# Will I be able to see both Jupiter and Saturn at the same time in my Astromaster 114?

I have a Celestron Astromaster 114 Newtonian reflector telescope. The specs:

• aperture: 114mm
• focal length: 1000mm
• focal ratio: f/8.77

I also have a t-ring so I can connect a Nikon camera to it.

Will I be able to see both Jupiter and Saturn at the same time thru this telescope? I understand from this article that they will come within a tenth of a degree of each other. The article says this is "fifth of the width of the full moon" which, based on my experience, suggests that I will indeed be able to see both, but I'm hardly any expert.

I'm considering borrowing a friend's film camera to try and snap a photo of both in one image, but would like to avoid the trouble (thanks, COVID!) if this won't happen.

• I've added another answer. It's usually a good idea to refrain from accepting an answer for a few days at least. There are several astrophotographers here but they don't necessarily check in every day.
– uhoh
Dec 18 '20 at 1:37

This can easily be tested using software such as Stellarium, where you can visualize the field of view with given focal length.

If you have the software installed, click on "ocular view" (the most left button in the upper right corner). The following view is what you culd expect on December 21 with a 10mm eyepiece and a focal length of 1000mm:

And this is the view when attaching a Crop-sensor (APS-C) Camera to a telescope of focal length 1000mm:

So you should be able to see both planets and some moons in your telescope.

Some notes:

• These simulated views do not necessarily represent the actual view to 100% accuracy. I did leave the "atmosphere" setting turned on, but actual visibility and brightness will depend on your location (light pollution and other atmospheric effects such as haze might reduce visibility)

• Because I was lazy, I used the default telescopes and eyepieces. This ignored aperture (or rather, it was different than on your telescope), but it won't have an effect on magnification. If you wanted, you could add your own telescope in the software's settings.

• Thanks, @jonas, for this great answer. Dec 17 '20 at 21:36

### Direct viewing through an eyepiece

When looking through an eyepiece, there is an apparent field of view. This answer says:

Because I was lazy, I used the default telescopes and eyepieces.

which means that the circles shown are what one would see if one had an eyepiece with a field of view equal to the default eyepiece used in the Stellarium simulation. If your eyepieces have a narrower apparent FOV then the circle should be drawn smaller.

The actual FOV is the apparent FOV divided by the magnification.

SO if you have f=1000 mm and a 10 mm eyepiece you have 100x magnification. If your actual eyepiece has an apparent FOV of 50 degrees then your actual FOV is 0.5 degrees or 30 arc minutes.

Just recently they have become closer than that so from now until the end of December you would be able to see them with the eyepiece I've just described.

The FOV of your camera's sensor is a totally different issue!

It is rectangular not circular, and so you may have to rotate your camera body around the axis of the telescope to get the long direction or the diagonal direction parallel to the line between the two planets.

Your camera's documentation will give you the CCD sensor's dimensions in millimeters.

Let's say it's h x w = 4mm x 6mm. Assuming there are no lenses in between and your Newtonian telescope's primary mirror's focus is directly on the sensor, the FOV of your sensor is h/f x w/f or 4/1000 x 6/1000 radians. Multiply by $$180 / \pi$$ to get degrees, so it will be 0.23 x 0.34 degrees, a lot smaller than for an eyepiece!

Diagonally it's $$\sqrt{(w/f)^2 + (h/f)^2}$$ or 0.41 degrees.

Since your sensor will be a different size:

• @S.Imp Great, thanks! I got a notification for your comment here because it's my post and because I've already commented here, which is good because I didn't get a notification for your other comment because it's not my post nor have I commented yet there. For more on how all of that works go to Stack Exchange FAQ and then click How do comment @replies work?