WWT Data Blog

Sticking images on the sky with WWT

dinos — Thu, 27 Nov 2008 05:48:20 GMT

Suppose you have a photograph of a small part of the sky, and you want to see it in WWT and share it with friends. Here’s how you can do so.

We assume that the image (and, if you wish, a thumbnail) is already internet-accessible.

All you need to do is use the url below, with a few parameters. This is from information provided by Jonathan Fay, the architect/developer of WWT.

Base URL:

http://www.worldwidetelescope.org/wwtweb/ShowImage.aspx?

URL Parameters:

You require the following parameters. All strings are URL encoded – spaces replaced by %20 or +, etc.

name = {string: URL encoded, user friendly, but relatively unique name }
ra = {double: right ascension of image center (or tangent point) from plate solution}
x = {double: pixel position corresponding to the ra above}
dec = {double: declination of the image center {or tangent point) from plate solution}
y = {double: pixel position corresponding to the dec above}
scale = {double: arc seconds per pixel from plate solution}
rotation = {double: rotation east of north}
imageurl = {string: URL encoded link to original image at the scale and size of the image described in the rest of the URL}

While the following parameters are optional:

thumb = {string: URL encoded href to thumbnail image (Should be 96x45)
credits = {string: Text for credits }
creditsUrl = {string: URL encoded link to credit information or image page }
reverseparity = {Bool: True or False (default to false) for image flip } .

PS: reverseparity=true is implemented in a not-yet-released version of WWT. So if you have a flipped image, flip it first for now.

When you are testing, the following parameters could be useful:

goto = {Bool: True or False (default to false) True: Slew and Zoom on Image only, False: Show Image Thumbnail in Open Collections, user must click thumbnail to Slew and Zoom and can save image to collections}
debug = { Bool: True or False (default to false) shows the WTML instead of launching it }

For an example of something really cool that you can do with this, have a gander at Christopher Stumm’s post on the astrometry flickr group. Any image uploaded to that group gets solved by the astrometry.net solver. Chris added a feature whereby the format above is used to display these solved images in WWT. So members of that group can see their images in WWT (and use them in tours) right now. Nifty, eh?

Let’s use this from scratch, say with today’s APOD image of the Horsehead Nebula.

The results of sending this through astrometry.net to get a solved image are here. The key part of the page is this, as well as the knowledge that the original image was 900 x 600 pixels.

And if you click on the url below, you’ll get to the image on WWT.

http://www.worldwidetelescope.org/wwtweb/ShowImage.aspx?name=Horsehead+APOD
&ra=85.2983&dec=-2.42589
&scale=1.69&rotation=90.21
&imageurl=http://antwrp.gsfc.nasa.gov/apod/image/0811/horsehead_caelum.jpg
&x=450&y=300
&creditsUrl=http://antwrp.gsfc.nasa.gov/apod/ap081126.html
&credits=Adam+Block,+Mt.+Lemmon+SkyCenter,+U.+Arizona
&thumb=http://research.microsoft.com/~dinos/wwtimages/tn_horsehead_caelum.jpg

This method works for small and medium sized images. For large images – over 2048 x 2048 pixels, say - you will want to tile that and use a WTML file for it.

There are other interesting things you can do with this. The image you place doesn’t have to be a picture of the sky. For instance, here’s a constellation image – the crown for the Corona Borealis - from the Hevelius collection digitized and put online by the U.S. Naval Observatory and the Space Telescope Science Institute. With some adjustment (making the non-transparent areas white instead of black), this can be placed online and viewed in WWT by clicking on the link below.

http://www.worldwidetelescope.org/wwtweb/ShowImage.aspx?name=Crown
&ra=236&dec=28.894&x=250&y=217&scale=60&rotation=180
&imageurl=http://research.microsoft.com/~dinos/wwtimages/coronawhitesmaller.png
&thumb=http://research.microsoft.com/~dinos/wwtimages/coronatn.jpg

The result looks like this (with crossfade)

Its placement could be improved… but since this is a demo, we’ll leave that as an exercise for the reader.

Did we mention that one can use these in tours?

