# A112LB/114LB

Date: Score: ( / 75)

Name(s):

CELESTIAL SPHERE AND READING CHARTS AND MAPS

Note: This lab may be done in class or may be assigned as an at-home activity. It combines indoor work with outdoor observations.

“For my part, I know nothing with any certainty,

but the sight of stars makes me dream.” – Vincent van Gogh

Objective: Learn to use star charts and planispheres to identify objects in the night sky and determine their visibility on a given date and time.

## Equipment/Resources:

All-sky star chart with constellations labeled Planisphere, also called a sky wheel

Ruler or straightedge Paper and pencil Calculator

## Instructions:

This lab is an indoor lab that has an outdoor component. If the sky is clear, you will complete the observations after you’ve finished the indoor part. If not, complete it on your own, as directed by your instructor. Weather can be

## INTRODUCTION

You may recall from lecture or your textbook that the Celestial Sphere is a way of describing the sky and locations on the sky by imagining that all celestial objects are at the same distance, painted on the inside of a giant sphere. The figure below shows some of the key points on the celestial sphere.

Outdoors, it is often convenient to describe the location of something in the sky by stating the direction you need to be facing to be pointed at it,

A112LB/114LB Manual Ed. 1 F2018

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and how far above the horizon it is. The direction you need to face is the azimuth, and the number of degrees you need to look up is the altitude. This is called an altitude- azimuth, alt-azimuth or alt-az coordinate system. This is convenient to describe where

something is right now at your current location. This is similar to describing directions to a location from your current location. The figure below shows altitude- azimuth coordinates.

We describe where things are on the Earth using a map. Star charts are maps of the sky. Star charts describe where objects in the sky are in a way that is independent of observer location. Reading them is just like reading a map. You can successfully read one without really understanding how the system works, but when it is time to use the telescopes, it will be

## helpful to understand how the system works.

Maps on Earth typically use latitude and longitude to locate places. The equivalent of latitude and longitude for the sky is called the equatorial coordinate system. The figure below shows the

equatorial coordinate system (R.A. and DEC).

The projection of Earth’s equator onto the sky is called the celestial equator. The projection of Earth’s north pole on the sky is called the north celestial pole.

A sky chart also has a measurement north or south of the equator called declination (Dec or DEC). Declination is equivalent to latitude.

Star charts also have a coordinate equivalent to longitude called right ascension (RA or R.A.). It measures how far an object is to the east or west of a reference point called the vernal equinox. The vernal equinox refers to the location of the Sun against the background stars at the time of the spring, or vernal, equinox. Right ascension is measured in degrees or hours. It takes 24 hours for a star to make a complete circuit of the sky. That means that it takes 24 hours to travel 360° and 1 hour of right ascension = 15°.

## REVIEW TERMINOLOGY

( /4) 1: Fill in the blanks: The point directly overhead is referred to as the

, and the point below your feet is the . The point directly above the Earth’s north pole is the . If you stood on the Earth’s equator for a long time with a laser pointer directed straight up, you would be tracing out the

.

( /5) 2: How would you use altitude and azimuth to describe the position of the Moon when it is setting at a point very close to due west?

( /5) 3: When astronomical catalogs are written, the objects in them usually have positions listed as Right Ascension and Declination. Why would a catalog not use altitude and azimuth?

· Locate a star chart or charts with the constellations labeled. You may need more than one chart for all the objects. Spend some time getting used to the scale. Note if R.A. is hours, degrees, or both.

( /4) 4: Determine the R.A. and DEC for the following stars as accurately and precisely as you reasonably can:

a. Deneb (Alpha Cygnus) R.A.: DEC:

b. Arcturus (Alpha Boötes) R.A.: DEC:

c. Antares (Alpha Antares) R.A.: DEC:

d. Betelgeuse (Alpha Orionis) R.A.: DEC:

( /5) 5: Are the following constellations are in the northern, southern, or both celestial hemispheres?

a. Ursa Major

b. Cygnus

c. Gemini

d. Pegasus

e. Scorpius

f. Orion

g. Libra

h. Boötes

i. Centaurus

j. Virgo

( /4) 6: Using the star charts, find the names for the stars nearest the following coordinates:

R.A. DEC Name

 a. 18hr 35m +38d 44m b. 05hr 15m – 08d 00m c. 06hr 45m – 17d 00m d. 03hr 45m +24d 00m

( /4) 7: Give an approximate range for R.A. and DEC for the following constellations:

Canis Major R.A. to DEC to

Delphinus R.A. to DEC to

· On the equatorial star chart, there is a wavy line you may recognize as similar to a sine wave. This is the apparent path of the Sun relative to the stars, also called the ecliptic. The Sun isn’t really moving, this apparent path is due to the Earth orbiting the Sun. You can look up the dates of the equinoxes and solstices. You should be able to guess the coordinates for the Vernal Equinox.

