James Web Space Telescope’s Dance

James Webb Space Telescope (JWST) was launched on Xmas Day 2021. It has now reached its final destination at the second Lagrange Point (L2), about 1.5 million km from the Earth. It will be a few months of tests and camera cooldowns before it can produce its first image, but in the meantime, though very faint, it can be spotted with amateur-class equipment.

Shining at about magnitude 17, JWST appears to be dancing in the sky due to its very particular orbit at the L2 point. Lagrange points are spots in space where there is equilibrium of gravitational force of two bodies (in this case, the Earth and the Sun). But how easy it is to spot JWST? 

First of all, one has to create an accurate ephemeris, because it is a very elusive object and can be easily confused with background stars. In a single exposure it will actually be indistinguishable from other stars, but its movement will be easily detected across exposures just a few minutes apart. The key to a successful capture is twofold: 

  1. Precise ephemeris 
  2. A mount with very high pointing accuracy

An optical tube of generous aperture can make our life easier, but much depends on local conditions, especially light pollution. A detailed tutorial explains how to obtain an accurate ephemeris from JPL’ Horizons web app. At the time of imaging, JWST appeared to be in Canis Minor, a few degrees west of Procyon towards the Milky Way in Monoceros, approximate coordinates RA 07h17m03s, Dec. +08d34'32". A plate-solving application can help ensure you are point at the right area in the sky.

For imaging, I used my ZWO ASI 071 MC Pro at the prime focus of Celestron C11. A high-end mount (10 Micron GM2000) played an important role. 

I have two images of this event. One is a composite of 14 x 3 min. exposures. The raw, uncalibrated subframes were aligned on the telescope, which keeps JWST fixed in the field of view but yields trailed stars. There is a gap in the trails, because I temporarily slewed the telescope to a brighter star for refocusing. As usual in my region, we had quite strong atmospheric turbulence. The field of view is about 10 x 6 arcmin wide.

The second exposure is actually a short movie assembled from the same subframes that were used to make the composite.

James Webb Space Telescope (JWST)


Below is the short movie:

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