The Oakland Astronomy Club Logo

Contents



A monthly publication of The Oakland Astronomy Club - A member society of the  
Astronomical League Logo

ASTRONOMICAL LEAGUE

This website created by
Kevin M. Berg

   

Featured Article

Knowing the Night Sky

By Kevin Berg

This is just a little commentary on the use of GoTo scopes versus manual slewing and the use of star charts and computer software, to assist one in knowing the night sky.

As a first scope, I've had an ETX-90/EC since March 1999, and it has proven to be one of the best purchases I have ever made for both portability and viewing (given MY expectations from its aperture). Of course, both the technical and non-technical support provided by web sites such as Mike Weasner's Mighty ETX Site has made it an even better purchase. In fact, I have been so satisfied by the scope's performance, the support and information offered by Mike's site, and the hobby in general that I have purchased an Orion SkyQuest XT10 (10" Dobsonian) to hunt down those fainter deep sky objects.

As most of you may know, a Dobsonian is an excellent choice of scope for viewing deep sky objects in particular. And you also may know that Dobsonian scopes don't include GoTo capabilities like the infamous ETX/Autostar combo, although manual GoTo devices using encoders (i.e., digital setting circles) and drive mechanisms starting at $400 and up are certainly available for Dobsonians.

Let me first say that I will NEVER let go of my ETX and its GoTo capability/portability, and have learned quite a bit about the night sky using it, but I've also learned that I have become somewhat dependent on its ability to find objects, and realize that I will never attain the level of knowledge the night sky has to offer in terms of knowing where objects are until I am FORCED to find them myself. This approach (thru star-hopping) may not be for everybody, but for those willing to take on the challenge, I believe it is one that, with time and patience, will provide a wealth of night sky knowledge.

Why be so concerned about knowing the night sky when you have that great GoTo scope to assist you in finding any object within reach of a given scope's aperture? The answer lies in those situations where something goes wrong (or could go much better) and the problem is associated with that GoTo feature, like improper alignment, battery/power failure, some form of mechanical/slewing problem, software glitch and/or something else that affects or disables that GoTo funtionality. It's at that time when, instead of calling it a night (especially when it seems like you've waited an eternity for good weather, right?), you can rely on your star-hopping techniques to get you through the observing session. Let's face it, if all else fails, you can at least use a binocular and/or your own two eyes to hunt down even relatively faint objects - or can you? Well, not unless you have a certain level of ability in knowing the night sky.

So, if you're like me, you might want to do yourself a favor when you can and practice a manual GoTo method, by using (1) a non-GoTo scope like a Dobsonian (if you have access to or can afford one), (2) the setting circles on the ETX, (3) a binocular, or (4) your own two eyes, all of these with a decent star chart. Perhaps you could practice one of these options when your ETX is working just fine, in order to LEARN THOSE CONSTELLATIONS; in fact, you don't even have to LEARN the constellations first - just learn how to star-hop, and learning the constellations becomes inherent in that task. I think you'll be glad you did WHEN you do have that GoTo "problem", and Murphy's Law says that in time, you will. Even if you were able to somehow escape Murphy's Law, you would still be satisfied by knowing the night sky a LOT better than you did before.

I'm hoping for the day when I can confidently say that I don't require the GoTo feature to find deep sky (or any other) objects. Again, I believe that with time and patience, that day won't be far off. Hats off to you folks with ETX's WITHOUT the Autostar, and any other non-GoTo scope owner.

Finally, let me close by saying that for those who choose to rely strictly on the GoTo feature to find objects, that's perfectly fine, because that's what a lot of this hobby is all about - personal choice. However, I also want to personally experience the work it takes and the satisfaction gained by finding objects without that magnificent GoTo feature - and learn the constellations much better by star-hopping. To me, having a GoTo scope AND mastering the star-hopping technique is kind of like getting the best of both worlds. And, to many of us, the thrill of the hunt is just as important (and sometimes more important) than the find.


Land of the Midnight Twilight

By Tom Hagen

Think it takes forever to get dark around the time of summer solstice? Try going north six hundred miles and you'll still see twilight at midnight!

Everybody has heard of the "Land of the Midnight Sun" which lies north and south of the Arctic and Antarctic Circles respectively, but have you heard of midnight twilight which is an effect seen in latitudes higher than about 48.6 north or south? Note that the border of the US and Canada west of Lake Superior is 49 N, or is about the latitude above which midnight twilight may be observed.

On Kathy's and my recent vacation to Moose Factory in northern Ontario, latitude 51.2 north, during the week of summer solstice, I witnessed twilight in the north at midnight. The moon was new that week, so it was quite obvious that there was still twilight due north at midnight, or about 1 AM EDT. After local midnight, it was apparent that it was getting lighter again in the northeast as dawn approached.

The definition of midnight twilight, as found in the 2001 Royal Astronomy Society of Canada Observer's Handbook, is the time astronomical twilight ends, or when the center of the sun has dipped to 18 below the horizon. Thus for latitudes of greater than 48.6 N and S, including atmospheric refraction, at times, twilight never ends, occurring only on the night of the solstice at exactly at 48.6 N and S, and lengthening in duration in the days both before and after the solstice as latitude increases. (Atmospheric refraction raises the Sun about 34' above the true Sun, or about one solar diameter.)

Of course, starting at the Arctic and Antarctic Circles, this effect results in the Sun itself being visible at midnight. Again because of atmospheric refraction, the midnight sun is first seen at 65 44', whereas the Arctic/Antarctic Circles are actually at 66 34' latitude North and South. Midnight sun is defined to occur when the top limb of the Sun is just visible above the north horizon.

On an observational note, the skies up there are exquisitely dark. Even with twilight at midnight, the structure of the Milky Way was clearly visible, I could see the rift in Cygnus, the bulge in Sagittarius, and the Scutum star cloud, and so on. In Sagittarius, the Lagoon Nebula and one or two of the other M-objects were visible. The North American Nebula was easily seen in my 11x70 binos, and I easily spotted another dozen or so M-objects around the sky.

At that latitude, Scorpius's tail dips below the horizon, and the Teapot of Sagittarius is riding really low near the horizon. Mars, though glowing as bright as ever is quite low in the south too. In the north, Capella is circumpolar.

And since Moose Factory is on the Moose River tidal estuary, tidal changes in the water level of about 1.5-m difference occur every 6 hours. It was interesting to note that the tides seemed to lag the position of the moon by a few hours. In other words, high tide seemed to occur a few hours after the moon had passed the meridian, and low tide was correspondingly delayed. This may be an effect of the rather great distance the estuary is from the open seas. Moose Factory is at the extreme south end of Hudson Bay, and since the north end of Hudson Bay is about 1000 miles north, it could be that the tidal wave simply takes a few hours to pass from the Arctic Ocean to the south end of Hudson Bay. Your comments on my theory are welcome!

So, for a fun nature and astronomy vacation, take a trip to the GREAT NORTH!


Home | Club News | Event Calendar |Observation | Featured Article | Astronomy News | For Sale | Photo Gallery | Astronomy Links | Directions | About Us |Membership Form

All information 2001 Oakland Astronomy Club, Inc. unless otherwise noted.

Web page last updated: November 16, 2006