Astronomy 3 Lab Manual Deep Sky Observing 1

Observing Deep Sky Objects

IntroductionThis lab involves using the Dartmouth’s Shattuck Observatory (a 9.5 inch refractor built in 1870),a modern 8 inch reflecting telescope and a portable 4.5inch Orion SkyQuest reflector (used in yourfirst nighttime observing lab). All of these telescopes are located on the hill behind Wilder Lab.You will use the Shattuck telescope (pictured below) to observe a planetary nebula (NGC 7662),the 8 inch reflector to observe a globular star cluster (M15), and the 4.5 inch telescope to observethe Andromeda galaxy (M31). All of these objects are located very far from the Earth, and aretypically called ‘deep sky’ objects. The distance to NGC 7662 is approximately 2000 pc, M15 is10,000 pc from the Earth and the Andromeda galaxy is currently at a distance of 770,000 pc.

Figure 1: Shattuck Observatory and the Dartmouth campus in 1904.

The observing part of this lab will take you a maximum of 30 minutes to complete. You must signup for a specific 30 minute time slot on Blackboard prior to coming to the lab. Observations willoccur between 8 – 9:30pm during the first week of November, and (if needed) between 7 – 8:30pmthe second week of November (after daylight savings time ends). An e-mail will be sent out by 5or 6pm to announce if the lab will occur that night. Go directly to the telescopes behind Wilderlab when it is time for you to make your observations. Hand in your answers to the pre-labquestions to the teaching assistant when you arrive at the telescopes. The teaching assistantswill have the telescopes set up and pointed at the different deep sky objects. Each student will takemake their own observations; you will not be working in partners in this lab.

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ObservationsYou’ll need four things to do the observing part of this lab: a flashlight, a notebook, a pen, and thislab description. You must READ THIS WHOLE HANDOUT before you do your observations.

Go to each of the telescopes (in any order) and view the Andromeda galaxy, M15 and NGC 7662.For each object, make a sketch of what you observe (using the attached sheets) and note the fol-lowing on your data sheet:

1. Size relative to the eyepiece field of view.

2. Color, if any.

3. Object features. For example, can you see individual stars in M15, or the central star in NGC7662?

In addition, ask the TA to tell you the field of view of the telescope, and note this number down onyour data sheet.

Have the TA sign your data sheet after you have completed each of your observations.

AnalysisQ1: Why couldn’t you see individual stars in the M31 galaxy even though you were using atelescope?

Q2: If one wanted to see things larger (and presumably clearer), why not just use a higher magni-fication eyepiece on the telescope?

Q3: Based upon your drawings, and the field of view of each telescope, estimate the diameters ofthe three objects you observed in arc-seconds.

Q4: Using your estimated angular diameters, calculate the physical diameters assuming the phys-ical distance of:

• NGC 7662: 2.0×103 pc

• M15: 1.0×104 pc

• M31: 7.7×105 pc

Do these calculated sizes make sense?

Q5: Calculate the apparent magnitude of the central star in NGC 7662 assuming that it is a hotwhite dwarf with an absolute magnitude of M = +10. Does this explain why you did or did notsee it in the telescope?

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Q6: Suppose a Type Ia supernova with an absolute magnitude of M = −19 mag went off in theM31 Andromeda galaxy. Could we see it with our naked eye?

Q7: The Doppler shift of the M31 galaxy shows a blue shift meaning it is approaching us at aspeed of 300. km/s. How long will it be before it hits the Milky Way?

Writing up the LabLab reports are due 1 week after you complete the lab. Lab reports are to be put into the boxlabeled with your TA’s name next to the student mailboxes, which are located to the left of themain stairs when you enter Wilder Lab.

Make sure you follow all of the general guidelines for A3 lab reports, which are discussed in aseparate document posted onto Blackboard. Aside from the data sheet, you should use completesentences throughout your lab report. When answering questions, please do so in an essay style,referencing the question you are answering. When you have equations to solve, show all of yourwork (not just the answer), and include units if needed. Make sure you show all details of yourcalculations, and describe how you obtained your results.

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Pre-Lab Questions

You must answer the following questions before you come to lab. Hand in your answers to theTA at the start of the lab.

The answer to all these questions can be found in your textbook and the lab itself. The pre-labquestions will account for 20% of your lab grade. By reading the lab and thinking about it inadvance of performing the lab, you will find that the lab makes much more sense when you startcollecting data.

1. What is a planetary nebula?

2. What is a globular cluster?

3. If an object has an angular diameter of 10. arc-minutes and is located 1.0×104 pc from theEarth, what is its physical diameter in pc?

4. If a star is similar to the Sun and has an absolute magnitude of M = +5.0mag and is located350 pc from the Earth, what would be its apparent magnitude?

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Observer: Object Name:

Date: Time:

Sky Condition:

Telescope: Field of View:

TA Signature:

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Observer: Object Name:

Date: Time:

Sky Condition:

Telescope: Field of View:

TA Signature:

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Observer: Object Name:

Date: Time:

Sky Condition:

Telescope: Field of View:

TA Signature: