Sky Chart Help

Interactive Sky Chart
When you launch Sky & Telescope's Interactive Sky Chart applet, you'll get a naked-eye view of the sky on the left and an all-sky chart on the right, for any location and date you choose.

Sky & Telescope's Interactive Sky Chart is a Java applet that simulates a naked-eye view of the sky from any location on Earth, at any time of night, on any date between 1600 and 2400 A.D. Charted stars and planets are the ones typically visible without optical aid under clear suburban skies. Some deep-sky objects that can be seen in binoculars are plotted too.

The applet should work properly in most Java-enabled Web browsers. For best results on a PC, use Internet Explorer 6 or Netscape 7; on a Mac, use OS X 10.3 with Safari. If you have trouble getting the Sky Chart to open on your computer, please review our detailed system requirements to check whether you're using a supported operating system and/or to download one of the supported browsers.

There are three common reasons for trouble with the Interactive Sky Chart:

1. Security Warnings If your Java is up-to-date but you receive security warnings when you attempt to access the Interactive Sky Chart, it's because we have always self-signed the Java security certificate, but as of the most recent Java update, this is no longer allowed. There is a workaround that will not harm the security of your computer, instructions are listed below

2. Black Screen If the Interactive Sky Chart shows you a black screen, check to see if you need a Java update: go to Java.com and click on "Do I have Java" to verify your Java version. Downloading a new or updated version of Java is free. Depending on your browser, you might need to activate the Java plug-in after updating.

3. Change Location Doesn't Work if the "Change Location" button isn't working, check to make sure you don't have a "pop-up blocker" installed, which will block new browser windows from opening automatically. The "Change Location" button opens a new browser window.

4. Slow Connection You might have a problem with your Internet connection. This is especially likely if you are seeing pages on other Web sites load very slowly. We suggest you contact your Internet service provider in this case.

Quick links:


How to Work Around Java-Related Security Warnings

If you see a Java-related security warning when you attempt to open the Interactive Sky Chart, you'll need to follow the steps below to enable the Sky Chart for your computer. We are working to update the Interactive Sky Chart so that it does not produce these types of errors, but this workaround will help you access the Sky Chart in the meantime without harming the security of your computer.

In Windows computers:

1. Click the "Start" button and select "Control Panel".
2. Select "Java" - if you are showing large or small icons, you shouldsee
"Java" listed there. If you are using the "Category" layout, select
"Programs" then "Java"
3. When the Java Control Panel opens, select the tab marked "Security"
(see screen shot below)
4. Click "Edit Site List..."
5. Click "Add"
6. In the little box marked "Location", type in the skychart's address:

http://skychart.skyandtelescope.com/skychart.php

7. Click "OK". You may get another warning message about http locations
being a security risk, but click "Continue"
8. Click "OK" to close the Java Control Panel

In Macs:

1. Click the apple icon in the uppser left corner, then choose "System
Preferences..."
2. Select "Java"
3. Follow steps 3 through 8 above.


How to Open the Sky Chart

Go to the Interactive Sky Chart by clicking on the link from the website header, then click on the Interactive Sky Chart link within the article. The applet may take time to download, especially if you have a slow connection.

If you haven't previously set your default observing location, the chart will open with the location set to Greenwich, England. Set the location by clicking on the "Change Location" button. (Pop-ups need to be enabled for our site for this button to work.) Enter your observing location in only one of the three sections available for this purpose: USA or Canada, World by City, or Worldwide by Latitude & Longitude. Then click the corresponding SUBMIT button. (If you run into trouble at this stage, see the more detailed instructions in How to Change Your Location and Time Zone.) Once you've set the location, it'll be remembered in a cookie on your computer.

The time zone is set automatically from your location, and the default time is 9:00 p.m. You can change the time by clicking the arrows next to the hour shown or you can set both date and time by clicking on "Change" in the Date & Time section. If daylight saving time is currently active in your area, check the small box to the right of the words Daylight Saving Time. Then click the SUBMIT button.

The Interactive Sky Chart should now appear on your screen, showing the sky visible tonight from your location at your specified local time:

Sky Chart Combined View
The main screen of Sky & Telescope's Interactive Sky Chart is called the Combined View. It features the All-Sky Chart at right and Selected View at upper left.