Making your own WWT Community

dinos — Wed, 19 Nov 2008 22:28:30 GMT

Communities are the primary way in which WWT users can share data and tours with each other. They are made by external individuals or organizations, such as planetariums, science centres, astronomy clubs, magazines, blogs, schools, classes, and class projects. Anyone can create multiple communities.

You can set up your own community using your own servers (we do not yet offer specific storage for this purpose) and have it working using WWT without ever telling us at Microsoft Research about it. Having said that, more people will find your community if you list it on our Community Directory (see a subset of existing communities at the WWT Support page), so send an email to WWTCommunity@microsoft.com if you want your community listed. To be considered for inclusion in the community directory, community sites must maintain standards in terms of quality, scalability, and content appropriateness. These standards include:

Sign-up membership may be required, but community access must remain free for all users.
Community content must be well moderated, free of hate speech, and reflect currently accepted astronomical information/theory.
Must have sufficient capacity for handling projected traffic.
Must make use of integrated WWT features like tours, sky-aligned images, etc. Not just simple HTML links to existing web content.

To set up a community, you should first add the WWT file extensions to the of mime types on your server.

	File Extension	Mime Type
WWT Collections (and Communities)	.wtml	application/x-wtml
WWT Tours	.wtt	application/x-wtt
WWT Constellation Figures	.wwtfig	application/x-wwtfig

Then you need to set up the following files:

Thumbnail for the community. This should be 176 x 45 pixels.
Payload file. This is THE file at the heart of the community, determining its folder structure, etc. It is a WTML file that can link to other WTML files as well. It can be, in its simplest form, a static WTML file that is hand-edited on the server side. It can also be generated from a database so that it is constantly updated. For details on how to create WTML files, see the previous post.
Signup file. This is a short WTML file that points to the Thumbnail and Payload files, and gives the title of the community. Here is the signup file for the WWT Data Community .

  <?xml version="1.0" encoding="UTF-8" ?> 
  <Folder Name="WWT Data Community" 
          Group="Community" 
          Thumbnail=”http://research.microsoft.com/~dinos/wwtdata/wwtdatacommunitylogo.jpg” 
          Url="http://research.microsoft.com/~dinos/wwtdata/wwtdata_payload.wtml" />

And … that’s it All the power of a community is in how you generate the payload file. You can have a Content Management System and databases to generate your payload file automatically, and keep changing it depending on where the WWT application is currently looking, for example. We will provide examples of that in future posts.

PS: Tools to produce your own WTML and image files for studies, panoramas and surveys (as some people have requested in comments on earlier posts) will be released in the next 2-4 weeks. But you can produce your own communities with tours and locations now.

Addendum: Here is a partial list of resources that can be contained in the payload of a community:

Tours
Study Images
Surveys
Panoramas
Lists of locations e.g. observing lists, locations of supernovae found last night, etc. This is just a Place entry without an ImageSet.
Catalog objects
Articles or any other uploaded content e.g. PDFs, Word docs, Excel spreadsheets
constellation figures (that’s what the WWTFIG extension is for)
HTML links e.g. to articles or the organization’s webpages
Blog entries
conversation threads / discussion boards

How WTML files work

dinos — Wed, 19 Nov 2008 21:19:21 GMT

WTML stands for Worldwide Telescope Markup Language. It is one of three file formats native to WWT, the others being WTT files to store tours and WWTFIG to store constellation figures. If you want to host any such files on your servers, you will need to add them to the list of mime types supported by the servers. The entries for those are :

	File Extension	Mime Type
WWT Collections (and Communities)	.wtml	application/x-wtml
WWT Tours	.wtt	application/x-wtt
WWT Constellation Figures	.wwtfig	application/x-wwtfig

WWT also uses the astronomy standard VOTable format from the IVOA (International Virtual Observatory Alliance) to transfer data, but that is another blog post.

WTML files can be used for the following purposes

Storing collections. A collection can be thought of as a hierarchy/tree of folders, each folder contain a mixture of folders and objects (in the same way that a file folder contains a mixture of file folders and files). Objects can be
- tours
- studies. A study is a photograph of a small part of the sky e.g. a Hubble image of the Crab Nebula. The WTML entry for a study does not contain the image itself, but instead
  - the location on the internet (or on your hard disk) where the study is stored
  - Coordinates – how to show the study on the sky
  - Metadata - title, alternative names, credits, etc for the study
- panoramas
- planets
- all-sky surveys
- locations on the sky
The ‘sign up’ file for a community. This points to the collection that defines the holding the data for the community.

