27 September 2007

It was cloudy last night so I stayed home and put new index tabs in my Moon Observer’s Guide (and now the pages stick together where adhesive is stuck to them from the old tabs) and Pocket Sky Atlas. While thumbing through the text material at the front of Pocket Sky Atlas I came across this chart suggesting the best times to view the stars in different areas of the sky.

Best Viewing Times
R.A. Range	Evening	Midnight	Morning	Charts
0h to 3h	Nov./Dec.	Oct.	Aug./Sep.	1-10
3h to 6h	Jan.	Nov./Dec.	Oct.	11-20
6h to 9h	Feb./Mar.	Jan.	Nov./Dec.	21-30
9h to 12h	Apr.	Feb./Mar.	Jan.	31-40
12h to 15h	May/June	Apr.	Feb./Mar.	41-50
15h to 18h	July	May/June	Apr.	51-60
18h to 21h	Aug./Sep.	July	May/June	61-70
21h to 0h	Oct.	Aug./Sep.	July	71-80

It looks like dates listed with a slash are predicting good observing at the end of the first month and the beginning of the second while those with only one month are for the middle of that month but they don’t tell you that.

They don’t specify what constitutes Evening and Morning. I assumed that the listed dates corresponded with the time of the year when that particular piece of sky was in the south and the constellations would be the highest in the sky and viewable without distortion (I read that part about distortion in a book or heard it on a tape but have never experienced a noticeable distortion in the shape of a constellation, just its rotation as it floats across the sky.). I got out the Clié and fired up Planetarium . I set the date for 1Sep07 and went to R.A 20h30m, which is the center of the last R.A. range at the only time I was certain of (midnight) on the chart. Sure enough I was looking south. I repeated the process for midnight on 15Jan07 and R.A. 7h30m and was again looking south. As a last check I tried 15Jul07 at 2100 EDT (I bet the chart works best for Standard Time but there are no explanatory notes for that either and the rotation of the sky wouldn’t be that significant anyway.) and was again looking south.

Looking south from TotL is looking into the gegenschein rising from Citicorp and the Bloomberg building. We spend most of our time looking NNE (Manhattan N), so I revised the chart to indicate what would be in the NE between sunset and curfew. Then I decided that I needed a guide for what to look for in those parts of the sky so added in the Interesting objects to observe lists from the back of Observing With a Telescope.

Best Viewing Times Looking NE from TotL
R.A. Range	2100	2400	Objects
0h to 3h	Aug/Sep	Jul	M: 31 32 33 34 74 76 77 03 NGC: 40 55 104 147 185 188 247 153 362 404 457 663 752 869/884 891 1097 7814 SMC
3h to 6h	Nov/Dec	Aug/Sep	M: 1 36 37 38 42 45 79 NGC: 1261 1300 1360 1365 1501 1514 1535 1647 1851 1981 2070 IC: 405 LMC
6h to 9h	Nov/Dec	Oct	M: 11 25 35 41 44 46 48 67 81 82 NGC: 2002 2244 2261 2264 2281 2301 2353 2360 2362 2392 2403 2419 2440 2451 2477 2506 2516 3242 IC: 443 Abell 212
9h to 12h	Jan	Nov/Dec	M: 59 60 64 65 66 97 105 108 NGC: 2808 2841 2903 2997 3115 3132 3172 3195 3201 3344 3552 3628 3766 IC: 2602
12h to 15h	Feb/Mar	Jan	M: 3 49 51 53 61 63 68 83 86 94 98 99 100 101 104 106 NGC: 4216 4361 4372 4406 4449 4656 4755 4833 4945 5053 5102 5128 5139 5248 5286
15h to 18h	Apr	Feb/Mar	M: 4 5 6 7 10 12 13 14 18 19 21 23 26 80 92 NGC: 5823 5897 5907 5986 6124 6231 6302 6304 6337 6369 6388 6397 6441 6445 6532 5641 6543 6572 6633
18h to 21h	May/Jun	Apr	M: 8 15 16 17 20 22 27 56 57 65 71 NGC: 6210 6712 6752 6822 6826 6905 6934 6960/6092 7009
21h to 0h	Jul	May/Jun	M: 2 30 39 52 NGC: 731 778 7009 7023 7243 7293 7510 7635 7662 IC: 1396 5146

After the NNE-NE we look next in order of frequency to the SE (Manhattan E). So I changed the dates in the chart for that direction.

