ASTR& 101 Lab
Celestial Coordinates
Name: ________________________
Use your planisphere and star maps to complete this exercise.
Locating Constellations
The constellation that is at the zenith at 9 PM tonight is: __________________________________.
The zodiac constellations completely visible at 9 PM tonight are: _______________________________.
Locating Planets
The brightest planet observable at 9 PM tonight is ______________ in the constellation _____________.
The first planet to rise sometime after 9 PM tonight is ____________ in the constellation ____________,
and it will rise at _______________.
Locating the Sun
Today, the Sun was closest to the ___________ (Greek letter) star in the constellation ________________.
The Sun rose this morning at the time _______ AM and sets tonight at the time ______________.
Astrological Signs
(Check today’s online or in print newspaper for today’s Horoscope.)
If you had been born on this date then your astrological sign is ___________________, which starts on the _____ day
of the month ____________ and ends on _____ day of the month _______________.
In fact, the Sun enters this constellation on the _____ day of the month ____________ and ends on the _____ day of
the month _______________.
Why is there such a discrepancy between the Horoscope dates and the actual Sun location dates?
Circumpolar Constellations
Five constellations that are observable from this latitude at any time of night on any day of the year are:
__________________________________________________________________________.
Two constellations that are never observable from this location are: ______________________________.
(Hint: May need to go beyond using the planisphere . Check out the constellation chart of the Southern Region.)
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Measuring Angles
Many astronomy observations involve measuring angles. All angular measurements are based on a circle.
Altitude and Azimuth: The Altazimuth Coordinate System
Azimuth
A full circle is divided into 360° (degrees). When measuring your azimuth, or compass direction, north is at 0°, east is
at 90°, south is at 180°, and west is at 270°.
Examples
If you are looking toward the northeast, then what is your azimuth?
Northeast is halfway between north (0°) and east (90°), so northeast = 45° azimuth.
If you look southwest, your azimuth is how many degrees?
South = 180°, west = 270°, therefore halfway between = 225°.
Your azimuth is 285°. Which direction are you looking?
270° = west, so at azimuth = 285° you are looking a little bit north of west, also called WNW.
Problems
If you look southeast, then the azimuth is _____? If you look slightly west of south, the azimuth is _____?
If your azimuth is 315°, you are looking toward the _______. Your azimuth I 20°; you are looking _______.
Altitude
Altitude, the angle between the horizon and an object in the sky, is measured as part of a quarter circle going from
the horizon to the zenith, a point directly overhead.
Examples
The altitude of an object at the zenith is ____°?
The angle between a point directly overhead and the horizon is 90°.
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The altitude and azimuth of an object on the south horizon is ______, _______, respectively?
The angle between a point on the horizon, and the horizon itself, is 0°. The azimuth of any object to the south is 180°.
The altitude of an object halfway between the horizon and the zenith is ____?
The angle between a point halfway up to the zenith from the horizon, and the horizon itself, is 45°.
Problems
A planet to the southeast, two-thirds of the way up to the zenith, is at azimuth _______, altitude _____.
A star to the west-northwest, one third of the way up to the zenith, is at azimuth ______, altitude _____.
From a viewpoint on Earth located at latitude at 0 N°, Polaris (the North Star) is at azimuth _______, altitude _____.
From a viewpoint on Earth located at latitude at 48 N°, Polaris (the North Star) is at azimuth _______, altitude _____.
From a viewpoint on Earth located at latitude at 90 N°, Polaris (the North Star) is at azimuth _______, altitude _____.
Positions on the Celestial Sphere in Celestial Coordinates: Right Ascension and Declination
Celestial coordinates pinpoint locations on the celestial sphere . Celestial coordinates work same way latitude and
longitude do on the surface of the Earth. The celestial equator is directly above the Earth’s equator. The celestial
poles are directly above Earth’s north and south poles.
Right ascension (RA) is like longitude on Earth. Right ascension measures positions east of the vernal equinox. The
vernal equinox has an RA of 0 (zero).
