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MESSIER OBJECTS Introduction Charles Messier lived in France from 1730 to 1817. An avid comet hunter, he noticed a fuzzy patch in the sky with his telescope during August 1758. Thinking he had spotted a comet, he kept watch on this region of nebulosity and noticed that it did not move relative to the background stars. If it had been a comet, it would have shown more motion, since comets being objects within our solar system move at a rate similar to planets. Not wanting to make the same mistake again, Messier noted the position of this strange object in his catalog as M1. Over the next few years, Messier came across other similar nebulous regions that were not comets and his list of objects not to be mistaken for comets grew. He published his first list of 45 such confusing objects in 1774. Others in the field added to Messier’s list, including a contemporary named Pierrre Mechain. By 1781, there were 103 objects in this list and historians added another seven which they found described in notes left by Messier and Mechain. Today, this list of 110 objects are collectively called the Messier objects, or the M-objects. But what were these fuzzy patches? As telescopes improved, better resolving power yielded the details of these nebulous regions. Rather than being comets they are far more important to astronomy than the icy snowballs Messier was trying to discover. M1 the first object is none other than the Crab Nebula which was the site of the supernova explosion that occurred in 1054 AD. Messier was viewing the remains of that gigantic explosion, and photographs of this region clearly show the expanding gas cloud. Some of the other M objects are galaxies, globular clusters, open clusters, or stellar nurseries. In 1888 J. L. E. Dryer published the New General Catalogue which was a more extensive list than Messier’s. Objects listed by Dryer have the prefix NGC. Many objects will therefore have M names and NGC names. And like the stars, some objects will also have descriptive common names like the Sombrero Galaxy and the Ring Nebula which reflect what they actually look like. You will use Stellarium to identify some of these objects and find details about them. And since you have studied the life cycle of stars you will see some of the stages, since Stellarium will allow you to zoom in as if you were actually using a telescope with steadily increasing magnification. You will also see more distant objects like other galaxies which will prepare you for the next topics in the course. Equipment Stellarium Program. Exercise Steps to be done on the computer are in alphabetic order (A, B, …) and questions to be answered are in numeric (1, 2, …) order. A. Launch Stellarium program.

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The instructions for this lab have been written using Stellarium version 16.1 Stellarium now has a new version 17.0 But we recommend using version 16.1 just to be safe. So the links to download versions of Stellarium 16.1 are as follows:

Win 32 v 16.1: win32.exe

Win 64 v16.1: win64.exe

Mac v16.1 :

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B. Your viewing location should be set as Dallas. If you did not do the “Zodiac & other Constellations” lab then you must set up Stellarium properly. Please follow setup steps A through E in the “Zodiac & other Constellations” lab and then continue with this lab. C. When you click on the lower left corner of the screen you should see two menu bars in an L-shape. If you click on the two arrows, one facing up and the other facing right, the arrows turn into squares and the menu bars will remain on the screen. Press the number 7 button to stop time in Stellarium. The second icon from the top on the vertical tool bar sets time and date. Set it to Aug 1 of the current year at 9:00 pm (21:00:00). Close the date and time window. D. Experiment with the “Page Up” and the “Page Down” buttons. This allows your screen view to zoom in and zoom out. Keep the view as you first saw it. E. Click on the 3rd icon from the top of the vertical tool bar, which is “Sky and Viewing options window.” Click on the DSO tab at the top of the window. DSO stands for deep sky objects, signifying that the objects you are about to see are only visible with telescopes in dark sky conditions. Check M and NGC, Check Filter by Type and ensure that all items in the Filter by Type box are checked. Check Labels and Markers and keep the labels slider a bit to the left of middle. Now click on the MARKINGS tab and in the “Celestial Sphere” window check cardinal points. Click on STARLORE tab and in the “Options” window check show labels, show lines with thickness, and show boundaries. Beside the show lines with thickness change the number to “2.” Next click on the LANDSCAPE tab, choose Ocean on left hand side, and uncheck all options. This will allow the screen to show objects that are below the horizon also so that you do not have to keep changing the date. Close the View window.

F. On the vertical tool bar click on the magnifying glass icon which brings up a “search” window, type NGC1952 in the box and press enter. The software will show the location of NGC1952 and put it in the center of the screen. However, when you look at the screen, you will see a large number of stars and other objects! How do you know which one is NGC1952? If you want to see what NGC1952 looks like close up use the ZOOM feature (page up key) to get a closer view. You will have to press the page up key many times until you see a color image of this object. G. Information about NGC1952 will also appear in the upper left part of the screen. This is also known as M1, take a few moments to read the details. It is the Crab Nebula and is the site of the supernova that exploded in 1054 AD. Its magnitude, RA, declination, azimuth, altitude, size, parallax and many other details are all given. H. Zoom out with the page down key, click on the magnifying glass icon, and type in M42. This is also called the Orion Nebula. Adjust the zoom to find the exact location of M42 in the Orion region.

1. In what part of Orion region does M42 lie? a. Near the star Betelgeuse b. In the region below the three belt stars c. Between Betelgeuse and Bellatrix d. Just south of Rigel

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2. What is the size of M42? a. 13 degrees b. 1.5 degrees x 1 degree

c. it is about the size of the full moon d. 15 h

3. What is M42? a. It is a planetary nebula b. It is an H-II region consisting of a giant cloud of gas c. It is a stellar nursery d. Both b & c are correct

J. Next look for M45. This is the familiar pattern called the Pleiades.

4. In which constellation does M45 lie? a. Taurus b. Auriga c. Perseus d. Orion

K. Zoom into M45 and see the many stars in the cluster called the Pleaides. Click on its brightest stars called Alcyone, Merope, Electra and Taygeta. Which one is the brightest?

