A Guide to the Stars
Introduction
In this lab you will learn how to star gaze using a Star Wheel, a Sky Atlas, and the free program Stellarium. (The links to the products are for reference only, no need to purchase or download anything for class.)
Important! Only use the Star Wheel to answer Part I questions, and only use the Sky Atlas to answer Part II questions, and only use Stellarium to answer Part III questions!
Part 1: The Star Wheel
The Star Wheel is a great tool for naked-eye star gazing. It shows you only the brightest objects in the sky, and allows you to easily determine which objects are currently visible.
Let's look at its parts:
At the top right, notice this star wheel is "Exact for 40˚ North Latitude". This means you can use this star wheel in cities like Denver, San Francisco, Cedar Rapids, and Salt Lake City. If you want to purchase a Star Wheel for a niece or nephew who lives in Texas, make sure you get one for their latitude!
The next part is the time part. What time is it right now?
Now locate the current time on the inside edge of star wheel, the part labeled with white text over the green paper, (which is also shown between the blue circles in the image below). Daylight Saving Time, also called Summer Time, runs from March through November.
Next you need to select the day - What month and day is it today?
Locate today's date on the date selector - the outer dark blue ring, and rotate the outer dark blue date ring until the "date tick" lines up with the "current time tick". The date ring is also located between the blue rings in the image below for reference.
Congratulations, you have set the star wheel to show you what the sky looks like right now! Take a moment to look at the constellations that are currently visible.
Polaris and your Zenith
The "North Star", Polaris, is located where the rivet that holds the two rings together is. Locate it meow!
Rotate the wheel one hour ahead, and one hour behind the current time, and notice how as you rotate, today's date slides across the time ring, and all the stars rotate around the North Star (the rivet)!
This allows you to tell which constellations have just risen, and which ones are about to set. You can also plan for star gazing during the day before it gets dark, because this tool allows you to predict the future! You're a Wizard, Harry! Great for stargazing party planning.
But pay close attention! This is NOT the center of the sky! It is off-center! This is because the North Star is not directly overhead at our latitude! (Though it would be if you were at the North Pole: Quickly discuss why!)
The center of this map (the map is the blue oval with the stars on it), anyway the center of the map is your Zenith! The Zenith is the point directly over your head when you look straight up. Look up! That's *your* Zenith! It's relative to your location, not an absolute position.
If you went outside and looked up right now, what constellation would be directly above you, at your zenith?
To use the Star Wheel, you hold it up over your head, and line up the cardinal directions: Place the North edge of the Star Wheel North, South to South, East to East, and so on.
The perimeter of the blue oval is the horizon - or the ground. You can think of it as a dome, or a bowl. The orange line in the image below is the edge of the earth, and the stars behind that green perimeter have are behind the earth!
The following image should help you visualize how the star wheel works - the perimeter is the entire horizon - the ground, 360 degrees around you. So you have to use your mind to imagine the star wheel as a bowl over your head - where constellations near the edge are near the ground, and constellations near the center are directly overhead.
Note the locations of Polaris in both images, as well as the lines of Right Asension which point down towards the earth, and the lines of declination which run circles around the sky.
Stellar Magnitudes
Located at the lower left of the Star Wheel is the legend for the star labels. The brightness of a star is called its Magnitude, and the humans can see stars in general with about magnitude 6 and lower. The Sun has magnitude -26. Yes, negative 26! The scale is weird, I know.
But for short hand, the Star Wheel puts spikes on the brightest stars. So when you are out star gazing, the spikey stars will be easiest to spot, which will help you navigate and find constellations.
Messier Objects
The last thing to mention is that the Star Wheel also contains so-called Messier Objects.
Charles Messier was an astronomer who catalogued 110 objects, originally published in 1771. Each object starts with an M.
For example, the Andromeda Galaxy is M31.
This was before galaxies were known to exist outside our own Galaxy! Charles Messier wanted to get famous by discovering comets, but these fuzzy objects were tricking him - so he decided to compile a list of known objects that appeared to be comets but were not. These are the Messier Objects, and they are a hodge podge of star clusters, galaxies, nebulae, supernova remnents
And now you can answer the questions in Part 1 of your lab manual!
Part 2: The Sky Atlas
The Pocket Sky Atlas is a book containing detailed maps of the stars.
Since the Star Wheel contains all of the objects you can see with the naked-eye, you would primarily use the Pocket Sky Atlas for stargazing with a telescope or a pair of binoculars.
Inside this book, you can see that each page is a section of the sky.
10 of these pages cover a slice of the sky from top to bottom. You can see in the following image, the whole sky is divided into 8 slice - and those 8 slices are further divided into 10 sections - so there are 10 pages per section.
As you turn the pages within the group of 10 sections, you are moving down the sky! This allows you to covere the whole sky in a single book.
The inside of the back cover (shown below) of the Sky Atlas gives you an overview of which charts cover which parts of the sky. Compare what you see here with the constellations on the Star Wheel.
The Table of Contents of the Sky Atlas are a little bit different - the contents of this book are arranged by Best Viewing Time. This makes this tool a quick and useful guide for planning what constellations and other objects to look for at any given time.
Note that the charts span the 'longitude' of the sky: Right Ascension, or R.A. The first 1-10 charts cover R.A. 0 hours to 3 hours. Compare these charts, 1-10, with the sky between 0h and 3 h on the star wheel. (The star wheel does indeed have pie slices, and R.A. labeled!)
The beginning of every 10 charts has an overview page as shown below.
Note the information: The R.A. range, the best viewing times (the bold one is the BEST of the best), and which pages those cover and the overview of the sky.
In the beginning of the Sky Atlas, there is a section with shortcuts to the locations of Constellations, as shown below:
The following image shows how the 10 charts are related to each other. This picture contains the first 3 charts, and you can see how chart 1 sits 'above' charts 2 and 3. Compare the lines of Right Ascension if you don't believe me! They are labeled in the inset image. Discuss this with your partner.
Now you are ready to answer the questions in your lab book!
Part 3: Stellarium
Stellarium is an open source - which means free! - application that is available on Mac, PC, and Linux.
To open it, click on the magnifying glass icon on the top right of your desktop to search for applications, and type Stellarium into the dialog box that pops up, as shown below:
When you first open Stellarium, it should set itself to the current day and time and location at Cedar Rapids, Iowa. You can verify this by looking at the very bottom of the screen.
You can adjust many settings with this software by accessing two menu bars.
They are hidden - one to the left and one along the bottom.
To access them, simply bring your mouse to the edge of the screen as shown below:
Try and toggle every button and go into every menu - what does pressing each button do?
Have fun!