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Reading a star atlas

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#1 ADSmithTN

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Posted 28 February 2021 - 11:20 AM

So I bought Will Tirion's Cambridge Star Atlas off eBay. I found out after the fact it's a second edition so I hope that doesn't hurt me too bad. Anyhow are there any resources to help with understanding the star atlas? Maybe I'm just dense, I get the constellation charts but I'm having a hard time making sense of the chart section. I just can't tell what I'm looking at.
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#2 davejlec

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Posted 28 February 2021 - 01:25 PM

Welcome, Newbie!  Matching the charts to the sky is a matter of scale. Tonight, Orion crosses the meridian about  7 o'clock Eastern time. It is on chart 9 of the atlas, along with the Hyades Cluster to the NW and the Pleiades cluster (M45) further NW.  The scaling of the charts are a bit small -  the actual main stars in Orion appear more spread out than the charts show, even if held up close.  Of course, if one is looking due East, then the charts should be rotated accordingly ( with the left side of the chart facing down). If  facing West, left side of charts should face up. Know how to locate Polaris and the meridian becomes more obvious. All celestial objects arc to their highest altitude when crossing the meridian.  Locate the "Winter Triangle" of Sirius, Procyon and Betelgeuse (also on chart 9) and notice the arc Procyon makes in comparison to the arc of Sirius.      


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#3 ADSmithTN

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Posted 28 February 2021 - 01:52 PM

Welcome, Newbie! Matching the charts to the sky is a matter of scale. Tonight, Orion crosses the meridian about 7 o'clock Eastern time. It is on chart 9 of the atlas, along with the Hyades Cluster to the NW and the Pleiades cluster (M45) further NW. The scaling of the charts are a bit small - the actual main stars in Orion appear more spread out than the charts show, even if held up close. Of course, if one is looking due East, then the charts should be rotated accordingly ( with the left side of the chart facing down). If facing West, left side of charts should face up. Know how to locate Polaris and the meridian becomes more obvious. All celestial objects arc to their highest altitude when crossing the meridian. Locate the "Winter Triangle" of Sirius, Procyon and Betelgeuse (also on chart 9) and notice the arc Procyon makes in comparison to the arc of Sirius.


This actually does help more because when looking at chart 9 I actually recognize what I'm looking at in relation to the night sky. I had been looking at chart 4 for Ursa Major and just couldn't make out the constellation. The scale example did it though, I was looking for something bigger, I see it now, many thanks! So what importance are the RA and DEC if you know what you're looking at?

#4 Dave Mitsky

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Posted 28 February 2021 - 02:05 PM

Orion culminates or reaches its highest elevation at approximately 7:00 p.m. local time.  (Culmination occurs when a celestial object transits the meridian.)  Chart 9 gives a good representation of how the constellation will look at that time with the exception of scale.

If you can find a copy of the out-of-print Bright Star Atlas 2000.0 at a reasonable price, the charts within may be more useful, since they show a larger swath of the sky but at a smaller scale, of course.  A planisphere may be helpful, as well.

I've included a screen capture from Stellarium showing the southern sky at 7:00 p.m. from a latitude of 40 degrees north.

Attached Thumbnails

  • Orion Stellarium 2-28-21.JPG

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#5 Dave Mitsky

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Posted 28 February 2021 - 02:19 PM

So what importance are the RA and DEC if you know what you're looking at?

If you have an equatorial mount with good mechanical setting circles, you can locate objects using their celestial coordinates.  Entering those coordinates into the computer in a go-to mount will move the telescope to that location.

https://www.skyatnig...etting-circles/

 

Learning RA and Dec. provides you with a golden key to unlock the position of any object in the night sky. Before computer software effortlessly plotted the paths of newly discovered comets and fast-moving asteroids, I couldn't wait to get my hands on their coordinates. I'd hand-plot the positions on a paper star atlas, then swing my scope to the spot, and thrill when I found it on my own.
 

RA and Dec. also come in super-handy if you have a Go To telescope and a new comet or nova is discovered. Just input its coordinates, hit enter, and you're there. If you hear of a new comet or fast-moving asteroid, a quick check of its changing coordinates will tell you not only where it is but where it's headed, so you can plan the best time to see it.

https://skyandtelesc...al-coordinates/

 

https://skyandtelesc...al-coordinates/

http://www.pas.roche...oordinates.html


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#6 kksmith

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Posted 28 February 2021 - 04:23 PM

Star charts are nothing more than topo maps of the night sky. If you know how to use a topo map and can read/plot grid coordinates, then you can easily use a star chart. RA and Dec are the grid coordinates of the items on that stellar topo map. Once you orient the chart to the lay of the land aka your view of the night sky - you can navigate unknown terrain. You can use RA/DEC in go to system just like plugging grid coordinates into a GPS device. Or if you're Old School and like map and compass, you can dial it in on a GEM. Or like me - I use line of sight - pick a point and off I go. Of course being mindful of my back azimuth.

 

But if you're 2Lt - you're gonna get lost any way, so bring some slap flares so we can come get you. 


Edited by kksmith, 28 February 2021 - 04:25 PM.

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#7 Sheol

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Posted 28 February 2021 - 07:26 PM

                                    You have to learn to tilt the maps to match what the stars look like to you, after removing the lines. I actually find the lines somewhat annoying as different people tend to draw some small details differently & under a dark sky, that can be a bit confusing. Certain constellations do not have set patterns.

 

                           Clear Skies,

                                  Matt.


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#8 JOEinCO

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Posted 01 March 2021 - 04:40 AM

So I bought Will Tirion's Cambridge Star Atlas off eBay. I found out after the fact it's a second edition so I hope that doesn't hurt me too bad....

Great advice from others so far. But I wanted to point out the Second Edition will be just fine. You will eventually want something with better scale (i.e. more charts to cover the whole sky), but any edition of the Cambridge will serve you well. Consider the S&T Pocket Atlas Jumbo Edition for your next atlas, when the time comes, but keep that Cambridge even then.


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#9 radiofm74

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Posted 01 March 2021 - 05:34 AM

Get good at matching your charts with the sky naked eye, because when you'll get your scope it will become more complicated: everything will be upside down and/or flipped side to side! grin.gif


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#10 geovermont

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Posted 01 March 2021 - 07:42 PM

It does take a while, but if you take it slow, you'll get it. A  planisphere or some other simplified sky maps helps too, although they have their own learning curves. They help you learn the constelations and to develop a sense of how the heavens appear to rotate over you as the night progresses and as the seasons pass. The atlas is best for zooming in on the details. But you're right, first you have to get oriented on that atlas page.  I find the Sky and Telescope Pocket Sky Atlas (Jumbo Edition) the very best for me, but work with what you have for now. After a few evenings of use it will all make more sense.




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