The Celestial Sphere Diagram Understanding The Celestial Sphere Diagram for New York State (from RegentsEarth.com)

This is a ‘celestial sphere’ diagram for NEW YORK STATE This is a ‘celestial sphere’ diagram for NEW YORK STATE. There are a few basics you need to know in order to learn how to interpret what you see. First, this is you, X the observer. You are standing in the middle of a field with the sky above you. Directions (N,S,E,W) are marked.

60o The protractor indicates “altitude” above the horizon. The horizon is the circle (field) in which you are standing. The altitude is the angle formed between the horizon and a line drawn to an object in the sky. For instance. Suppose the Sun was here. What is its altitude? The altitude, measured in degrees, is the angle between a line drawn to the Sun...... and the horizon..... That angle is..... Now that you know what altitude is and that it’s measured in degrees it’s much easier to just read the altitude using the protractor. 60o

We need to learn the daily path of the Sun on each of the four ‘special’ days of the year: The solstices, 6/21 and 12/21, and the equinoxes, 3/21 and 9/21. Let’s start with the summer solstice, June 21st. The Sun always rises in the east but on 6/21 it rises north of east. It rises higher and higher in the sky.... until it’s touching this line..... Whenever the Sun touches this line it’s solar noon, the time of day when the Sun has reached its maximum altitude. Every point on this line is some time in the morning, the AM, before noon! 6/21

You might be asked “what is the altitude of the Sun at noon on June 21st?” Easy! You know that this is the path for 6/21. You know that when the Sun touches this line, it’s solar noon. So just read the noon altitude from the protractor. The noon altitude of the Sun on June 21st is more than 72o but less than 76o. 6/21

OK, more than 72o but less than 76o, but what is it exactly? First of all, if this is a multiple choice question there will be only one answer that’s even close. Choose that one. But if you must write a response remember The noon altitude will vary within the state depending on your latitude. That means there is no ‘absolutely correct’ answer. An answer such as 73o or 75o degrees will be perfectly acceptable. 6/21

OK, what’s next? Easy. What happens after noon? The Sun starts to set (go down). Every point on this line is afternoon (PM). And please notice (this is important!), if the Sun rose NORTH of east it will set NORTH of west! 6/21

Next, the equinoxes. Since the path of the Sun is the same for both 3/31 and 9/21, think of it as two for the price of one! On the equinoxes the sun rises exactly due east and it sets exactly due west. This is true everywhere on Earth! It rises higher and higher.......... until it reaches its solar noon position of about 50o. Remember, the exact solar noon position depends on latitude. Then, after noon the Sun sets exactly due west! As before, every point on this line is a time in the morning. and every point on this line is a time in the afternoon.

Lastly, the Sun’s path on the winter solstice, December 21st: The Sun rises south of east....... It rises higher and higher to its noon position. At noon on 12/21 the Sun’s altitude is about 25o. After noon the Sun gets lower and lower until it sets south of west. And of course...... and afternoon. morning

SOUTH Here’s a common regents question: Remember, you are here! In which direction must an observer (you) face to see the Sun at noon? Answer: The Sun is going to be here or here or somewhere in between (depending on the date). So no matter what the date, to see the Sun at noon an observer in New York State would always look in this direction...... towards the......................... SOUTH

The Sun is NEVER directly overhead in New York State! Another common regents question: For how many days a year is the Sun directly overhead at noon in New York State? The Sun might be here or the Sun might be here or somewhere in between. But for the Sun to be ‘directly overhead’ it would have to be here and it NEVER is! The Sun is NEVER directly overhead in New York State!

Try this: Draw a small sun where it would appear at 3PM on June 21st. First, which is the June 21st path? Remember, June 21st is the ‘longest day’ so the longest day has the longest path. Now, where on the path is 3PM? The Sun rises in the east so this line is morning and this line is afternoon 3PM would be the middle of the afternoon so draw your sun here 6/21

One more. Draw a small sun as it would appear at 8AM on March 21st. First find the March 21st path. Since 3/21 is an equinox it must be the middle path. OK, now find which part of that line is ‘morning’ (Sun rises in the east). 8AM is fairly early so put the sun low on the line near where it rises. Pretty easy!!

Now let’s try drawing some shadows. They love shadows on the regents. OK, there’s a pole stuck in the ground in the center of the field. Draw the shadow of that pole at noon on December 21st. Find the noon position of the sun on 12/21 (Hint: Shortest day = shortest path and noon is where the path of the Sun touches the protractor) Using a straight edge (a ruler) draw a line from the Sun’s position past the top of the pole all the way to the ground (dashed line). BE CAREFUL and ACCURATE! The shadow is on the side of the pole opposite the Sun. It runs from the base of the pole to the tip of the line. Using a straight edge carefully and accurately draw the shadow. DONE!

One more shadow, please. Draw the shadow of the pole at 3PM on June 21st. First find the 6/21 path (Hint: longest day = longest path) Since 3PM is after noon, find the part of the path that’s afternoon. Since 3PM is the middle of the afternoon, locate the position of the Sun in the middle of the afternoon line. Using a straight edge, carefully and accurately draw a line from the Sun, past the top of the pole to the ground. You can’t be exactly sure where the line should end so make a best guess at some point on the side of the pole opposite the Sun. DONE! Again using a straight edge draw the shadow from the base of the pole to the end of the line.

Lets sum up...................What must you know and what must you be able to do in order to be ready for a test or for the regents exam? > You absolutely must be able to accurately draw the path of the Sun on the 4 important days of the year, solstices and equinoxes. 4 dates, 3 paths. This means knowing..... > Where each path begins and ends > The proper altitude for the noon sun for each path The ONLY way to do this is to get blank celestial sphere diagrams (many) and practice drawing the paths until you can do it perfectly in your sleep (click here) > Know that in NYS the Sun is always in the southern sky at noon. > Know that in NYS the Sun is never directly overhead at noon. > Know where to draw a ‘sun symbol’ for any date and time specified > Know how to draw the shadow of a pole for any date and time specified and understand that this is just a starting point. Celestial sphere diagrams can be drawn for any location on Earth with the Sun’s path for any date during the year. There are far too many possibilities for anyone to memorize. Instead each situation can be ‘figured out’ if you understand the basic facts of ‘Earth’s Motions’. Done!

For practice print as many copies of this slide as you need For practice print as many copies of this slide as you need. Draw the paths from memory until you can do it with no errors.......twice!