Best Viewing Times Looking SE from TotL
R.A. Range	2100	2400	Objects
0h to 3h	Seo/Oct	Aug	M: 31 32 33 34 74 76 77 03 NGC: 40 55 104 147 185 188 247 153 362 404 457 663 752 869/884 891 1097 7814 SMC
3h to 6h	Nov	Sep/Oct	M: 1 36 37 38 42 45 79 NGC: 1261 1300 1360 1365 1501 1514 1535 1647 1851 1981 2070 IC: 405 LMC
6h to 9h	Dec/Jan	Nov	M: 11 25 35 41 44 46 48 67 81 82 NGC: 2002 2244 2261 2264 2281 2301 2353 2360 2362 2392 2403 2419 2440 2451 2477 2506 2516 3242 IC: 443 Abell 212
9h to 12h	Feb	Dec/Jan	M: 59 60 64 65 66 97 105 108 NGC: 2808 2841 2903 2997 3115 3132 3172 3195 3201 3344 3552 3628 3766 IC: 2602
12h to 15h	Mar/Apr	Feb	M: 3 49 51 53 61 63 68 83 86 94 98 99 100 101 104 106 NGC: 4216 4361 4372 4406 4449 4656 4755 4833 4945 5053 5102 5128 5139 5248 5286
15h to 18h	May	Mar/Apr	M: 4 5 6 7 10 12 13 14 18 19 21 23 26 80 92 NGC: 5823 5897 5907 5986 6124 6231 6302 6304 6337 6369 6388 6397 6441 6445 6532 5641 6543 6572 6633
18h to 21h	Jun/Jul	May	M: 8 15 16 17 20 22 27 56 57 65 71 NGC: 6210 6712 6752 6822 6826 6905 6934 6960/6092 7009
21h to 0h	Aug	Jun/Jul	M: 2 30 39 52 NGC: 731 778 7009 7023 7243 7293 7510 7635 7662 IC: 1396 5146

The list of objects was developed for all sizes of telescopes so some of the objects on it are too faint for me to see with my optics.

While adding the objects, which came from lists of objects sorted by category and then be declination, I was struck by how frequently I was returning to one or two R.A. ranges for a particular type of object and that got me to thinking about them geospatially and resulted in the following map of the sky with the various objects plotted.

This is an incomplete analysis of the heavens because it is based on a list of objects that someone else thought were important for me to look at and I don’t know if they are a representative sampling of the density of all those objects across the sky.

First I found that the map was backwards from the way the constellations pass across the sky so I had to change the R.A. values to negative numbers to get 0h on the right where it belongs.

Looking at the distribution of clusters I found that

• the open clusters were primarily centered between 0h and 9h while the globular clusters were in a loose cluster of clusters (the opposite of what we observe in an individual globular cluster as they are almost always small and more dense than opens) between 12h and 21h.
• Galaxies occupy the areas between the globular and open clusters forming a sort of wall separating them from each other.
• Nebulae form a broad smile and are most concentrated at the corners of the mouth between from R.A. 15h to 0h and around to 9h.

The smile shape that was clearly evident when the clusters and nebulae were observed together reminded me of the Milky Way so I got out Pocket Sky Atlas and measured the location of the Ecliptic and Milky Way and added them to the chart.

To appreciate this chart you really need to look at the full size version.

Here I found that

• almost all of the clusters fall within the Milky Way
• the galaxy walls are beneath the peaks and above the valleys of the Milky Way, only a few appear behind the Milky Way, and always in the less dense portions of the Milky Way.
• all nebulae and most planetary nebulae are within the Milky Way
• the few supernova remnants that were listed all fall within the core of the Milky Way