The Night Sky [Optional - only for those interested] by Michael Kran - Thursday, 2 October 2008, 03:49 PM

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1 The Night Sky [Optional - only for those interested] by Michael Kran - Thursday, 2 October 2008, 03:49 PM A question sometimes arises: "What's up in the sky at a particular moment?" There are several ways to go about answering this question. One answer is Sky Charts. There are representations of the sky using a particular time and latitude. They are excellent for visual viewing, and only OK for telescopic use. A good example of this type of viewing aid is here: The second page lists telescopic objects of interest for that month. Another approach is planetarium software. This requires that you enter in your location. It can be precise in terms of GPS coordinates, or it can just be a nearby city. Either is fine, even a few hundred miles off will not be significant for our purposes here. Remember in the case of remote telescopes this information is about the location of the telescope, not the city where you are using your computer. Next, you have to select the time you will use the telescope. If your reservation is for the following Thursday at 10:00 PM Mountain time, then you want to see the sky on that Thursday with the local time of the observatory. What matters the location and local time where the telescope is located. Stellarium is an example of a free piece of software in this category. And it runs on both the Mac and PC.

2 A third approach is what is called "session planning software". For the PC, an example of such software is aptly named "What's Up?". Here, as with the planetarium software you need to enter in the location of the telescope and the GMT deviation -- which really just means "TIme Zone". Make it easy, just click "Set Your Location" and pick Albuquerque, N.M. It's close enough for our purposes here. The time zone for New Mexico, during Daylight Saving, is 6 hours behind Greenwich Mean Time. Otherwise, it is -7 GMT. The benefit of using something like What's Up is that it answers the question like: "What galaxies (Nebula, Planetary Nebula, Globular Cluster, and/or Open Cluster) is up in the sky on a particular night at a particular time. It also answers questions such as: "What is the apparent size of that object? " The results page is sortable by any of the listed characteristics of the object. The last feature, of being about to display and sort on the size of the object is quite useful if you are matching the apparent object size to the field of view of the telescope (often abbreviated "FOV"). Matching the FOV of view of the telescope and the apparent size of the object are key to good composition.

3 The Apparent Size of an Object by Michael Kran - Thursday, 2 October 2008, 04:14 PM Here is What's Up. A free PC program designed to tell you what is up in the night sky at a particular location and time. I have selected a location New Mexico by pressing the "Set Your Location" button and selecting Albuquerque, New Mexico. I know that daylight saving is being observed in New Mexico, and that the GMT deviation is -6. I then click "Save Defaults" so that information is stored for the next session. Next, entered the date, 10/9/2008 and time using a 24-hour clock, 22:00:00 or (10 PM). Lastly, I have selected a one hour observing window by entering "1" in the Session Length (hrs) field. You can choose what types of objects to look for. In this example, I am looking for galaxies. Optionally, you can click on the fourth column titled "Size" so it would sort all the galaxies by apparent size. I have not done this here. You are seeing the default screen. Sorting by size is a quick and useful way to match the apparent size of the object with the field of view of the telescope. We will cover that subject next.

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5 Matching telescope FOV to apparent size of object by Michael Kran - Thursday, 2 October 2008, 04:40 PM The apparent size information in "What's Up" would be more valuable, if we just knew the telescopes' fields of view. The easiest way to share this information is in table format. Telescope FOV (in arc minutes) AP180 = FOV 24' x 32' Epsilon 180 = FOV 60' x 80' [about 6 time greater area than the AP180] FSQ-106 = FOV 155' x 234' [about 50 time greater area than the AP180] Now, you can see the relationship between the object's apparent size and the angular size of telescope FOV. I have inserted the What's Up screen again. But this time, I have clicked the top of the fourth column. I have sorted the objects listed by apparent size. Immediately you can draw some conclusions. If you wish to image M31, the Andromeda Galaxy, the only telescope you have available that is up to the task is the FSQ-106. The reason is Andromeda, our closest galaxy, takes up an enormous about of sky. It is about two-and-a-half degrees on the long axis. We spoke in class about how one's fingers and hand relate to angular size. If the width of one finger is about 1 degree, then Andromeda is over two fingers' width. That might sound