5. Which one of the following is the brightest star in the Pleiades? a. Alcyone b. Merope c. Electra d. Taygeta

L. Go to M57. What type of an object is it?

6. M57 is a a. Galaxy b. Globular cluster c. HII region d. Planetary nebula

7. In what stage of stellar evolution is M57?

a. It is a stellar nursery where stars are being formed. b. Planets will be forming from the visible circular material c. The red giant phase is about to begin d. The parent star has ejected most of its material after its red giant phase M. Zoom out and look for M20 which is also called the Trifid Nebula. This is another star-forming region. Note the size of M20.

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8. Compare the sizes of the Trifid Nebula and Orion Nebula. Which one is bigger? (You recorded the size of M42 in question 2) a. Trifid b. M42 c. They are about the same d. It is not possible to tell from the screen

9. Zoom into the Trifid Nebula to note its color. What is its color?

a. Red b. Blue c. Both red and blue are visible d. Green

N. Next, zoom out and find M18 which is an open star cluster in Sagittarius. 10. What is the distance to M18?

a. 1.5 AU b. 1.5 kpc c. 1.5 pc d. 6.9 pc

11. What will be the distance to M18 in light-years? Look up the appropriate

conversion factors! a. 2.3 x 10-5 ly b. 5000 ly c. 5 ly d. 23 ly

12. Why are clusters important in astronomy?

a. Stars in a cluster were born from the same parent cloud. b. Stars in a cluster are all at similar distances from us c. Both a & b are valid d. Like the stars in a constellation, the stars in a cluster only appear to be close

together O. Zoom out and find M19 which is a globular cluster. Zoom in to see the similarity or difference between the open star cluster and the globular cluster. Also record the distance to M19. 13. Which cluster, open or globular, has more densely packed stars?

a. Open cluster b. Globular cluster c. Both contain about the same density of stars d. It depends on how far you zoom in

14. Which cluster, M18 or M19 is further away?

a. M18 b. M19 c. They are both at similar distance d. It depends on how far you zoom in

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P. The Sagittarius region is particularly rich in globular clusters which are denoted by small yellow circles with a cross. Zoom into the Sagittarius region and click on some globular clusters to determine their names and check what they look like and how far away they are.

15. Name at least two globular clusters found in Sagittarius and give their distances.

Q. In 1920 Harlow Shapley made a very important discovery related to globular clusters. Using a technique developed earlier by Henrietta Leavitt, he was able to measure the distances to many globular clusters and on mapping their 3-dimensional locations in space he found they outlined a giant sphere with its center towards Sagittarius. Also, the solar system was not located at the center of this sphere but about two-thirds away from the center. From these observations Shapley reached the bold conclusion that the globular clusters formed the outline of our galaxy and the center of the galaxy was in the direction of Sagittarius. This idea will form the basis of many ideas to be discussed later for our galaxy. R. Another mystery facing 20th century astronomers concerned some of the M-objects that were also fuzzy patches but they did not have a definite spherical shape shown by the globular clusters. Search for M31 which is our close neighbor, the Andromeda Galaxy. After you zoom in, look for two other galaxies in close proximity to M31. You should be able to find them on the same screen as M31.

16. Two other galaxies close to M31 are a. M32 and M110 b. M35 and M65 c. M44 and M104 d. M66 and M109

S. Under very clear dark skies, with pristine seeing conditions, you can actually see the blur of Andromeda with your naked eyes! Make a note of its size on the Stellarium screen. Also note the distance to M31.

17. Is the size of M31 more or less than M42? a. Larger b. Smaller c. Unable to judge since they are in different regions of the sky d. They are about the same

18. Which object, M31 (galaxy) or M19 (globular cluster) is further away?

a. M31 b. M19 c. Cannot tell since distances are not given in ly. d. Cannot tell since distances are given in different units

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19. In view of your answer to many of the above questions, which statement below best captures the relation between galaxies and globular clusters? a. Globular clusters lie inside our galaxy b. Andromeda Galaxy lies outside our galaxy c. Globular clusters outline our galaxy d. All statements are correct

T. Galaxies are classified as being spherical, elliptical, spiral or irregular. Search for M51, M101 and M104.

20. What type of a galaxy is M51? a. Spherical b. Elliptical c. Spiral d. Irregular

21. Write your impressions of M51, M101 and M104.

U. Use the onscreen data chart to record the distance and “redshift” for M51, M101 and M104 in the table below. Recall that redshift measures how far the spectral lines have shifted and it can be used to calculate the velocity (speed) of objects. The equation to convert redshift (denoted by z) into velocity (v) is v = cz where c = speed of light. For example, since M101 has redshift z = 0.000811, its velocity v = (3 x 108 m/s)x(0.000811) = 2.43 x 105 m/s

Galaxy Distance Redshift z Velocity v = cz

M101 6.4 Mpc 0.000811 2.43 x 105 m/s



22. Record your values of distance and velocity for M51 and M104.

23. In view of your answer to 22, if the galaxy’s distance increases, what happens to its velocity? You will pick up on this idea in the next chapter!

24. What did you learn from this lab?


Questions 1- 21 = 1 point each

Question 22 = 2 points

Question 23, 24 = 1 point each

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