Getting Started

On the main sky-chart page you'll find links to launch the "Interactive Sky Chart." You'll also see a link to Sky Chart Help, which you should read if you get stuck or want more detailed instructions.

Click one of the "Interactive Sky Chart" links. This will launch the sky-chart applet (which will take a minute or two to load if you have a slow Internet connection) and open a Choose Location dialog box. Enter "Denver" in the City box, choose "Colorado" from the State/Province list, and select "USA" from the Country list. Then click the Submit button. Next you'll see a Choose Time Zone dialog box; note that Denver is reported to lie almost exactly at 40° north, the latitude of Sky & Telescope's northern evening sky chart. Pick "Mountain Time" from the list, check the Daylight Saving Time (DST) box, and click Submit again. Now you'll see a sky chart for this evening (whatever the date) at 9 p.m. local daylight time in Denver.

On the right side of the screen is 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.

The All-Sky Chart's center represents the sky directly overhead. Its circular rim represents the horizon; compass directions are labeled around it. A star that's plotted on the map halfway from the edge to the center will be found halfway up the sky — that is, 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; it measures 50° wide by 40° tall. Compass directions are abbreviated along the bottom, and two markers partway up the right edge indicate your viewing altitude, from 0° at the horizon to 90° overhead.

Let's change the date to October 16, 2002, and the time to 8:30 p.m. to match the circumstances of the northern evening sky chart in our October 2002 issue. In the Date & Time display at the lower left of your screen, click once on the name of the month; it will become highlighted. Now click the + or – buttons to change the month to October. Next, highlight the date and use the + or – buttons to change it to 16. Make sure the year reads 2002. Then do the same thing for the time, highlighting first the hours, then the minutes, and using the + or – buttons to set it to 8:30 p.m.

Now compare the All-Sky Chart in your Web browser to the one in the magazine: they match, right down to the position and phase of the Moon for midmonth! (Although the Moon's phase is indicated properly, the orientation of the terminator — the line between the illuminated and shadowed parts of the disk — is not; it is always shown as vertical.) If you wish, you can choose which objects and labels get displayed on the chart by clicking on the Show Advanced Display Options link under the Date & Time area and making your selections.

Now would be a good time to play with the applet to see how it behaves. Click anywhere inside the green box on the All-Sky Chart, then drag the box around the sky and watch what happens in the Selected View. Or do the opposite: click within the Selected View and move the cursor around while you watch what happens on the All-Sky Chart. Be as adventurous as you'd like. If you run into trouble, click the Help button at upper right or close the applet, return to the main sky-chart page, and start over.