6 like much but consider the following: The moon's apparent size from earth is only half a degree (30 arc minutes). Andromeda has an apparent size 5 times as large on the long axis. Actually Andromeda, like our own galaxy, the Milky Way, is roughly a flat disk. Andromeda has the shape it does because the galactic disk is tilted. Andromeda falls in the middle between edge-on and face-on galaxies. Now that we have studied angular dimensions and the distance formula we know that Andromeda must be much, much bigger than the moon to be farther away and have a greater apparent size as well. We can save that for discussion for another time. Suffice to say, the moon is a little over 2000 miles across. And Andromeda is in excess of 100,000 light years across. If, on the other hand, we wished to image NGC 0891, which is an edgeon spiral galaxy, the FSQ-106 won't be the right telescope. NGC 0891 is about 12 arc minutes across. It would be swimming in a FOV of 155' x 234'. However, it might look about right in the FOV of either other telescope. This extra step of matching the telescope FOV to the apparent size of an object is key to a well-composed image.

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8 Previewing how an object will look by Michael Kran - Thursday, 2 October 2008, 07:36 PM Sometimes it helps to see how an object might look before you image it. There are different ways to approach this. You could find it on the web. For example, a search in Google Images usually works. If you'd like an image along with some background information both seds.org and Wikipedia are good resources. For example, if one were looking for information on M31, The Andromeda Galaxy, here are two links: While the above approach helps you see what the object looks like, it can't help you envision how it will look if you take an image of it. Here's where another approach shows his strength. For PC's, there is a free program called the "CCD Calculator" which includes a collection of images taken by amateurs, along with the ability to select a telescope and CCD camera from a drop down menu. By good fortune, all three of the equipment combinations at Tzec Maun are available from a drop down menu inside the CCD Calculator. Just to recap. The principle behind the CCD Calculator is to take a collection of images and to show you how they might look through different telescopes and different cameras. Because many of the objects you may want to image are in the library of images, and all three telescope configurations can be selected from a drop down menu, with

9 very little effort you will have a good idea what the final result should look like. Tzec Maun telescopes & what to select in CCD Calculator For the AP206, select the following Ron Wodaski's CCD Calculator: For the Telescope select: AP Starfire EDT 206 f/7.7 For the Camera select: SBIG Rsrch 6303E/LE For the Epsilon 180: For the Telescope select: Takahashi Epsilon 180 For the Camera select: SBIG ST-2000M/XCM For the FSQ : For the Telescope select: Takahashi FSQ-106 For the Camera select: SBIG ST-2000M/XCM The program can be downloaded here: Below is an example of what the configuration screen looks like for the FSQ-106. There are only three things that you need to be concerned with: 1. Pick the telescope, in this case, FSQ Pick the Camera, in this case, SBIG Rsrch 11000M/CM

10 3. Select the object to view, in this case, M031.jpg (i.e., Andromeda Galaxy).

11 Website with sample RGB images to combine in SalsaJ by Michael Kran - Thursday, 2 October 2008, 08:18 PM If you would like combining images in SalsaJ, and excellent source of sample images is the amateur Jim Misti's website. Here Jim Misti has taken eight common objects in the night sky, and provided the separate Red, Green and Blue FITS files. This is apropos as the images were taken with an FSQ-106 and SBIG STL-11000M, the identical equipment is available to you at Tzec Maun. It is worthwhile to look at the exposure times Jim used for these images. Jim has selected 5-minute sub-exposures for each color channel. However, unlike most of us, he has not stopped with just one image for each color. Rather he has taken from 4 to 13 images, each 5-minutes long, through each filter. Therefore, if the images you take are not quite up to Jim's standard, the first area for improvement will be to increase the number of exposures for each filter. Taking one image per filter is sufficient. Though if you wish, you may go for additional sub-exposures of the same color. These images do not have to be taken on the same evening. Publishable amateur astrophotography is typically the result of combining images from hours of imaging, sometimes collected over several nights. These are then stacked to produce one final image. To give you an example of what one user was able to do with Jim Misti's RGB images, take a look below. This is the result of an amateur, Andre Tamanti, combining and adjusting the separate R, G and B FITS files provided on his website. It worth recalling the final image represents a total of 2 hours of imaging, using 5-minute sub-

12 exposures.