PHYS133 – Lab Observing the Sky
Goals: To observe the sky and report observations of different objects.
What You Turn In: The Data Sheets in the later portion of this lab.
Background Reading: Background reading can be found in Chapter 2 of your text and the background section of this lab manual.
Equipment provided by the lab:
• 6 inch Celestron Schmit‐Cassegrain reflector – Alt‐Az mount (See Figure 1) Powertank Case with eyepieces and filters Diagonal Make sure that the finders scope is attached. If not, ask your TA about attaching it.. Equipment provided by the student:
Pen Figure 1 - One of the main telescopes at the Gemini Observatory in Chile
Background: Humans have observed the sky longer than recorded history. Since ancient times we have created devices to help us measure and examine the sky. Many ancient civilizations constructed observatories that helped them to chart the positions of the “fixed” stars and the paths of the “wanderers”. This measurement was of great importance in many cultures.
For example, originally, the Egyptian calendar had 365 days and started in our month of July to correspond with the annual Nile River flood. The year was arranged in twelve months of thirty days each and an additional five days to fill out the solar year. But this had a problem. By observing and tracking the star Sirius (α Canis Major), it was found to have a year (i.e. return to the same position in the sky at the same time of day) of 365 and one quarter days. This was adopted as the ‘Sirius Year’ to keep the times of seasons and floods somewhat consistent with the calendar.
UDel Physics 1 of 10 Fall 2017 PHYS133 Lab Observing the Sky
The revolution in observing the sky came in the early 17th century, when Galileo Galilei first pointed a telescope skyward.
Figure 2- The earliest known illlustration of a telescope.
Figure 3 - Galileo's Telescopes
Galileo discovered that some objects in the sky were not points of light, but actually extended objects – they had a definite size. Venus showed phases similar to the moon, and Jupiter had moons going around it!
This kicked off an ever increasing size and innovation in optical observing. Larger refactors (lens) and Isaac Newton’s reflectors (mirrors) leading to today’s combination telescopes (catadioptric – e.g. schmidt-cassegrain).
Before You Start
Make sure you are dressed for being outdoors! You will be looking through various telescopes and record your observations.
Dim light observing with your eyes, which we will be doing, is impeded by alcohol, nicotine and low blood sugar. So, it would be best to have eaten, not had alcohol or smoked recently.
Procedure
General Observations
Since there are only a few telescopes, you will be sharing them with your colleagues.
There are several telescopes available for use.
Focal Length
The focal length (f ) of a lens is a unique characteristic of the lens or mirror. The focal length of a lens/mirror may be loosely defined as the distance from a lens/mirror at which a very distant object will produce an image.
The f-number of a lens is a measure of how bright an image the lens/mirror will produce. It is the ratio of the focal length to the diameter of the mirror (or lens). For example a f/6 10 cm diameter lens has a focal length of 60 cm.
A telescope’s magnification changes depending upon what eyepiece is used. The main purpose of a telescope is to collect and focus light from distant objects. Therefore, if you are purchasing a telescope, the main concern is the objective diameter and quality, as you can change eypieces to increase the magnification. NEVER by a telescope based upon its “magnification power”.
UDel Physics 2 of 10 Fall 2017 PHYS133 Lab Observing the Sky focal length of objective Magnification focal length of eyepiece
Make sure you answer the questions on the data sheets.
1. Once outside, you will learn to align the telescope using the remote on the side of the telescope. Make sure that the telescope is plugged into the Powertank and turned on and then walk through the alignment. ALIGNMENT IS THE TOUGHEST PART OF AMATEUR ASTRONOMY. It might take more than one try to get it right.
2. Press ENTER on the remote to begin alignment. Follow instructions for SKYALIGN.
a. The Latitude / Longitude of Newark, DE is 39° 41' 1" N / 75° 45' 0" W
b. Enter the current Date and Time and continue.
3. Aligning the telescope involves successively pointing the telescope at three bright objects using the arrow keys on the control pad. Do not move the telescope by hand! Any bright star will do, but select three objects that are far apart in the sky. Do not use the Moon. The screen should say Center Object 1.
4. Using the control pad, align the red dot of the star pointer with your first object.
5. Press ENTER.
6. The object should now be visible in the eyepiece. If you do not see the object in the eyepiece, slowly pan the sky with the control pad until it is visible. Use the control pad to center the object in the eyepiece.
If the object is centered in the eyepiece but not centered in the star pointer, use the steering knobs on the star pointer until it too is aligned. (See Figure below)
7. Press ALIGN.
8. The screen should say Center Object 2. Select a second object and repeat the above procedure.
9. The screen should say Center Object 3. Select a third object and repeat the above procedure.
UDel Physics 3 of 10 Fall 2017 PHYS133 Lab Observing the Sky 10. After a few seconds, the screen should say Match Confirmed. If so, press ENTER and proceed with your observations. If the screen says Align Failed, follow the onscreen instructions to repeat the process. Observations: 1. Your TA will help you identify objects of interest. You should view six or so objects tonight.
2. Begin with the Moon if possible.
3. Move onto any planets that happen to be visbile.
4. If the Orion Nebula is in the sky view this object. Otherwise, find an interesting nebula.
5. Observe a star cluster.
6. Observe a double star.
7. Observe a galaxy.
8. Once you have observed an object, make sure to draw it on your post lab report in as much detail as you can. If you view the moon, see if you can label any features. Remember that the telescope flips images left to right. (Why is that?)
UDel Physics 4 of 10 Fall 2017 PHYS133 Lab Observing the Sky
UDel Physics 5 of 10 Fall 2017 PHYS133 Lab Observing the Sky
Names: ______Section: ______
______Date: ______
TELESCOPES:
Name of Telescope
Type of Telescope
Type of Mount
Size of Objective
Focal length of Objective
1. What is the primary purpose of an astronomical telescope system?
2. What is an Alt-Azimuth mount?
3. What is an equitorial mount?
4. What is the magnification of a telescope with an objective focal length of 40 cm and an eyepiece of 26 mm?
UDel Physics 6 of 10 Fall 2017 PHYS133 Lab Observing the Sky 5. When trying to find a star in a telescope, a lower magnification is useful since it presents a larger field of view through the telescope. Using you knowledge from the equations given above, calculate the magnification given by the 40mm eyepiece and the 25mm eyepiece for an 6 inch Schmidt-Cassegrain telescope. The focal ratio of the telescope is f/10. (1 inch = 25.4mm)
Object #1:
Eyepiece used:
Any observations:
UDel Physics 7 of 10 Fall 2017 PHYS133 Lab Observing the Sky
Object #2:
Eyepiece used:
Any observations:
Object #3:
Eyepiece used:
Any observations:
UDel Physics 8 of 10 Fall 2017 PHYS133 Lab Observing the Sky Object #4:
Eyepiece used:
Any observations:
Object #5:
Eyepiece used:
Any observations:
UDel Physics 9 of 10 Fall 2017 PHYS133 Lab Observing the Sky
Object #6:
Eyepiece used:
Any observations:
6. Rank the planets you saw from brightest to dimmest.
7. If you observed the moon, which features can you identify from the figure in the manual? List here and label on your drawing above.
8. In which constellations can you see the planets? In that respect what do the planets have in common with the Sun and our Moon?
9. How does looking through a telescope change the orientation of objects (e.g the Moon)?
UDel Physics 10 of 10 Fall 2017