On the right side of the screen you'll see a circular map of the constellations labeled ALL-SKY CHART, with a green, four-sided frame near the edge labeled WEST. The part of the sky inside this frame appears at a larger scale in the rectangular window labeled SELECTED VIEW in the upper left corner of your screen. Under that you'll find Location and Date & Time displays. This page is known as the Combined View.

The All-Sky Chart's center represents the part of the sky directly overhead. Its circular edge represents the horizon all around you, as if you were standing in an open field and turning around in a complete circle. Compass directions are labeled around the horizon/edge.

A star that's plotted on the map halfway from the edge to the center, therefore, can be found about halfway up the sky — halfway from horizontal to straight up.

The Selected View shows about as much sky as you can take in at once with your unaided eyes; the field of view is about 50 degrees wide by 40 degrees tall. Compass directions are abbreviated along the bottom, and two markers partway up the right edge of the window indicate your viewing altitude, from 0 degrees at the horizon to 90 degrees overhead.

If you cannot see the bottom or part of the side of the sky chart, resize your desktop to 800 x 600 pixels (or larger). To do this on a PC running Windows 95 or higher, go to the taskbar at the bottom of your screen and click Start > Settings > Control Panel > Display. On the Display Properties screen, click the Settings tab and move the Screen Area bar until it says "800 by 600 pixels." Then click OK. You'll get a pop-up window that says, "Windows will now resize your desktop;" click OK. Once your display is reset to the new size, another pop-up window will ask, "You resized your desktop, do you want to keep this setting?" Click OK again.


How to Change Your Location and Time Zone

From the Combined View (the dual-pane screen with the circular chart on the right and the rectangular window at upper left), click the CHANGE button in the Location display area toward the lower left of the screen. If nothing happens, check to make sure you aren't blocking pop-ups from our site, because the Change Location button opens a new browser window:

Choose Location Screen
Use the Choose Location screen to set the observing location used by the Interactive Sky Chart. Be sure to enter data in only one of the three sections.

All locations:

Be sure to enter data in just one of the three sections of this page: USA or Canada, World by City, or Worldwide by Latitude & Longitude. If you want to make the new location your default observing location, click the checkbox provided for that purpose. If you don't check the box, the new location will be used for this session only.

USA or Canada:

The simplest way to enter your location, and the approach recommended for first-time users, is to enter your Zip code (USA) or postal code (Canada) and choose USA or Canada from the country pull-down menu. When you click the SUBMIT button, the system will use this information to determine your city, state or province, latitude, and longitude.

If you enter your location by specifying a city, be sure to choose the corresponding entry from the state/province pull-down menu too, as well as the country (USA or Canada) from the country pull-down. Click the SUBMIT button. If the system can't find your city, or if you get a page listing several possible matches with the same city name but different geographic coordinates (latitudes and longitudes), go back and try entering a nearby city with a more unusual name. The Sky Chart's accuracy will not be compromised as long as the city or town you choose as your observing location is no more than 10 kilometers (6 miles) from your actual location.

Alternatively, if you have a good map or atlas handy, you could instead estimate your latitude and longitude and choose the best match to those coordinates from the list of multiple cities with the same name.

World by City:

Enter the name of your city or town, select your country from the pull-down menu, and click the SUBMIT button. If the system can't find your city in our database, try entering a common alternative spelling of the name, if any. If that doesn't work either, try entering the name of a larger city nearby.

If the information you enter causes the system to come up with several possible matches with identical city names but different latitudes and longitudes, follow the instructions in the USA or Canada section above.

Worldwide by Latitude & Longitude:

If you know your latitude and longitude or can find them using a high-resolution map or Global Positioning System (GPS) receiver, enter them in the spaces provided. All entries should be positive numbers. Degrees of latitude should fall between 0 and 90, minutes between 0 and 60; be sure to specify north (N) or south (S) using the radio buttons. Degrees of longitude should fall between 0 and 180, minutes between 0 and 60; be sure to specify east (E) or west (W). For reference, in North America latitudes are N and longitudes W, while in Australia latitudes are S and longitudes E. If in doubt, choose your location using one of the methods described above instead.

This option to set your latitude and longitude manually doesn't work very well. Instead, we recommend selecting a named location near you instead. Anything within 50 miles (80 km) will work fine. At the level of resolution of a full-sky chart, a 50-mile error in location is negligible.