Here is an example of a WTML file that defines a collection called ‘Samples’.

The Samples collection has two folders, called ‘Some Tours’ and ‘Some Studies’.

The Some Tours folder has two tours, while the Some Studies folder has two studies.

The structure of the WTML file looks something like this:

<?xml version='1.0' encoding='UTF-8'?>
<Folder Name = "Samples">

  <Folder Name="Some Tours" Group="Tour">
    <Tour Title="Over Mars" . . . />
    <Tour Title="Apollo Missions" . . . />
  </Folder>

  <Folder Name="Some Studies" Group="Explorer" Searchable="True" Type="Sky" Thumbnail="">
    <Place Name="Hubble Scores a Perfect Ten" . . . > . . . </Place>
    <Place Name="Hubble Directly Observes Planet Orbiting Fomalhaut" . . .> . . .</Place>
  </Folder>
</Folder>

The Folder tags determine the structure of the hierarchy. The tag can have several attributes. Group is usually set to “Explorer”; it is set to “Tour” for a folder of tours. It can also have a thumbnail by setting the Thumbnail attribute to the location of a 96 x 45 image on the web. If no thumbnail is provided, the standard folder thumbnail is used. Searchable should be set to “True” (not “true" since case is important) for folders with studies so that they can be found using WWT’s search mechanism. Type is set to “Sky” for studies – its other possible values are “Planet”, “Panorama” and “Survey” (covered in future examples).

The Tour tags contain entries for tours.

The Place tags contain entries for studies (‘places on the sky’).

Now, here is the full file. You can also get to it from here: wtml , txt .

<?xml version='1.0' encoding='UTF-8'?>
<Folder Name ="Samples">

<Folder Name="SomeTours" Group="Tour">
    <Tour Title="Over Mars"
         ID=""
         Description="A trip to Mars"
         Author="Dinoj Surendran"
         OrganizationName="Microsoft Research"
         AuthorImageUrl="http://research.microsoft.com/~dinos/live2eat_tn.jpg"
         ThumbnailUrl="http://research.microsoft.com/~dinos/wwtexp/overmars_tn.jpg"
         TourUrl="http://research.microsoft.com/~dinos/wwtexp/marsTake11.wtt"
         LengthInSecs=”258” />

    <Tour Title="Apollo Missions"
         ID=""
         Description="Brief history of Apollo missions"
         Author="Dinoj Surendran"
         OrganizationName="Microsoft Research"
         AuthorImageUrl="http://research.microsoft.com/~dinos/live2eat_tn.jpg"
         ThumbnailUrl=”http://research.microsoft.com/~dinos/moony.jpg”
         TourUrl="http://research.microsoft.com/~dinos/moony.wtt"
         LengthInSecs=”243”
         OrganizationUrl=”http://research.microsoft.com”
         AuthorEmail=”dinos@microsoft.com”
         AuthorUrl=”http://research.microsoft.com/~dinos”
         Keywords=”Apollo;Moon” />
</Folder>

<Folder Name="Some Studies" Group="Explorer" Searchable="True" Type="Sky" Thumbnail="">

    <Place Name="Hubble Scores a Perfect Ten"
          DataSetType="Sky"
          RA="3.18858333333333"
          Dec="1.31471944444444"
          ZoomLevel="0.2"
          Opacity="100"
          Constellation="CET">
      <ForegroundImageSet>
        <ImageSet DataSetType="Sky"
                 BandPass="Visible"
                 TileLevels="3"
                 Url=http://research.microsoft.com/~dinos/wwtexp/530919080/{1}/{3}/{3}_{2}.png
                 CenterX="47.828862896748753"
                 CenterY="1.3146065774006597"
                 Rotation="-5.0799999999999867"
                 BaseDegreesPerTile="0.02842076047738"
                 FileType=".png"
                 WidthFactor="2"
                 Projection="Tangent">
          <Credits>NASA, ESA, and M. Livio (STScI)</Credits>
          <CreditsUrl>http://hubblesite.org/newscenter/archive/releases/2008/37/</CreditsUrl>
          <ThumbnailUrl>http://research.microsoft.com/~dinos/wwtexp/530919080.jpg</ThumbnailUrl>
        </ImageSet>
      </ForegroundImageSet>
    </Place>

