Download CONSTELLATIONS

CONSTELLATIONS
Altitude
Ruler
The rotation of the Earth on its axis causes the stars to rise and set each evening. In
addition, the orbit of the Earth around the Sun places different regions of the sky in our
night-time view. The PLANISPHERE is an extremely useful tool for finding stars and
constellation in the sky, depicting not only what is currently in the sky but it also allows the
prediction of the rising and setting times of various celestial objects.
Horizon
10
20
30
40
THE LAYOUT OF THE PLANISPHERE
The outer circumference of the dark blue circular disk (which is called the star wheel) you’ll
notice that the wheel is divided into the 12 months, and that each month is divided into
individual dates. The star wheel rotates about the brass fastener, which represents the
North Celestial Pole. The frame of the planisphere has times along the outer edge.
Holding the planisphere on the southern corner you'll see "midnight" at the top. Moving
counterclockwise, notice how the hours progress, through 1 AM, 2 AM, and so on through
"noon" at the bottom. The hours then proceed through the afternoon and evening (1 PM,
2 PM, etc.) back toward midnight.
50
60
70
80
Zenith
Once you have the wheel set properly for the correct time and day, the displayed part represents
what you see if you stand with the star and planet locator held directly over your head with
the brass fastener toward the north. (Notice that the compass directions are also written on the
corners of the frame.) Of course, you don't have to actually stand that way to make use of the Star and
Planet Locator--this is just a description to help you understand what is displayed.
LOCATING & IDENTIFYING STARS
Stars are depicted by circles with increasing brightness represented by increasing diameter. The
planisphere is designed to be held above your head so that it represents the stars in the sky.
Hold the planisphere by the South horizon corner above your head. Notice that East is to your left and
West to your right. If you are looking North, then hold the planisphere by the North horizon. You’ll
notice that the East horizon in now on your right and West on your left.
Rotate the inner disk so that May 15 aligns with 8 pm. Slowly rotate the inner disk so that May 15
now aligns with 8 pm, then rotate it to 9 pm, then 10 pm, and so on. What direction (clockwise or
counter clockwise) do the stars move? From what horizon do the stars rise (N, S, E, W) and what
horizon do they set (N, S, E, W)?
Direction: Counter clockwise
Rise: Eastern
Set: Western
The meridian is an imaginary line that runs through the North / South horizon, bisecting the sky
into East and West horizons. List two constellations with prominent stars that can be found near the
meridian at 10 pm on January 15.
Constellation
Prominent Star(s)
Orion (The Hunter)
Betelteuse, Rigel
Auriga (The Charioteer)
Capella
Constellations
1
The stars “rotate” around a central point on the planisphere. What star do all of the stars in the sky
rotate around? What constellation is the star located?
Star Polaris (The North Star)
Constellation: Ursa Minor (The Little Bear)
ALTITUDE is a measure of the elevation an object is above the horizon. Objects on the horizon have an
altitude of 0o, and objects at an altitude of 90o are located directly overhead, or at Zenith.
Place the Altitude Ruler so that the Horizon line is on the northern horizon. Measure the altitude of
Polaris above the northern horizon.
Altitude 40o
This planisphere is designed for the night sky for locations with a latitude of 40 o N, such as
Providence. How would the altitude of Polaris change for locations north of Providence such as
Fairbanks, Alaska with a latitude of 65o N? What is the altitude of Polaris in Fairbanks?
As the latitude increases (more northerly) the altitude of Polaris increases.
The latitude of the observer is the same as the altitude of Polaris.
Fairbanks: 65o
How does the altitude of Polaris change for locations south of Providence, such as Miami, Florida
with a latitude of 25o N? What is the altitude of Polaris in Miami?
As the latitude decreases (more southerly) the altitude of Polaris decreases.
The latitude of the observer is the same as the altitude of Polaris.
Miami: 25o
Where on earth would you find Polaris on the horizon? Where would you find Polaris directly
overhead?
Horizon: Equator
Overhead: North Pole
Located on the meridian, a star or constellation at your Zenith (altitude = 90o) is directly overhead.
Vega, a bright star in the constellation Lyra (the Lyre) can be seen in April nearly directly overhead
early in the morning before the sun has risen. What time would you see Vega at your Zenith on
April 15?
5 am
Capella, in the constellation Auriga can also be found at our Zenith in the winter months. What time
would you expect to observe Capella on January 1 at Zenith?
10:30 pm
Constellations that are visible the entire year are called circumpolar constellations. Rotate the
planisphere throughout the year and record the names of four circumpolar constellations.
1. Cassioeia (The Queen)
2. Auriga (The Charioteer)
3. Cepheus (The King)
4. Ursa Major (The Big Bear)
5. Draco (The Dragon)
6. Camelopardalis (The Giraffe) (too faint to be seen)
Constellations
2
N
NNW
NNE
NW
NE
WNW
ENE
AZIMUTH is a compass direction where the object (star, planet,
sun or moon) can be found in the sky. Along with altitude,
these two measurements can accurately describe the position
of an object at a point in time.
