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View Full Version : 1950 vs 2000 epoch - something the amateur needs to be aware of?



Tucson_Tim
2007-Jun-11, 02:35 AM
I have a 1950 epoch Norton's Star Atlas and I also have the 2000 epoch version. Are the differences enough for an advanced amateur astronomer to be concerned? I don't consider myself an advanced observer and I "star-hop" to find items so it hasn't impaired me any...

Hornblower
2007-Jun-12, 12:45 AM
For star-hopping to an object that is on the chart as published, it is immaterial.

If you need to mark the position of an uncharted object, make sure the published position of the target is the same epoch as the chart.

I sometimes find a faint object by using the setting circles to do a declination and right ascension offset from a nearby bright star, using the published coordinates for both objects. This is when moonlight or city light pollution precludes star-hopping. Of course, make sure the positions for both objects are in the same epoch. If they are only a few degrees apart, the ill effects of even 50 years of precession are negligible compared with the uncertainty of aligning the equatorial mount and reading the setting circles. For this purpose the precession moves both objects by virtually the same amount in both coordinates.

If you use an accurately calibrated go-to mount, any object in its database is good to go. If you are punching in the published coordinates of something not in the database, make sure that position is in the same epoch as whatever was used for calibration.

If the only available information is in the wrong epoch, Norton's has precession tables which can be used to correct it.

Tucson_Tim
2007-Jun-12, 02:23 AM
If you use an accurately calibrated go-to mount, any object in its database is good to go. If you are punching in the published coordinates of something not in the database, make sure that position is in the same epoch as whatever was used for calibration.

If the only available information is in the wrong epoch, Norton's has precession tables which can be used to correct it.

Thanks for the response. One of these years I may get a go-to mount but for now it's the old equatorial mount with clock drive and setting circles.

Dave Mitsky
2007-Jun-12, 05:55 AM
I have a 1950 epoch Norton's Star Atlas and I also have the 2000 epoch version. Are the differences enough for an advanced amateur astronomer to be concerned? I don't consider myself an advanced observer and I "star-hop" to find items so it hasn't impaired me any...

Tim,

I would think that any advanced amateur astronomer observing today would be using the Uranometria 2000.0, the Millennium Star Atlas, and/or planetarium programs like The Sky, Starry Night Pro, SkyMap, and Megastar.

At any rate, the differences in coordinates are rather small and don't really affect star-hopping as has already been stated. See http://www.arksky.org/cgi-bin/epoch2.pl for an 1950 Epoch to 2000 Epoch converter.

Dave Mitsky

Tucson_Tim
2007-Jun-12, 02:40 PM
Tim,

I would think that any advanced amateur astronomer observing today would be using the Uranometria 2000.0, the Millennium Star Atlas, and/or planetarium programs like The Sky, Starry Night Pro, SkyMap, and Megastar.

At any rate, the differences in coordinates are rather small and don't really affect star-hopping as has already been stated. See http://www.arksky.org/cgi-bin/epoch2.pl for an 1950 Epoch to 2000 Epoch converter.

Dave Mitsky

Thanks Dave!

BTW, is there any way you could post the next month's sky events (July)? You currently post this month's events in its own locked thread.

In particular, I was wondering if Venus will catch up to Saturn or will its "fall" towards the Sun (towards inferior conjunction) keep that from happening?

Tim

Tucson_Tim
2007-Jun-12, 02:53 PM
Dave,

This is from your June events thread:



Venus and Saturn grow closer together during the course of the month, the distance between them shrinking from 23 degrees on June 1 to 0.7 degree on June 30.


Is this the conjunction on Jun 30th?

Dave Mitsky
2007-Jun-14, 01:54 PM
Thanks Dave!

BTW, is there any way you could post the next month's sky events (July)? You currently post this month's events in its own locked thread.

In particular, I was wondering if Venus will catch up to Saturn or will its "fall" towards the Sun (towards inferior conjunction) keep that from happening?

Tim

There certainly is a way that I can post the July calendar, i.e., when it has been completed, in about a week or so. It takes me at least 10 hours to compile, correct, e-mail, and post my monthly celestial calendar and each and every month I find myself wondering why I bother to do it at least once.

What do you mean by catch up? The two planets are in conjunction on June 30. A week before the conjunction Venus will be positioned to the lower right of Saturn. Saturn then begins to "fall" away from Venus and will be about 4 degrees to the right of Venus a week afterwards.

Dave Mitsky

Dave Mitsky
2007-Jun-14, 02:03 PM
Dave,

This is from your June events thread:



Is this the conjunction on Jun 30th?

Yes.