    <Place Name="Hubble Directly Observes Planet Orbiting Fomalhaut"
          DataSetType="Sky"
          RA="22.9608472222222"
          Dec="-29.6222361111111"
          ZoomLevel="0.123333333333333"
          Opacity="100"
          Constellation="PSA"
          Classification="Unfiltered"
          Magnitude="0"
          Distance="0"
          Rotation="0"
          Angle="0"
          AngularSize="1">
      <ForegroundImageSet>
        <ImageSet DataSetType="Sky"
                 BandPass="Visible"
                 TileLevels="4"
                 Url=http://research.microsoft.com/~dinos/wwtexp/934203617/{1}/{3}/{3}_{2}.png
                 CenterX="344.412708333333"
                 CenterY="-29.6222361111111"
                 Rotation="0"
                 BaseDegreesPerTile="0.0220985710119568"
                 BaseTileLevel="0"
                 FileType=".png"
                 WidthFactor="2"
                 Sparse="True"
                 QuadTreeMap=""
                 Projection="Tangent"
                 Name=""
                 BottomsUp="False"
                 OffsetX="0"
                 OffsetY="0">
          <Credits>NASA, ESA, P. Kalas (UC Berkeley) et. al.</Credits>
          <CreditsUrl>http://hubblesite.org/newscenter/archive/releases/2008/39</CreditsUrl>
          <ThumbnailUrl>http://research.microsoft.com/~dinos/wwtexp/934203617.jpg</ThumbnailUrl>
        </ImageSet>
      </ForegroundImageSet>
    </Place>
</Folder>
</Folder>

Let’s now have a look at the individual entries in closer detail. First, tours.

   <Tour Title="Over Mars"
         ID=""
         Description="A trip to Mars"
         Author="Dinoj Surendran"
         OrganizationName="Microsoft Research"
         AuthorImageUrl="http://research.microsoft.com/~dinos/live2eat_tn.jpg"
         ThumbnailUrl="http://research.microsoft.com/~dinos/wwtexp/overmars_tn.jpg"
         TourUrl="http://research.microsoft.com/~dinos/wwtexp/marsTake11.wtt"
         LengthInSecs=”258” />

There are other attributes that the Tour element can have, some of which are shown in the entry for the Apollo tour, but these are the ones that control how the tour is displayed. (See picture below.) Most of this information would have been entered in the Tour Properties panel when you made the tour, so you might be wondering why you are being asked to enter it again. That is because your tour may not have been downloaded by the WWT user by the time she sees the information in the panel about the tour. So this entry is not just an entry for your tour, but an advertisement for it. Therefore, make your Description of it much more appetizing than the one used in this example!

Title is the name of the tour.
Author is the name of the tour creator.
OrganizationName is the name of the institution, if any, that the author is making the tour for. Set to “” if it is not applicable.
ID must be supplied… as an empty string “” for now.
Description is a description of the tour. It can also include credits e.g. whose music or narration or images were used.
TourUrl points to the location on the web where the wtt file containing the tour.
ThumbnailUrl points to a 96 x 45 thumbnail for the tour. The white ‘T’ in the top right is added automatically by WWT; you do not need to put it in.
AuthorImageUrl points to a 72 x 96 thumbnail of the author, a picture that is typically more recent than the one used in the example here.
LengthInSecs is the duration of the tour in seconds. The world will not explode if it is incorrect.

Now that you know enough about WTML entries for tours, let’s consider WTML entries for studies.