Rotate the planisphere so that November 15 aligns with 10
E pm and find the brightest star in the sky, Sirius, located in the
constellation Canis Major. Which direction along the
ESE horizon would you look? (Be specific, such as S, SSE, SE, ESE,
etc )
SE
East Southeast (ESE)
SSE
W
WSW
SW
SSW
S
Determine the altitude of Sirius: 0o (at the horizon)
Rotate the disk so that you observe the motion of the stars every month at 9 pm until April 15.
Imagine that you walk your dog every night at 9 pm during the winter and spring months and you
were to observe Sirius during this period. Would Sirius be found in the same part of the sky
throughout the winter? Describe the changing position of Sirius during this interval of time. What
motion of the earth is responsible for this observation?
The stars make a slow migration westward throughout the year, rising earlier in the evening
each month. Sirius is found in the southeast horizon in the fall. During the winter months it
gradually rises earlier each month so that it is found higher in the sky and moving through the
southern horizon. Sirius can be found in the southwest horizon in the early spring.
Place the star Sirius in the southeastern horizon. Approximately what date of the year does Sirius
make its appearance in this horizon at sunrise (5 am)? This time of the year is referred to as the
“dog days of summer”.
Date: Early August
Rotate the planisphere to 10 pm on your birthday. What constellations and stars are prominent
near the meridian at this time of the year?
Date: October 26
Constellations
Prominent Stars
Cassiopeia, Pegasus, Aries
None 
This Red Giant Star is the red eye of the constellation Scorpius (The Scorpion): Antares
This Red Giant is the red eye of “The Bull” in the constellation Taurus: Aldebaran
The “Summer Triangle” is formed by the prominent stars Deneb, Vega, and Altair.
What constellations are these stars located?
Cygnus (The Swan)
Lyra (The Lyre [harp])
Aquila (The Eagle)
During what month can the Summer Triangle be found around midnight on the meridian?
July
Constellations
3
ASTRONOMY MEETS MYTHOLOGY
Locate and identify the following constellations.
The myth of Andromeda claims that her mother, Queen Cassiopeia, was so proud of her daughter's
beauty that she boasted it surpassed even that of the nymphs of the sea. Such arrogance offended the
gods, who released floods in retribution and threatened to destroy the kingdom. Andromeda was
chained to a rock by the sea upon the orders of her father, Cepheus, in the hope that her sacrifice to the
sea-monster Cetus would appease the gods of the sea. While awaiting her fearful fate, the princess was
heroically rescued by Perseus who exposed to Cetus the decapitated head of Medusa - a sight so
horrifying and morbid that the monster turned to stone. Pegasus was born from the union of Medusa
and Neptune when Perseus threw Medusa's head into the sea. The winged horse is famed in mythology
for creating a fountain of water at Helicon with a stamp of his hoof.
Canis Major and Canis Minor are the dogs of Orion, the hunter, which lies immediately to the northwest. In this guise they are frequently shown as a dogs standing on their hind feet, waiting on the
command of its master to spring after Lepus the hare.
THE SUN AND THE SEASONS
Located on the planisphere is a dashed line, labeled the ecliptic. This represents the path the sun
makes through the sky during the year against the background stars. Throughout the year the sun’s
altitude changes with the seasons. Since the sun rises in the east and sets in the west, the sun reaches a
maximum altitude as it passes through the southern sky at a time called solar noon when the sun is at
the meridian.
The “equator” line on the Locator is the Celestial Equator, an extension of the Earth’s equator.
These two lines intersect twice during the year. Locate the intersections when they appear in the
Southern horizon along the meridian. Record the date as they appear in the South horizon window
on the Locator. What is the significance of these dates?
March 21 & September 21
The equinox is where the sun is aligned with the Earth’s
equator. The Sun can be found directly overhead on the
Earth’s equator.
What dates are the ecliptic and equator furthest apart? What is the significance of these dates?
December 21
On the Winter Solstice the Sun (ecliptic) is found south of
the Celestial Equator. The Sun can be found directly
overhead on the Tropic of Capricorn.
June 21
On the Summer Solstice the Sun (ecliptic) is found north of
the Celestial Equator. The sun can be found directly
overhead on the Tropic of Cancer.
Rotate the planisphere to measure the altitude of the sun at noon today by placing the date in the
Southern window of the plansiphere. Use the Altitude Ruler to measure the altitude of the sun
(ecliptic) above the southern horizon.
Repeat the process for the dates in the table below.