( /4) 8: What are the R.A. and DEC for the Sun at the following times of the year?

 R.A. DEC Summer Solstice Vernal Equinox Winter Solstice Autumnal Equinox

(+ /4) BONUS QUESTION: Imagine that you have crash-landed on a planet orbiting the near-by star Alpha Centauri A. Where (R.A.?, DEC ? ) would you look in the alien night sky to find home (i.e., our own star the Sun and solar system) if you only knew that the Alpha Centauri A position in the earth sky (i.e., as seen from earth) is R.A. 14 hr 39 min, DEC – 60deg 50 min? Assume most star positions and constellations change relatively little in moving from the Earth to Alpha Centauri A (This is reasonable because Alpha Centarui is very close to use compared to most stars). HINT- Remember that

line-of-sight connecting the earth at the center of the celestial sphere and any star on the celestial sphere works both directions.

R.A. DEC

## PLANISPHERES/STAR WHEELS

One of the most convenient ways to find out which stars are going to be visible in your area at a given time of night in your area is to use a star wheel. By lining up a time and a day you can see which stars will be visible. Notice that a star may be visible at different times on different days.

· Find a star wheel, or use one you made from the Sky & Telescope activity at https://www.skyandtelescope.com/astronomy-resources/make-a-star-wheel/ . Your instructor may have you do this in class.

( /10) 9: For each of the times below list the constellation or constellations nearest the specified horizons.

1. Tonight at 9 PM

a. Southern Horizon?

b. Northern Horizon?

c. Eastern Horizon?

d. Western Horizon?

2. In one month, at 9 PM

a. Southern Horizon?

b. Northern Horizon?

c. Eastern Horizon?

d. Western Horizon?

3. On October 31st at 12am

a. Southern Horizon?

b. Northern Horizon?

c. Eastern Horizon?

d. Western Horizon?

4. On June 10th at 3 AM

a. Southern Horizon?

b. Northern Horizon?

c. Eastern Horizon?

d. Western Horizon?

## USING STAR CHARTS OR WHEELS TO FIND YOUR WAY AROUND THE SKY

( /30) 10: Carry out the observing instructions below and attach your results in the form of an observing log, as specified by your instructor. You will either do this in class or at home.

· Use a star chart or star wheel, as per your lab instructor. Don’t use an astronomy app for this activity. Use your red flashlight to look at the chart or wheel.

· If doing this lab at home, find a site that has as few urban lights as possible.

· Using just your eyes, pick a bright star that is fairly high in the sky. When choosing this star, make sure that there are other fairly bright stars nearby, as this will make navigation through the sky using the star charts easier.

· Now identify the bright star you chose by finding it on your star chart. (Use the patterns this star makes with its neighbors in the sky to identify the patterns on your star chart as the scale of the star charts may make identification tricky.) Make sure it isn’t a planet!

## Note: At some times of the year one or more planets may be visible. These will be very bright, won’t twinkle and will be near the ecliptic, but will not be on your star charts. Choose your navigation star carefully.

· Once you have satisfied yourself that you know where on your star chart you are, write down the name of the bright star you picked and give its R.A. and DEC.

· Start a sketch of the night sky and place your star on it with a label.

· By “hopping” from one star to the next, work way down to the EASTERN horizon, naming the stars you “visited” on your “journey”. Identify the constellation that is just rising. Include the stars and constellation on your sketch, and make sure to include the time.

· Find Polaris, the North Star. Start a new sketch with Polaris and the position of the Little Dipper and Big Dipper asterisms. Label the NORTHERN horizon.

· If you think you observed one or more planets, draw a rough sketch (using your star chart as guidance) of the portion of the sky where they were located. Give an approximate position for each (R.A. and DEC).

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