Study images are stored in image pyramids. Given a H x W pixel study, we represent it as a N x N pixel image where N is the smallest power of 2 that is at least as big as H and W. In other words, N = 2^ceiling(log_2(max(H,W))). The extra area not covered by the H x W photograph is occupied by transparent pixels. This forms the lowest level of the pyramid, with each next level contains a lower-resolution version of the original image with each level’s image having half the height and half the width as (i.e. four times smaller than) the image in the previous level. At each level, the image there is chopped up

For example, suppose we had a 1457 x 1201 study image, such as this Spitzer image to the right. We embed it in a 2048 x 2048 image and store it in a pyramid with four levels 0, 1, 2, 3. (Note: Number of Levels = 1 + Maximum Level)

At level 3 are 64 (=8 x 8) 256x256 tiles that partition the 2048 x 2048 image.
At level 2 are 16 (=4 x 4) 256x256 tiles representing a downsampled 1024 x 1024 version of the image. Here they are, with the grey shadows showing the transparent regions. Some of the tiles have been labelled with X and Y coordinates between 0 and 3 inclusive as well. That is how we access individual tiles of the pyramid, specifying its (X,Y) coordinates within the 2^L x 2^L grid of tiles at level L.

At level 1 are 4 (=2 x 2) 256x256 tiles representing a further downsampled 512 x 512 version of the image.

At level 0 is a downsampled 256x256 version of the image, as shown below.

The WTML entry for this study is below. Its location is about Right Ascension = 47.83 degrees (3h 11m 19s) and Declination 1.32 degrees (1d 18m 53s) in J2000 coordinates, and it is about 20 arcseconds wide.

    <Place Name="Hubble Scores a Perfect Ten"
          DataSetType="Sky"
          RA="3.18858333333333"
          Dec="1.31471944444444"
          ZoomLevel="0.2"
          Opacity="100"
          Constellation="CET">
      <ForegroundImageSet>
        <ImageSet DataSetType="Sky"
                 BandPass="Visible"
                 TileLevels="3"
                 Url=”http://research.microsoft.com/~dinos/wwtexp/530919080/{1}/{3}/{3}_{2}.png”
                 CenterX="47.828862896748753"
                 CenterY="1.3146065774006597"
                 Rotation="-5.0799999999999867"
                 BaseDegreesPerTile="0.02842076047738"
                 FileType=".png"
                 WidthFactor="2"
                 Projection="Tangent">
          <Credits>NASA, ESA, and M. Livio (STScI)</Credits>
          <CreditsUrl>http://hubblesite.org/newscenter/archive/releases/2008/37/</CreditsUrl>
          <ThumbnailUrl>http://research.microsoft.com/~dinos/wwtexp/530919080.jpg</ThumbnailUrl>
        </ImageSet>
      </ForegroundImageSet>
    </Place>

Let’s start with the ImageSet tag first.

DataSetType should be set to “Sky” since this is a study.
BandPass refers to the primary wavelength in which the image was taken. This is not used much by WWT, and only allows one wavelength to be stored (even for composite images). The possible values are (case-sensitive) Gamma, XRay, Ultraviolet, Visible, HydrogenAlpha, IR, Microwave, and Radio.
TileLevels is the maximum level of the image pyramid used to store the study. This study uses 4 levels numbered d 0 to 3, so TileLevels is 3.
Url is a url that returns a 256 x 256 tile of a specific part of the image pyramid. In this case, it is a path to an image on the web, but it can be any url (e.g. a SQL query) that contains {1}, {2}, {3} in it for L (level), X, and Y respectively. For example, if L is 2, X is 0 and Y=3, this would be http://research.microsoft.com/~dinos/wwtexp/530919080/2/3/3_0.png
FileType is the extension of the files – either .jpg or .png . Remember to include the period. (And if you must use JPEG, please use 100% quality for everyone’s sake!)
CenterX : Right Ascension of the center of the image
CenterY : Declination of the center of the image
Rotation: Angle at which image is inclined
BaseDegreesPerTile : Right, now this is not intuitive… though it is well defined. This is the number of degrees of declination that the top tile of the pyramid occupies on the sky. Alternatively, remember how we embedded each study in a larger 2^n x 2^n image? This is also the number of degrees of declination that that larger image occupies on the sky. In this case, our 1457 x 1201 study is about 1 arc minute high. Multiply that by 2048 / 1201 and you get 0.0284… degrees
Project : Always set this to Tangent for studies since studies are tangentially projected.
WidthFactor : Ignore what this actually means and just set it to 2. It’s some technical detail, some WWT historical tidbit that is more gory than glory.