An odd glitch is that when you do a Change Location, the Sky Chart with the corrected location pops up in a new window or tab, leaving the old one in place. That's OK — just close the old window and proceed with the new one.

Once you have successfully entered your location, you'll see the Choose Time Zone screen:

Choose Time Zone Screen
Use the Choose Time Zone screen to set the time zone appropriate to your observing location.

Note that you cannot get to the Choose Time Zone screen directly from the Combined View, All-Sky Chart, or Selected View — you must go through the Choose Location screen first.

First verify that the location displayed there is correct. If it isn't, click on the Change Location link to return to the Choose Location page. Otherwise, select the time zone appropriate to your location from the pull-down menu. The system will not check whether your time-zone selection matches your location. If you're unsure of the time zone for the location you've selected, you may be able to figure it out using SwissInfo.net's Local Times Around the World page. Don't forget to check the Daylight Saving Time box if appropriate. Then click the SUBMIT button; you'll be returned the Combined View, where you'll see a depiction of the sky for the location you've selected.


How to Change the Date and Time

There are two ways to change the date and time for which the Sky Chart shows the sky. First, from the Combined View (the dual-pane screen with the circular chart on the right and the rectangular window at upper left), click the CHANGE button in the Date & Time display area at the lower left of the screen. This will take you to the Choose Date & Time page:

Choose Date and Time Screen
Use the this screen to set the date and time for which the Sky Chart shows you the visible sky. This is also where you tell the applet whether to use daylight saving time.

Choose any date between 1 January 1600 and 31 December 2400 using the day and month pull-down lists and the year text-entry box. If daylight saving time was, is, or will be active for your current observing location on your selected date, check the small box to the right of the words Daylight Saving Time. If you wish to change your location and time zone, use the link supplied.

If you want the Sky Chart to use Universal Time (UT) rather than local time, check the small box provided for that purpose. UT, which is essentially the same as Greenwich Mean Time, is used worldwide by astronomers and others to avoid confusion between time zones.

Date and Time Controls
With the date and time controls in the Combined View, you can step backward or forward in time — just highlight the field you want and click the + or – button.

The second way to change the Sky Chart's date and time is to click on the month, day, year, hour, or minute in the display at lower left in the Combined View (under the Date & Time heading), which will become highlighted (in the following example, the hour field has been selected):

Then use the + or – button to increase or decrease the value you've selected. Each time you change a quantity, both the Selected View and All-Sky Chart will be updated instantly.


How to Change the Sky Chart's Display

Change the Field of View:

Besides changing the observing location and date/time for which the Sky Chart shows you the constellations, you can change which part of the sky is featured in the Selected View. Click on the area of the All-Sky Chart that you'd like to see in more detail. The green frame will jump to where your cursor is pointing, and the scene in the Selected View window will now show this area.

Or, click and hold down your mouse button within the green frame on the All-Sky Chart, then drag the frame around the sky. The scene in the Selected View window will change as the location of the green rectangle on the All-Sky Chart changes.

Or, click and hold down your mouse button in the rectangular Selected View window, then drag the cursor to move to another part of the sky. The green frame in the All-Sky Chart will follow your movements.

Maximize the View:

The Combined View packs a lot of information into a small amount of real estate on your computer's screen. If you click the MAXIMIZE button under the All-Sky Chart or Selected View, that field will enlarge to fill the applet's 800-by-600-pixel window. In reality, the All-Sky Chart doesn't get much bigger, because even in the Combined View it already spans almost the entire height of the window. But the Selected View enlarges severalfold. The field of view remains the same as before, but the display is much larger and more readable. Note that when the Selected View is maximized, you can still move around the sky by holding down your mouse button and dragging the cursor.

To return to the Combined View, click on the BACK TO COMBINED VIEW button in the lower right corner of the maximized view.

Customize the Display:

Click on the SHOW ADVANCED DISPLAY OPTIONS button located in the bottom left corner of the Combined View (the dual-pane screen with the circular All-Sky Chart on the right and the rectangular Selected View window at upper left). This will take you to the Advanced Display Options screen:

Advanced Display Options Screen
Use the Advanced Display Options screen to control which features of the Selected View and All-Sky Chart are turned on or off.

