Success Story: Getting a Photo of the James Webb Space Telescope from Half a Million Miles Away

James Webb Space Telescope (NASA)

The James Webb Space Telescope (JWST) is the most powerful telescope yet developed. Its primary mirror is 6.5 m in diameter, with 6 times the light-gathering ability of Hubble. It is expected to see light that originated 100 million years after the Big Bang, when the first galaxies were forming.  Earth’s atmosphere would prevent JWST from doing this, so it will operate in the vacuum of space, at a point 1 million miles from Earth. It launched on December 25, 2021. 

On January 3, 2022, when JWST was passing through a point halfway to its destination, I had an evening of clear skies and decided to try something daunting: to capture a photo of JWST from its home planet.  I’m an amateur astrophotographer; although I have been keenly interested in astronomy and cosmology for most of my life, I got serious about shooting photographs of Things in Space™ a little more than a year ago. As a life-long photographer I had lots of experience and high-quality photographic equipment—I thought astrophotography would be simple.  Wrong.  It is an entirely different game compared to regular photography.  All of the equipment I use for my astrophotography was newly purchased in 2021. My equipment is described in some detail in a note at the bottom.

Several challenges had to be met in reaching my goal of capturing an image:

  1. Finding JWST. The space telescope does not have its own source of light; it doesn’t glow. It reflects light from the Sun, and at its current distance it is reflecting very little. It is a dim object, way below the power of the unaided eye to detect. You cannot simply look up and see it, you must know where in the sky to aim a telescope that can collect enough of the dim light that it is reflecting to make it visible. Fortunately I found a list of the hourly location of JWST that allowed me to point my telescope in its direction. 
  2. Collecting enough imaging data. JWST is a dim object that will appear among much brighter stars. I shot 60-sec exposures in the hope that this would allow me to collect enough of its reflected light to make the dim object visible. The Earth is rotating, so a perfectly stable camera focused on the heavens will result in an image in which the stars blur as they sweep across the sky. With the telescope that I used any exposure longer than 1 sec would result in obvious “star trailing.” Astrophotography requires a camera mount that rotates in a manner that compensates for the Earth’s rotation. My mount has allowed exposures as long as 2 min when I have it properly aligned with the Earth’s axis; additional equipment can monitor slight movement of stars relative to the field of view and make ongoing adjustments, allowing exposures as long as 6 – 10 min (I do not yet have this capability). 
  3. Differentiating JWST from the stars. Even if I use an exposure that makes the dim JWST visible, it will look exactly like a very dim star.  It will be recognizable as a craft hurtling through space only because its location will change relative to the constant background stars.  To see this change, multiple sequential exposures are needed. I shot 180 60-sec images, hoping that this would be sufficient to allow the movement of a very dim dot to become apparent as a streak among the stars.
  4. Finding that streak. As I said, JWST is very dim, and the stars are bright. The 180 exposures were “stacked” by a program called Siril, which analyses each image, discards images in which star trailing is apparent, aligns the stars across the images, and adds the images together. In this stacked image, even very dim stars can become easily visible (almost as if a single 180-min exposure had been taken). Of course, because JWST is in a different place in each image relative to the stars, the streak created by its apparent motion consists of 180 very dim dots in a line. Fortunately my friend Barbara Bunker has lots of experience with visual astronomy (in addition to doing astrophotography) so spotting a dim streak among the stars was simple for her (I am certain that I would not have found the streak).
  5. Ensuring that the streak is in fact JWST. Many things can cause a streak in a photograph of stars. Ruling out photographic issues, objects such as asteroids, satellites, aircraft, etc. can all lead to streaks. Fortunately aircraft have characteristic lights that make them easy to recognize in a photograph. Satellites tend to move rapidly enough as they orbit to create longer streaks than a small moving object very far from Earth. To differentiate our streak (switching to plural pronouns to recognize Barbara’s contribution—my story would have ended in frustration when I failed to find the streak) we needed some indication that it was where JWST was supposed to be.

All of these challenges were overcome. That British Astronomical Association site provided enough information to allow me to point my telescope in the right place. My mount and computer controlled camera allowed the requisite number of long-exposure images to be taken. Here’s the resulting image. See the streak?

My colleague Barbara was, remarkably, able to detect the streak within seconds of seeing this photograph (I’m still amazed). Here are images with the streak pointed out, and a cropped image that might make it more apparent.

To be sure that this was indeed created by a moving object, I made an animation using all of the images (think flip-book) in which a very small, barely apparent dot can be seen moving through the length of what would become the streak in the stacked images.  It begins near the tip of the lower arrow, and is just above the tip of the upper arrow at the end of the brief video. You might have to watch it repeatedly to convince yourself that you see it.