Credits: Brief description of where the image came from, who made it, etc.
CreditsUrl: Where you can get more information on the image
ThumbnailUrl: A link to a 96 x 45 image with a thumbnail for the study.

Right, so that defines how the image is set on the sky. The rest of the Place tag looks like this:

This defines how the image is viewed on the sky. You know how in WWT when you double/click on a study thumbnail it takes you there? The RA, Dec, and ZoomLevel entries determine the viewpoint where you zoom to.

Name : The title of the study. Alternate names can be included; just separate them using semicolons.
RA : Right Ascension, in hours, of the center of the viewpoint for the study. You usually want this to be the center of the image. For historical reasons, this is between 0 and 24 hours, so we divided the RA of the image (CenterX) in the ImageSet tag (which is between 0 and 360 degrees) by 15.0.
Dec : Declination, in degrees, of the viewpoint for the study. Here it equals CenterY.
ZoomLevel : Height of the viewpoint in degrees.
DataSetType : Set to Sky.
Opacity : Set to 100.
Constellation : Determines constellation shown in the Study Properties panel. Set to the three-letter code (see here for list) of the region of sky where the study is. No kittens will die if you set it to an arbitrary value such as “AND” for Andromeda initially and correct it later.

There are other details we have not mentioned, such as how (CenterX,CenterY) are really the coordinates of the reference pixel of the image that is defined by fields called OffsetX and OffsetY. Their default settings of OffsetX=OffsetY=0 cause the reference pixel of the image to be its center. Another one is Classification, which defines what kind of study it is (case-sensitive choices are listed here), the default being Unfiltered, which means it has not been filtered into a category yet.

But this should be enough to get you started.

WWT Data Communities (including an improved DSS background!)

dinos — Mon, 17 Nov 2008 04:18:04 GMT

W always have more data in the works that has yet to make it to the main WWT datasets. If you would like to have a look at them, join these two communities.

To join the WWT Data Community, click here ! The datasets in here are as reliable as other datasets in WWT - you can use them in tours without fear that their storage location will change in the near future.

The initial datasets available in the WWT Data Community are the following:

A first attempt to smooth out the Digitized Sky Survey using modern blending techniques. While we cannot yet provide full details on how this was made or by whom, the SphereStitch project page does provide some details. The screenshots below are from there - the left is the existing background while the right has the processed version. And yes, there will be more work on this - what you see here is only the beginning. And yes, we know about the need to flat-field it.

The Near-UV and Far-UV versions of the GALEX Release 2/3 data. WWT currently displays the combined version. We are currently, thanks to folks at the Space Telescope Science Institute and at NASA SkyView, working on processing GALEX 4.
The panoramas from the Denver Museum of Natural History by DMNS Curator Kachun Yu. We blogged about this in a previous post.

Owing to the way our team is structured, we also have some datasets that are new and useful but whose storage cannot be relied on to continue. (In other words, use them as storage at your own risk!) Datasets hosted here will eventually move to the main WWT Data Community once their storage has been stabilized. But to see the latest data processed by us, join the WWT Data Experimental Community. Currently it has the latest press releases from the Hubble Space Telescope and top-level TOAST tile boundaries for sky and planet views.

WWT Tips 1

dinos — Sat, 15 Nov 2008 18:03:00 GMT

Here are, in no particular order, some tips for WWT users. (PS: Anyone seen the new tours that went up this week, for WALL-E, the first pictures of extrasolar planets, and a farewell to the Phoenix Lander?)

Q: How can I slow down the way WWT zooms?

A1: Press SHIFT while zooming.

A2: Set the Zoom Speed in the Settings panel.

Q: My mouse is dead / missing / visiting relatives. How do I zoom?

A: Use Page Up / Page Down. You can also use + and –. Or an Xbox controller or 3d navigator.

Q: Help! I’ve been playing tours and now I’ve lost my menus!

A: In the Equinox Release, WWT plays tours in full-screen mode. To enter or leave full screen mode, press F11.

Q: How do I quit a tour midway?

A: Press ESC. You may also wish to press F11 to leave full screen mode.

