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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Making free, custom charts for your night sky

Exactly what you see in the night sky depends upon where you are on Earth. The charts used on this  Prime Time web site are primarily for those living in mid-northern latitudes. But you can easily create free charts for your observing location. What’s more, you can customize these charts  so they meet the Prime Time goals of learning the bright stars and selected asterisms as they rise in the east. This post will show you how.

We all live on a ball and we look out at the “dome” of the sky as if we were living inside a globe. This means that exactly what we see and when we see it depends on where we live. If you live near mid-northern latitudes – that is, if you live in the highlighted area shown in the map below – the star charts and information  on the Prime Time web site should be very helpful to you because your night sky will look much the same as mine.

This map shows that by centering on 40 degree north latitude as a viewing location  our charts will work reasonably well for a large portion of the world's population that lives in the northern hemisphere. Outside that rgeion you need to make significant adjustments - and the southern hemisphere is another story entirely. Sorry ;-(

This map shows that by centering on 40 degree north latitude as a viewing location our charts will work reasonably well for a large portion of the world’s population that lives in the northern hemisphere. Outside that region you need to make significant adjustments that, fortunately, are easy with the free chart maker described here.

But if you live in other sections of the northern hemisphere – or even in the southern hemisphere, I urge you to follow the instructions below to create your own charts. In fact, you may find it interesting to try this free online chart source no matter where you live because then you can generate your own charts for your specific needs of the moment. Even if you live in the southern hemisphere, this chart-making Web site will be of use to you, though many of my specific examples on Prime Time will be of limited use. This is because  southern hemisphere dwellers, while seeing  many of the same stars and constellations that those of us in the northern hemisphere see, will see these stars at different times, and in different parts of  the sky than mentioned on Prime Time – and, the bright asterisms I give as guides may be hard to recognize since their orientation can be entirely different when seen from the southern hemisphere. Still, the basic principle of learning the brightest stars as they come out 45 minutes after sunset, rising in the east, holds.  The charts you make will help you do this.

Exactly how your view of the sky changes is complex and depends on not only where you are looking from, but what area of the sky you’re looking at.  When looking due south or north, the changes are most dramatic – looking due east, as we urge you to do when learning the sky, the changes are less dramatic, but still can be confusing. What follows are charts created with the Your Sky online chart maker. All are for 45 minutes after sunset (local time) on August 1, 2009, and all are the view when looking due east. The Prime Time goal in this instance is to learn the three bright stars of the “Summer Triangle”  – Vega, Deneb, and Altair. But notice how the position of these stars in the sky changes  – and the orientation of the triangle they form changes as well, depending on your viewing location.

Here's what I see in my eastern sky from near Boston, MA and this is the default view for charts on this web site.

Here's what I see in my eastern sky from near Boston, MA, and this is the default view for charts on this Web site.

Viewing from Anchorage, Alaska looks very similar to view from Boston, but notice how the orientation has changed. The other big change for Anchorage is on August 1 you will be in perpetual twilight - your night never gets fully dark at that time of year. That's good for learning bright stars, but hard when you wnat to look at faint objects.

Viewing from Anchorage, Alaska, looks very similar to the view from Boston, but notice how the orientation has changed? The other big change for Anchorage is on August 1 you will be in perpetual twilight - your night never gets fully dark at that time of year. That's good for learning bright stars, but hard when you want to look at faint objects, such as the Milky Way.

ys_miami_st

In Miami. Florida, the sky appears to make a small shift to the north. That shift brings into view on this particular date the planet, Pluto - but you will NOT see this with your naked eye, or even with binoculars. It takes a fairly large telescope and plenty of patience to find Pluto. (The bright planets that do sometimes appear in the east shortly after sunset are Mars, Jupiter, and Saturn.)

And now the view from “down under” – the southern hemisphere!

In Sydney, Australia th eview canbe quite different. You will see the same bright stars and the "Summer Triangle," but not for an hour or two later. Notice that one star - Altair - is just putting in an appearance on the horizon. The other will rise in the northeast for viewers in Sydney, but quite a while after sunset. Meanwhile, on this same date viewers in Sydnet are seeing the moon in their eastern sky - and if they have a telescope and lots of patience, Pluto.

In Sydney, Australia, the view is quite different. You will see the same bright stars and the "Summer Triangle," but not for an hour or two later. Notice that one star - Altair - is just putting in an appearance on the horizon. The others in the triangle will rise in the northeast for viewers in Sydney, but quite a while after sunset. Antares is also a guidepost star that we introduce in June, but is not visible in the eastern sky of our northern locations. Meanwhile, on this same date viewers in Sydney are seeing the moon in their eastern sky - and if they have a telescope and lots of patience, Pluto.

The Web site that generates these custom charts is called Your Sky, and while it includes excellent directions, the directions that follow are aimed at helping you generate custom charts that complement the Prime Time approach to learning the night sky – charts such as we include here, but that match your location. Making your first chart may take 10 minutes – but when you return to make others you’ll find it quick and easy.

Remember there are three critical elements to the Prime Time learning method:

  • focus on only the brightest stars and easily recognizable asterisms
  • observe objects as they appear to rise in the east
  • begin each observing session 45 minutes after sunset so you learn to find these bright stars and asterisms as they come out and before the sky is cluttered with many fainter stars.

So when you customize the charts on the Your Sky Web site using the instruction which follow, the goal is to optimize the chart for this use.

Preliminaries

You will need to know your latitude and longitude rounded to the nearest degree. If you don’t, go here (opens in new window/tab). Be sure to note whether your latitude is “north” or “south” and whether your longitude is “east” or “west.”

