Frequently Asked Questions

Astronomy

1.1 What is that up to 6-digit HD number that appears when I click on a star?
1.2 What is the "vernal equinox" in the Solar System?
1.3 What is "mag: 1,25" in the detailed information of a star?
1.4 What is that up to 4-digit HR number that appears when I click on a star?
1.5 What is that up to 6-digit SAO number that appears when I click on a star?
1.6 What is the spectral type that appears when I click on a star?

How to use AstroViewer

2.1 How do I read the sky map? What exactly does it display?
2.2 Why are East and West reversed on the sky map?
2.3 I'd like to set my location, but I don't find my city in the list. What can I do?
2.4 How can I find out the names of the displayed constellations?
2.5 How many stars does AstroViewer's database of contain?
2.6 Does AstroViewer take into account daylight savings time?

Installation and operation of AstroViewer

3.1 I have downloaded and installed AstroViewer. Why can't I set the time?
3.2 I have bought the license key. Where do I have to enter it?
3.3 I have downloaded and installed the AstroViewer software again, but my license key seems not to work. What's wrong?
3.4 Can I use the AstroViewer shareware also under Mac-OS or Linux?
3.5 The button "Start AstroViewer" does not appear at the upper left. What can I do?
3.6 The AstroViewer Online applet gets blocked by the Java security settings. What can I do?

Astronomy

1.1 What is that 6-digit HD number that appears when I click on a star?

The HD number is the reference number of that star in the "Henry-Draper-Catalogue". This star catalog was published in 1918-24 and contains 225,300 stars up to a magnitude of 8 mag.

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1.2 What is the "vernal equinox" in the Solar System?

The "vernal equinox" is a point in the constellation Fish where the celestial equator crosses the ecliptic and where the Sun is located on March 21 (the first day of spring in the northern hemisphere).

You can proof this definition in AstroViewer's solar system map when you set the date to March 21. At that date, the Sun is in the direction of the vernal equinox, seen from the Earth. Then switch to the sky map and activate the celestial equator and the ecliptic. You will find the Sun at the point where both lines cross each other in the constellation Fish.

The vernal equinox is generally accepted reference point for astronomical coordinates.

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1.3 What is "mag: 1,25" in the detailed information of a star?

"mag: 1.25" is the "magnitude" or apparent brightness of a celestial body. Stars with a smaller (even negative) magnitude are the brighter ones. Sirius is the brightest star with a magnitude of -1.46m. AstroViewer displays stars up to +5.0m, i.e. all stars visible with the naked eye.

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1.4 What is that up to 4-digit HR number that appears when I click on a star?

The HD number is the reference number of that star in the "Bright-Star-Catalogue". This star catalog lists all stars brighter than 6.5 mag.

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1.5 What is that up to 6-digit SAO number that appears when I click on a star?

The HD number is the reference number of that star in the "SAO-Catalog". This star catalog was published in 1966 and contains almost 229,000 stars up to a magnitude of 9 mag.

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1.6 What is the spectral type that appears when I click on a star?

The spectral type is a classification of the characteristics of the optical spectrum of stars. Roughly speaking, it tells you the color of the star.

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How to use AstroViewer

2.1 How do I read the sky map? What exactly does it display?

The sky map represents the entire visible celestial sphere. Zenith, i.e. the point directly overhead, is in the center of the map. The perimeter is the horizon.

The center of the display is the direction you are facing. You can change the viewing direction with the sliders "Rotation" (at the bottom) and "Inclination" (at the right). Moreover, you can use the zoom slider (at the left) to enlarge the viewing section.

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2.2 Why are East and West reversed on the sky map?

Compared to a street map, on which we look down, on the sky map East and West seem "reversed", because the sky map shows what we see looking up to the sky.

Imagine you are lying on the ground in a starry night and you are looking vertically up to the sky. Your feet are pointing to the south. West is at your right then and east at your left hand side, exactly like it is displayed on the sky map.

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2.3 I'd like to set my location, but I don't find my city in the list. What can I do?

To find your way in the night sky you don't need to set your location too precisely. Just choose the nearest city from the list or set your location on the world map (button "Location / City").

If you are missing a city in the city list, you can enter it yourself by clicking the button "Enter coordinates" in the dialog "Location / City". A new dialog pops up, where you can enter name and coordinates of the desired location.

