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How I captured the James Webb Space Telescope (A quick guide to use NASA Horizons System tool)

From the moment JWST launched on December 24, I was thinking of capturing it while it was on the way to L2 point. Unfortunately, here, a clear night in December is rare! But finally, in the third attempt, the weather forecast came true, and I could capture it. Yay!

After I published the video on my social media, I was asked how I found it in the sky several times, so I decided to explain it here and give you some tips, so you can image JWST too, or use these steps for other solar system objects in the future. The tool I used to find the coordinate was NASA Horizons System. This tool is provided by the Solar System Dynamics Group of the JPL, and it can generate ephemerides of many solar system objects, including planets, asteroids, comets, some spacecraft, etc.

Now, let's cut to the chase.

Go to and click on the app tab

Make sure the Ephemeris Type is on the Observer Table

Then click on Edit on the second row to choose your target (here, James Webb Space Telescope)

Now specify your location on the third row.

There are several ways to do this, but I suggest you specify the coordinates for better accuracy. Make sure the Type of coordinates is Geodetic Coordinates.

A simple way to find your exact coordinate is to use Google Earth. Find your location and use the coordinates and altitude on the bottom right of the screen. For latitude, use a positive number for north and a negative for the south. Also, keep in mind that you should use a negative number for west longitude.

Then specify the period on the fourth row. Here, time should be in UTC.

To find the UTC, you can use timeanddate website. Add your city here and enable Include UTC Time in Results.

You don't have to change the fifth row. Now click on Generate Ephemeris. Then scroll down to see something like this. This is what you're looking for.

Now you can use your mount's GoTo or a software with plate-solving feature to slewing to those locations. Depending on your mount, it may accept the J2000 or JNow frame in most cases. The ephemeris we generated before was in the ICRF frame. ICRF and J2000 frames are very similar, so we can say they are the same for our purpose. As a result, if your mount accepts the J2000, you can use the ephemeris coordinates, but if you need the JNow coordinate, you can use Stellarium to find it, and I'll explain it here. But first, I want to show you how to find those coordinates in Stellarium to have an idea of where it is.

Finding the object location in Stellarium

First, to make the process easier, open Configuration Window and enable Pointer Coordinates and restart the Stellarium. You'll see and new icon at the bottom.

Now, enable it and right-click on it to open its preferences window and make sure the Coordinates is on the Right ascension/Declination (J2000.0).

Then save it and close it. Now, when you move the cursor on the map, you can see the coordinates on the top right corner of the screen.

(Optional) Again, open Configuration Window, go to the Extras, and enable ICRS grid. You'll see a new icon on the bottom ribbon. Enable it to help you find the coordinates.

With the help of these two new tools, you can find the exact coordinates easily. In addition, you can hold the shift key and click to mark that location when you find it.

If you need the JNow coordinates, simply change the Coordinates to Right ascension/Declination, then move the cursor to the marked location and see the new coordinates.


In the end, I want to show you the accuracy of this method. This is the image I took of JWST.

Based on my ephemeris, its location should be 06 17 00.15 +00 12 32.6.

I ran ImageSolver on the image, and the result was 6 16 59.973 +0 12 31.52, which is very close to the predicted coordinate.


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4 comentários

15 de fev. de 2022

Here is a handy link that will give you the ephemeris quickly and is very user friendly:


10 de jan. de 2022

Thank you!


10 de jan. de 2022

Excellent! Thanks for sharing


10 de jan. de 2022

Thank you for this helpful post!

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