Exoplanets and the stars that host them fascinate both the public
and astronomers mainly because of the (low ?) probability that they
could host life.
The number of exoplanets identified continues to rise rapidly, detections
being made principally by the transit and radial velocity methods. The
database of known exoplanets is available on the internet in 'The
Extrasolar Planets Encyclopedia' at
http://exoplanet.eu/ , this contains details of all the known
exoplanets. If you want to look at these through a telescope or just see
where they are on the sky one can type in the co-ordinates of each planet
but that can be hard work particularly if you want to show your friends or
the public a number of stars hosting exoplanets.
Rather than typing in each planet co-ordinates or compiling your own
database which will need updating as new discoveries are added the Virtual
Observatory offers an easier option. I already have some pages that show
how to connect your telescope to the Virtual Observatory for instance the
page at http://www.johnmurrell.org.uk/AVO-CdC.htm
describes the basics. In this page I look at the specifics of how to
connect the Extra Solar Planets database to
Cartes du Ciel (CdC) which is a Planetarium Programme that can be used to
control your telescope but also can accept information from the Virtual
It is not possible to connect the
Extra Solar Planets database directly to CdC as the website only allows
the complete table to be broadcast, in this case we need to be able to
select the appropriate exoplanet location to send to CdC and thus allow
the telescope to move to the correct position on the sky. To select the
appropriate exoplanet we will use TopCat (
) as has been used in some other examples on this site. The data will be
passed from the Extra Solar Planets database to TopCat and then from
TopCat to CdC using the SAMP (Simple
Application Messaging Protocol) hub and protocol. The details of
how this works should be seamless as long as your PC is connected to the
The first operation is to open
TopCat either from the website above or from your computer if you have
downloaded a local copy. This is done first as TopCat supplies the
SAMP hub that enables the connection between the various VO
Stage 2 is to open the Extra
Solar Planets catalogue at
http://exoplanet.eu/catalog/ , when the page opens the header
should show something like this:
At this point the VO Connection
line will show as 'Off' you need to click the on box that should
result in the line changing to show the TopCat icon to indicate it is
now connected to TopCat via the SAMP hub. You might need to authorize
this connection depending on your PC's security settings.
The next step is fairly obvious
- click the 'send table' button. The TopCat load new table window
should pop-up and after a few seconds the table should automatically
Next open CdC (you might need
to install it first if you have not used it before). CdC does not
automatically connect to the SAMP hub - this has to be done using the
'File - SAMP - Connect to SAMP hub option'.
Next go to the TopCat main
window - it should be open but minimized. On the main window select
the 'Broadcast Row' tick box and then click the 'Activation Action'
button. Another menu will pop-up from here select the 'Transmit
Coordinates' radio button, also select the Target Application as 'skychart'
( the real name for CdC), this prevents the broadcast row being sent
back to the webserver (Astro Tools) which may confuse it. Finally
click Ok to set the activation action. Your TopCat window should now
show: Though the number of rows and
possibly columns may have increased
The next step is to open the
data table in TopCat by clicking on the 'Display Table Cell Data'
button on the main window. You can now scroll down until the Exoplanet
you are interest in is shown, clicking on the row should result in the
display in CdC moving to the appropriate position and if you have it
connected to your telescope this should also slew to the same
If you want to sort the data
table in a particular order this is done via the TopCat main window.
This window allows you to select only certain items to be shown in the
table by creating a 'sub-set'. Instructions on how to do this are in
the TopCat help files and in the documentation on the TopCat website.
You can also create sub-sets by plotting the data in TopCat and then
selecting part of the plot - useful to show objects in a particular
part of the sky or with other specific characteristics.
The SkyPlot is quite interesting
you can see the Kepler detections very clearly - you can even see the
area covered by the CCDs ! ( see the notes below)
That's it - it's far easier and
quicker to do than to describe !
The transmission of information from a webpage to an application using
SAMP is a piece of VO technology that is not used. The Extrasolar Planets
Encyclopedia uses AstroTools (https://github.com/AnotherOneAckap/AstroTools)
which is a wrapper around sampjs below.
web page table transmission technology is not used that often perhaps
the largest application is to transmit catalogues downloaded from
With Vizier this only downloads the number of Rows set by the max
parameter under preferences (default is 50 rows). The extra solar
planets encyclopedia downloads the entire (filtered ?) database with
no limit on lines.
The transmission of the information used the tool sampjs (
http://astrojs.github.io/sampjs/ ), this page has a number of
examples which might help if you want to use this on your own web
pages. A search will show some other similar tools including some that
are wrappers around sampjs.
Plotting the position of the exoplanets on the sky using TopCat shows
the Kepler field quite well, about 2/3 of the exoplanets were
discovered using Kepler.
interesting exercise is to use TopCat to colour the planets by mass, a
tip is that you probably need to hide the points without mass
otherwise they overwhelm those with mass values. Also a logarithmic
colour scale helps as there is a wide range of masses - which is the
smallest and largest ?
Instead of or as well as sending the location of the exoplanets to CdC
you can send the data to Simbad for a more detailed view of the sky
and the objects in the vicinity of the exoplanet. In section 6 you
either need to select Aladin as the destination or select all in which
case it will be sent to CdC and Aladin.
New - 22/1/2017 The Exoplanet
Encyclopedia has a page on using the Encyclopedia with the virtual
observatory at http://exoplanet.eu/vo/
. This has links to two pages one to produce
simple plots and one to produce
more advanced graphics. Both
of these use TopCat to produce the plots and are worth looking at even
if it is to see what is possible.
John Murrell 2017