Right ascension (RA) is measured in hours, minutes, and seconds instead of degrees. The abbreviated units are h
(hours), m (minutes) and s (seconds). Just like with time, there are 60 minutes in one hour and 60 seconds in one
minute. However, these are not time units, these are units for locations in space as seen on the celestial sphere.
Each hour of right ascension (RA) is 1/24 of a circle. One hour of RA spans 15° along the celestial equator. However,
just like longitude lines (meridians) do on Earth, units of RA get closer and closer to each other as they approach the
celestial poles. Therefore, 1 hour of RA only spans 15° along the celestial equator, and spans fewer and fewer
degrees the closer one gets to the celestial poles.
Declination (dec) is the angle north of (+) or south of (-) the celestial equator. The north celestial pole is at
declination +90°.
The constellation charts that you have been provided copies of show the celestial sphere coordinates.
Examples
What are the celestial coordinate positions of the summer solstice?
RA = 6h, dec +23° 24’. This can be concluded from the following facts. The summer solstice lies one-quarter of the way
around the celestial sphere, or 6h of right ascension, from the vernal equinox, and is at the furthest north (+) position
on the ecliptic (+23° 24’, where we are using the slightly rounded off number of +23.4° and changing it from a decimal
angle to an angle in degrees, minutes, seconds, which are symbolized for angles as °, ‘, “, respectively).
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What are the celestial coordinates for  Boötis (Arcturus)?
RA = 14h 15m, dec = +19° 30’. The constellation Boötes is on the 0h to 12h Equatorial Region constellation chart. The
star is 15m beyond the 14h right ascension mark (each graduation on the equator = 5 minutes). The star is halfway
between the +19° and +20° declination marks that run along the right edge of the chart.
What is the star that is located at 11h 2m, +56°?
 Ursa Majoris Locate this point on the North Circumpolar Region constellation chart. You can find the  star in
Ursa Major. Its common name is Merak.
Problems
What are the celestial coordinates of  Lyrae? ____________________
The Sun on November 1? _______________________
 Ceti (Diptha)? ______________________
The Sun today? _______________________
What star is located at 21h 30m, -5°? _______________ What star is located at 0h 9m, +15°? ________________
Fill in the celestial coordinates of right ascension (RA) and declination (dec) for each of the locations listed in the
table below.
Object
vernal equinox
RA
dec
Object
 Orion
summer solstice
 Ursa Major
autumnal equinox
 Capricornus
winter solstice
 Scorpius
zenith at noon today
north point on horizon at
noon today
zenith at midnight today
north point on horizon
at midnight tonight
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RA
dec
Mapping Tonight’s Constellations Using a Planisphere or Star Wheel
Set your planisphere (star wheel) for 8:00 PM tonight. Mark N, S, E and W on the outside edge of the planisphere
oval, depicted below.
Using the planisphere as your reference, in the oval below draw the following constellations: URSA MINOR, URSA
MAJOR, CASSIOPEIA, ORION, CANIS MAJOR, CANIS MINOR, GEMINI, AURIGA, TAURUS, PERSEUS, AND LEO. Label
each constellation with its name. Label (use arrows if need be) the bright stars Polaris, Dubhe, Betelgeuse, Rigel,
Sirius, Aldebaran, Capella, and Regulus.
Which constellation is each of the following bright stars in?
Polaris _____________ Dubhe____________ Betelgeuse _____________ Rigel _______________
Sirius ______________ Aldebaran____________ Capella ____________ Regulus _______________
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Set your planisphere for 5:00 AM tomorrow morning.
Mark N, S, E and W on the outside edge of the planisphere oval, depicted below.
Using the planisphere as your reference, in the oval below draw the following constellations: URSA MINOR, URSA
MAJOR, CASSIOPEIA, BOÖTES, LEO, VIRGO, HERCULES, LYRA AND CYGNUS.
Label each constellation with its name.
Label (use arrows if need be) the bright stars Polaris, Dubhe, Arcturus, Regulus, Vega, and Deneb.
Which constellation is each of the following bright stars in?
Arcturus _________________ Vega _________________ Deneb _________________
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