the same number from both places? Explain.






  4. Is Orion visible at night in the southern hemisphere during the same months of the year as in the northern hemisphere? The same seasons as in the northern hemisphere? Explain.






  5. What range of declination is seen as circumpolar from Santiago? Explain and show your work. Which constellations from Table 2 are circumpolar from Santiago?







Updated: 8/28/14 by SAM & MSO

Copyright Regents of the University of Michigan.