Click the various checkboxes on or off, depending on what you'd like to see in the All-Sky Chart and Selected View, which can be controlled independently. The Interactive Sky Chart displays the following:

  • The 1,686 brightest stars down to magnitude 5.0; of course, only half of these are above your horizon at any one time. You can toggle labels on or off for 26 named stars.
  • The Sun, Moon, and five naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn); you can toggle their labels (but not their symbols) on or off. Note that due to certain limitations of the software underlying the Sky Chart applet, the Moon's phase is indicated properly, but the orientation of the terminator — the line between the illuminated and shadowed parts of the Moon's face — is not; it is always depicted as vertical.
  • Selected deep-sky objects (star clusters, nebulae, and galaxies); you can toggle their symbols and labels on or off.
  • Selected special sky events such as meteor showers and bright comets, if any; you can toggle their symbols and labels on or off. Note that the Sky Chart displays special sky events for the current year and only a few years into the future.
  • Constellation lines and labels. In the Selected View, they're either on or off. On the All-Sky Chart, you can have no lines or labels, lines only, or lines and labels. In the latter case, a name shows up only when your cursor moves over a constellation; at the same time, the constellation lines become highlighted.
  • Buildings and trees are shown along the horizon in the Selected View. Sometimes they block celestial objects of interest that are low in the sky. If that happens, remove them by unchecking the appropriate box.

The RESTORE DEFAULT button resets any changes you've made to the chart's original settings. The CANCEL button returns you to the Combined View without changing any of the settings.


How to Print the Sky Chart

If you have a color printer and a generous budget for ink, you can print the maximized All-Sky Chart or Selected View in living color. Simply choose the view you want, then click your browser's PRINT button or choose File > Print from the menu bar. Use the landscape (wider than tall) setting for the Selected View; either the landscape or portrait (taller than wide) setting will work for the All-Sky Chart.

You'd probably rather not use so much ink all at once. So we've provided the capability to generate a black-on-white version of the All-Sky Chart as an Adobe PDF file suitable for economical printing on either a color or black-and-white printer. (Sorry, but this capability does not exist for the Selected View.)

In the lower-left corner of the All-Sky Chart, whether in the Combined View or maximized display, you'll see a CREATE PDF button. If you click it, your browser should call up a PDF file of the All-Sky Chart corresponding to the current date, time, and location settings. This may take a minute or two, and depending on which operating system and browser you're using, the PDF may open in the browser itself or in Adobe Reader.

The PDF chart will show all the objects, lines, and labels that the All-Sky Chart is capable of displaying, regardless of which boxes are currently checked in Advanced Display Options. As a result, the printable chart may look cluttered, and some labels (all of which are in the same orientation) may overlap others. Still, if you print this PDF, you'll have a chart reasonably well suited to use outside under the night sky. (You might be able to minimize label overlap by changing the chart's time by 15 or 20 minutes either way and generating a new PDF.)

Sky Chart PDF
A close-up sample of a printable PDF of our Sky Chart.

The foregoing assumes that you already have the free Adobe Reader program on your computer and that it is properly configured as a "helper" application for your web browser. If that's not the case, then rather than open the PDF automatically, your browser may ask you to save it to disk.

Note that the printable All-Sky Chart may not open if your copy of Adobe Reader is older than version 5.0 You can get a free upgrade to the latest version (7.0 as of May 2005) at Adobe's website. Adobe Reader is available for PCs and Macs running all popular operating systems.

Another alternative is to use one of the bimonthly sky charts provided in our Getting Started in Astronomy flyer, which is available in Adobe PDF format for observers in both the Northern and Southern Hemispheres. The maps in Getting Started produce high-quality 8½-by-11-inch (or A4) printouts in black and white. Here's a detail from one such printout:

Getting Started in Astronomy
A piece of one of the six bimonthly star charts in our Getting Started in Astronomy flyer.

These charts don't show the ever-changing positions of the Moon and planets. If you see a bright "star" near the line labeled "ECLIPTIC" that's not on the map, you've located a planet. To figure out which one it is, consult the latest issue of Sky & Telescope or use the Interactive Sky Chart).

If this Help page doesn't answer your questions, please send an e-mail message to help@SkyandTelescope.com. Describe your problem in as much detail as possible, and note which part of the site you were on when you got stuck. Thank you!