Q: I’m making a tour, and I shoved an object to the top/bottom of the screen and now I can’t pick it to modify it! Those darned panels keep getting in the way!

A1: Use the TAB key to choose between selected objects in a tour slide.

A2: Uncheck the Transparent Tabs box, like this.

Q: I want to use WWT to go to a bunch of specific locations in the sky. However, my list of points are all in Galactic coordinates, not the J2000 coordinates that WWT uses. What do I do?

A: Select a different coordinate system while searching. Note that your current location will still be displayed in J2000 coordinates.

Q: How can I search for the Pled Plead Plied Pl… how can I search for something I can’t spell?

A: When you type something in the search box of WWT, you do not have to type in the full name of what you are searching for. In this case, you just have to enter ‘ple’ before they Pleiades show up in your results.

Q: I am used to other programs where you zoom in onto where the mouse is pointing, and I find WWT’s zooming mechanism confusing.

A: Get used to it. It’s cooler this way.

Q: Maybe so, but my brain is hard-wired to center-zoom on where my mouse clicks.

A: Check the Zoom On Mouse box in Settings.

Q: How can I see the Virtual Earth datasets at higher resolution?

A: Turn off elevation in the Settings panel. (And yes, this is a temporary work-around.)

Q: How do I see what the sky looks like in my current location?

A: To change your location, click on the Setup button under Observing Location in the View tab. Then check ‘View from this location’ to get the horizon inserted.

Q: Oh no! Half my screen is blue!

A: That’s the horizon. You must have the View From This Location check box checked. Uncheck it.

Q: My telescope is not in WWT’s list of telescopes, and it is not amused.

A: Enter your own telescope and camera in the magic file that controls this:

Vista: “c:\Users\<userid goes here>\AppData\Local\Microsoft\WorldWide Telescope\data\Instruments.xml”

XP: “C:\Documents and Settings\<userid goes here>\Local Settings\Application Data\Microsoft\WorldWideTelescope\Instruments.xml”

Like other data files, WWT will update this file on your hard disk when we update the same file on our Redmond servers. Make sure that you make a copy of your edited file in a different directory so that you can re-edit instruments.xml when an update happens. (Better, you can also send us an email with your edit so we can include it in our future updates.)

Q: My location isn’t on your list of locations, and I am not amused.

A: Enter your location name, latitude, longitude and altitude anywhere (including the first entry so you can see it faster) in the magic file called World Cities.txt that controls this.

Vista: “c:\Users\<userid goes here>\AppData\Local\Microsoft\WorldWide Telescope\data\places\World Cities.txt”

XP: “C:\Documents and Settings\<userid goes here>\Local Settings\Application Data\Microsoft\WorldWideTelescope\places\World Cities.txt”

If your location is in the USA or Canada, you should, theoretically, edit one of the other files, e.g. WA.txt for Washington or QC.txt for Quebec. But that is entirely up to you, as this file only affects you.

Incidentally, the tab-separated file looks something like this (and yes, this file does have entries from Ireland and Costa Rica…)

Like other data files, WWT will update this file on your hard disk when we update the same file on our Redmond servers. So keep a copy of your edits.

Q: Oh no! I’m lost! What do I do now?

A: WWT has a ‘Home’ command – select the Reset Camera in the View tab.

Q: I can’t see any images at all! Just constellation lines.

A: If your video card is up to par, this is most likely a network issue. Enter your proxy server in the Network and Cache part of the Settings tab.

Incidentally, most of the Solar System mode works fine without a connection to the internet.

Q: WWT seems to be stuck with downloading tiles. My internet connection is fine. What do I do?

A: Go to the part of the sky where the problem is (chances are, you are already there), and press F5. That refreshes the screen. If that fails, press CTRL+F5. That not only refreshes the screen, but also redownloads all tiles for that part of the view from the internet. (When WWT fails to download a tile, it does not try to do so again as it assumes the tile does not exist.) If you think the problem is affecting your entire cache for that dataset, right click on the dataset’s thumbnail and choose ‘Remove From Image Cache’ and then start browsing again.

Also note – particularly when on a slow internet connection - that you can see what tiles need to be downloaded by choosing Settings->Advanced->Show Download Queue.