To determine that our streak was where JWST is supposed to be required some additional data. I knew that I had pointed the scope in approximately the right direction, but did our streak line up with the path of JWST? Another amateur astrophotographer, Blake Estes, had captured a photo of the JWST on December 30, 4 days earlier. While I can’t confirm that his photo is in fact JWST, it was widely circulated online and I conclude that it is accepted as accurate.

I used Stellarium, a widely touted astronomical program, to create in image of the heavens that included the region that Estes shot, and the region that I thought I had shot. I superimposed Estes’ image on the star chart created by Stellarium by aligning his stars with those shown on the Stellarium star chart. I then did the same with my image; this was more of a challenge because there is no “up” in space and my image was not oriented the same way as the Stellarium chart. However, with some rotation and zooming of my image, I was able to align and superimpose it.

Note that this uncertainty about the orientation of the image worked to our advantage in identifying our streak as JWST without bias. Had we known the orientation of the image prior to searching for the streak, and thus known the direction that JWST would be travelling, we (i.e., Barbara) might have been biased to look only for streaks that matched this expectation. Instead, our search for the streak was “blind,” such that our expectations couldn’t bias our finding.

Next, I drew a line through the “confirmed” JWST streak on the Estes photo, and did the same with the streak in our photo. They indeed appeared to align with each other, as you would expect if they were both created by an object travelling along a smooth trajectory. When a line was extended from the Estes streak through our image, it indeed came very close to our streak. Q.E.D.

The Team (Composite photo. Barbara is in Colorado, I’m in Michigan. We’ve never met IRL.)


NOTE about equipment:

Camera: I shot my images with a cooled astrophotography camera, the ZWO AIS533 MC Pro. Digital camera sensors heat up as an exposure is taken; a long exposure can create a lot of heat, which in turn generates what is called “thermal noise” in the image—that is, the heat results in a grainy or staticy image, obscuring fine detail. Cameras designed for the long exposures typical in astrophotography have a built-in sensor cooler to combat this noise; my camera can be cooled to as low as -15° C. 

Telescope: I use an Apertura 72mm FPL-53 Doublet APO Refractor. The 72mm referes to it’s aperture, the diameter of the lens that determines its light-gathering capacity. Bigger is always better, but bigger comes at additional cost. This is a relatively small aperture for a refractor. That term, “refractor,” means that a glass lens is used to gather and focus the light, as opposed to a curved mirror (as used in a reflector telescope). Both refractors and reflectors have their advantages. Reflectors (mirror) can be made much larger than refractors (glass lens) at less cost; large reflectors are favored by astronomers who observe visually and refer to their giant scopes as “light buckets” because of their ability to collect so many photons. This can be a problem for the long exposures needed in astrophotography, as even a slight gust of wind can shake the gigantic light bucket, ruining the exposure. Reflectors also avoid the problem of chromatic aberration; different wavelengths of light are bent at slightly different angles by glass lenses, resulting in slightly different focus points for red and blue light, and apparent color fringing around bright objects.  Manufacturers of lenses can use different types of glass (the “FPL-53” refers to the glass used) and different configurations of lenses (e.g., “Doublet”) to try to overcome this aberration. Mirrors don’t suffer from this problem. However, reflectors require frequent (every observing session, some would say) adjustment or “collimation” to ensure that the optics are aligned. The smaller targe tthat they provide for the wind, and the lack of constant adjustment, make refractors the favored tyoe of telescope for astrophotographers.

Mount: I mount the telescope and camera on a Sky-Watcher HEQ5 Pro mount. This precision instrument can rotate in a manner that exactly compensates for the rotation of the Earth, allowing the view through the telescope to remain constant over time, with no star trails. Such precise compensation requires that the axis of rotation of the mount is aligned with the axis of rotation of the Earth. The first 10 minutes or so of any astrophotography outing are devoted to ensuring that this alignment is precise. If the axis of the mount points at Polaris (the North Star) it will be close, but not precise enough; Polaris actually orbits the celestial North Pole (the point directly above the Earth’s axis), about 0.7° away from it (for comparison, the full Moon has a diameter of about  0.5°) so alignment requires positioning the mount’s axis so that it is pointing to the location in the sky where the actual celestial pole is relative to Polaris. A polar clock app will show exactly where Polaris is relative to the celestial pole at any time, and is used to accomplish this.  My mount also is computer controlled, with the capacity to aim at any particular place in the heavens if it has been properly aligned with the stars. This is a convenience, but not a necessity for astrophotography.

Software: I use a program called Siril to align and stack the images. Siril automatically discards images with too much star trailing (15 of my 180 images were discarded), lines up the stars and stacks the images. The resulting stacked image will be very dark (the heavens are dim) so additional processing is needed to “stretch” the image and reveal its beauty.  Siril is capable much of this additional processing, but I almost always import the final Siril image into Raw Therapee to make my final tweaks.

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