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2.4 How can I find out the names of the displayed constellations?

Activate "constellation names" in the control field "Auxiliary lines". The names of the bigger constellations are displayed. While zooming in, the names of smaller constellations appear also.

Alternative way: Activate "constellation pointer" in the control field "Auxiliary lines". Name and outlines of the constellation you move the mouse pointer into will turn green.

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2.5 How many stars does AstroViewer's database of contain?

The star catalog of AstroViewer contains the 1,423 brightest fixed stars and Messier objects up to a magnitude of +5.0 mag. Sun, moon and the nine planets are shown as well.

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2.6 Does AstroViewer take into account daylight savings time?

If you have selected a location from the city list, daylight savings time is considered when displaying local time, if applicable.

If you have chosen a location from the world map, the local time may be derived from the longitude, applying no daylight savings time. In this case the time is marked with a * symbol.

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Installation and operation of AstroViewer

3.1 I have downloaded and installed AstroViewer. Why can't I set the time?

AstroViewer is shareware. In the first step you need to download and install the test version. The test version is restricted to the time range 1950 till 1959 (details...). Apart from that, all functions are available and can be tested.

To remove the time range limitation and so to enable the full time range a license key is needed. The license key turns the test version into the full version which features the full functionality. (How to obtain the license key...)

Anyway, you can use AstroViewer Online with almost the full functionality free of charge online.

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3.2 I have bought the license key. Where do I have to enter it?

When you have installed the AstroViewer test version and then start the program, an input dialog window for the license key will pop up.

The best way to enter the key is to copy it from the e-mail that brought it to you into the clipboard (mark it and press <Crtl>c) and then insert it in the input field by pressing <Ctrl>v.

Should the input field refuse to accept your input, click on the upper border of the input dialog window and enter the key again.

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3.3 I have downloaded and installed the AstroViewer software again, but my license key seems not to work. What's wrong?

If you have bought your license key before August 27, 2009, it is valid for the AstroViewer versions 2.10.x or 2.11.x. The current version is 3.1.6. For that version another license key is required, that can be obtained here.

The " old" AstroViewer versions 2.10.8 and 2.11.5 can still be downloaded (av2-10-8-setup.exe, av2-11-5-setup.exe). Your "old" license key will do with one of these versions.

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3.4 Can I use the AstroViewer shareware also under Mac-OS or Linux?

Yes, you can, ...

... but unfortunately, I haven't tested it. On the other hand, there are many users who have, and they have told me that it works. So, if you would like to run the AstroViewer shareware under Mac-OS or Linux, download the jar file "av3-1-6.jar". Save it to a directory of your choice and execute it.

Please download the jar file and test it to make sure it runs on your Mac or Linux system, BEFORE you buy the license key.

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3.5 The button "Start AstroViewer" does not appear at the upper left. What can I do?

AstroViewer Online should appear on the page "Interactive night sky map" at the upper left side. It is a button saying "Start AstroViewer". It might take 15 to 20 seconds to load.

Make sure that JavaTM is enabled in your browser.

Make also sure that you have installed JavaTM version 1.4 or higher. Firefox 3.6 or higher requires JavaTM 6 Update 10 or higher. Check here your installed JavaTM version. The latest JavaTM version is available here.

In many cases it helps just to reload the page containing AstroViewer Online.

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3.6 The AstroViewer Online applet gets blocked by the Java security settings. What can I do?

The latest Java (starting with 7u51) has high default security settings.

If you still trust my website you can add it to a "whitelist" within the Java runtime environment, which allows it to run the AstroViewer Online applet.

    Follow these steps:
  1. Click Start -> Programs -> Java -> Configure Java
    Now the Java Control Panel opens.
  2. Select the tab "Security"
  3. Click the button "edit site list"
  4. Click the button "add", enter http://www.astroviewer.com and click the button "add"
  5. Click the button "continue" in the upcoming dialog window
  6. Click OK
  7. Click OK

Now the AstroViewer Online applet should run in your browser.

Find more details and help on this procedure on:
http://www.java.com/en/download/help/jcp_security.xml
http://www.java.com/en/download/faq/exception_sitelist.xml

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