Remember to start your observing session 45 minutes after local sunset. To find the time of local sunset anywhere in the world for any date go here.

You will need to know the time and date you plan to observe in Universal Time – which used to be called Greenwich Mean Time. Most web sites and books give directions for changing Universal Time to your local time. Thus the conversion factor for Eastern Daylight Savings Time is usually given as  -4 – which means you subtract 4 hours from Universal Time to get EDST. For creating  star charts at Your Skies, you need to go in the opposite direction. To get the conversion factor for your time zone go to this web site.  (Universal Time is commonly used for astronomical events so that anyone, anywhere in the world, can thus calculate the local time for an event. You will find frequent use for it when you observe the night sky.)

Finally, planets on the Your Sky charts are identified by their common symbols show, in this graphic from NASA.

planet_symbolsI highlighted the three planet symbols most important to us – Mars, Jupiter, and Saturn – because these are the three bright planets that sometimes appear in our eastern sky after sunset and so may get confused with a bright guidepost star.

Step-by-step chart making

  1. Go to the Your Sky Web site. (Link opens in a new window/tab.)
  2. Scroll down to the “Horizon View” section and click “Make Horizon View” button.  At this point the settings do not matter.  Just press the button and don’t panic when you see the rather cluttered chart – you are going to modify your settings significantly in the form below the chart, then update it.
  3. Scroll to the form below the chart. You want to make it look much like the form to the right – but with your location and time. (Click the image of this form for a much larger view in a new window or tab.)
  4. You should uncheck most of the choices on the form to customize this chart. Here are the choices you want to make and what to put in each box. (The form at right is filled out in this way, but you need to substitute your specific information.)

    Click image of form to get a larger view in a new window or tab - you can then switch back and forth between windows, or print this new image out to help guide your choices.

    Click image of form to get a larger view in a new window or tab - you can then switch back and forth between windows, or print this out to help guide your choices.

  • Choose Universal Time and put in the Universal Time for the date and place where you will be observing. Remember to start your observing session 45 minutes after local sunset. (See “preliminaries” above for Universal Time and time of local sunset)
  • Your Viewpoint will be in “azimuth” and  set to 90 degrees. That means you’re looking due east.
  • Set the Field of view for 90 degrees. This will cover your horizon from northeast to southeast. (If this doesn’t capture what you want, you can increase the viewpoint to 180 degrees, but this tends to distort. You may want to change the azimuth instead – “0” would be north; “180” would be south. And notice the “pan” buttons just below your chart that allow you to move your view to the right or left.)
  • Set the latitude and longitude for your Observing Site.  (See preliminaries.)
  • Leave most of the “Display Optionsunchecked. You want a simple map.
  • Moon and planets”  should be checked because if there are any bright planets in the east they will look like stars and confuse you if not identified.  Planets are “wanderers” and one month may be there, and the next not. There are just three  bright planets  that might appear in the eastern sky in the early evening –  Mars, Jupiter, and Saturn.  (Mercury and Venus are seen only in the western sky in the early evening, or the eastern sky in the early morning.)
  • The important settings are for the stars. Set “Show stars brighter than magnitude” to 3.5 – and check “Names for magnitude” and set it for 1.5 and brighter.  The first setting means that all the stars of the bright asterisms we use will be included, but none of the dimmer stars which aren’t visible until the sky is fully dark and generally add confusion. By naming stars brighter than magnitude 1.5 you will have names for all the guidepost stars we use with the exception of Polaris, the North Star – to have that named you would need to set this to 2.5 and be looking north (0) not east (90). (To learn about the magnitude system go here.)
  • Color scheme” is a matter of personal preference. I prefer  “white on black background” for computer display. For printing you’ll use a lot less ink if you choose “black on white background.”
  • “Image size” I usually leave at 512 pixels. This really depends on your screen size. Try it. If too small and you have plenty of unused screen real estate, you can easily increase it.

That’s it. Just push the “update” button (between chart and form) and you will have a chart showing the bright stars – the ones that will put in an appearance about 45 minutes to an hour after sunset –  in the eastern sky for where you’re observing.

The Big Dipper is a familiar asterism within the constellation Ursa Major outlined here in a "Your Sky" chart.

The Big Dipper is a familiar asterism within the constellation Ursa Major outlined here in a "Your Sky" chart.

Can you do more with this? Yes – of course. For example, if you are looking for a bright asterism, check “Constellations: Outlines.” Most of the bright asterisms we use are part of a constellation and you can probably spot the asterism within the constellation outline. For example, the Big Dipper is a bright asterism that is part of the Constellation Ursa Major.

You can easily change the direction you are looking and brightness of stars visible.  My first concern is to give you a way to generate charts similar to the ones I use in the Prime Time Web site, but adjusted for your location.  Here are a few more suggestions. If you are in a heavily light-polluted area and you want to observe after it gets fully dark, you may still  want to restrict the brightness of stars to 4 to roughly match what you see.  In a rural area this can be set to 6 – the generally accepted limit for naked eye observing roughly 90 minutes after sunset when it is fully dark.

If you want a more elaborate star chart with many more details, I suggest you get one of the planetarium software programs and learn to use it. I use “Starry Nights Pro.” but this comes in several variations at different prices and for observing with naked eye and binoculars the simpler and less expensive versions are fine.

Many amateur observers I know prefer “The Sky” software.

And there is a new, free, planetarium program I’ve used a little called “Stellarium.” I really like its graphics, but I’m more comfortable with Starry Nights, a program I have used for years.

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