Constellations
4
Season / Date
Altitude
Today / December 1
30o
Winter Solstice / December 21
25o
Vernal Equinox / March 21
48o
Summer Solstice / June 21
71o
Autumnal Equinox / September 21
48o
What is the change in altitude of the sun from season to season? What feature of the Earth’s
motion which is responsible for this seasonal change?
Approximately 23o each season. This is due to the tilt of the Earth’s axis.
To determine the azimuth (location at the horizon) and the time for sunrise, rotate the dial so that
today’s date is in the center of the Eastern window on the planisphere. The azimuth and time is
determined where the sun (ecliptic) intersects the horizon. Use your pencil to form a straight line
through this point and Polaris (the grommet) to estimate the azimuth and time for sunrise.
The process for sunset is similar to that above except place today’s date in the Western window.
Sunrise
Location
Sunrise
Time
Sunset
Location
Sunset
Time
Today / December 1
ESE
7:00 am
WSW
4:45 pm
Winter Solstice / December 21
ESE
7:00 am
WSW
4:30 pm
Vernal Equinox / March 21
E
6:00 am
W
6:00 pm
Summer Solstice / June 21
ENE
4:00 am
WNW
7:00 pm
E
6:00 am
W
6:00 pm
Season / Date
Autumnal Equinox / September 21
THE PLANETS
As you have seen, the dashed line on the planisphere marks the ecliptic. As our Earth moves around in
its orbit, the Sun, the Moon, and the planets also appear along this line. The ecliptic therefore
represents the plane of the solar system. Of the nine planets, five are easily visible without a telescope.
The table on the reverse side of the plansisphere contains the constellation in which a planet can be
found for during this year (2011). In the sky, the planets will appear as bright points of light, sometimes
much brighter than the surrounding stars.
Which planets are visible around 10 PM tonight (December 1)? Which planets are visible around 3 AM?
10 PM
Planet
Jupiter
Constellation
Aries (The Ram)
Altitude
60o – 70o
Azimuth
South
Constellations
5
3 AM
Planet
Mars
Jupiter
Saturn
Constellation
Leo (The Lion)
Aries (The Ram)
Virgo (The Maiden)
Altitude
40o – 50o
30o – 40o
10o – 20o
Azimuth
Southeast
West southwest
East southeast
Examine the chart again and provide an explanation why the planets Jupiter and Saturn tend to
remain in a given constellation for several months while Mars can be found in different
constellations throughout the year.
Jupiter and Saturn are at much greater distances from Earth than Mars. Jupiter and Saturn move
much more slowly against the background stars than does Mars. Mars’ orbit is relatively close to
Earth’s orbit, therefore from our perspective Mars tends to move more rapidly against the
background stars.
Why are Mercury and Venus seen only during the morning (MOR) or evening (EVE) hours?
From our perspective Mercury and Venus are located close to the Sun. We are only able to
observe these planets when the Sun is below the horizon. Therefore, at some times we can only
see Mercury and Venus before the Sun has risen in the morning or after the Sun has set in the
evening. Neither Mercury nor Venus can be seen late at night.
Constellations
6
THE PLANISPHERE: POST-LAB
1. On May 1st at 8:30 pm what prominent star is about to set in the west?
Sirius (Canis Major) or Aldebaran (Taurus)
2. On May 1st at 11:30 pm what star is near your zenith?
Arcturus (Bootes) “The Heardsman”
3. On Feb 1st at 1:00 am, what is the altitude of Polaris?
40o from the northern horizon
4. What does the ecliptic represent?
The plane of the solar system and the path of the Sun against the background stars.
It is the yearly orbit of the Earth that causes the Sun to “move”.
5. Where will the sun rise on December 25?
Where will the sun set on December 25?
6. Where will the sun rise on July 4?
Where will the sun set on July 4?
ESE
When? 7:00 am
WSW
When? 4:45 am
ENE
When? 4:30 am
WNW
When? 7:30 pm
7. What is the altitude of the sun at noon on December 25? July 4?
December 25: 25o above the southern horizon.
July 4: 70o above the southern horizon.
8. Why are only certain constellations designated as constellations of the Zodiac?
They lie along the ecliptic. The particular birthsign of the Zodiac is determined when the Sun is
located in that constellation, not when the constellation is visible in the sky.
9. What sign of the zodiac is your birthday?
October 26 (Scorpius)
10. Approximately what date would you go outside to see this constellation at midnight on the
meridian?
Early – mid June
11. What time is Orion in the southern sky today? Two months earlier? Two months later?
6:15 am (October 1)
2:15 am (December 1)
10:00 pm (February 1)
12. What two prominent stars are located in Orion? Where are they located within the
constellation?
Rigel (lower right), Betelgeuse (upper left)
13. What time does the star Sirius rise on December 1? What time does it set? How many hours is
Sirius visible in the sky on December 1?
9:00 pm (rise)
7:00 am (set)
10 hours above the horizon
Constellations
7