Well, the early Wednesday morning observing session for the Starlink satellites string of pearls was clouded out and rained out. But we have found some more early morning viewing times hopefully with clearer skies.
So, how do we go about finding when the Starlink satellites will be visible overhead? There are probably many possible sources, but we go regularly to websites such as heavens-above.com and celestrak.com. These sites allow the observer to enter his location and then determine the next possible transit times for that location. Check out the Celestrak animation below which shows the orbital path of both of the Starlink 60 satellite constellations. One group appears to have already been dispersed along the orbital path and we are still apparently lucky to perhaps view the 2nd group of 60 satellites while they are still aligned in a long pattern called a string of pearls.
|Celestrak offers really great animations of satellite orbits and transits (Source: www.celestrak.com)|
The heavens-above website shows upcoming transits for your location and some rough altitude and azimuth pointing angles as well as brightness estimates. I used these estimates for the first DSLR image capture of the string of pearls as described in previous post of November 13. (You can check that post out at: http://www.palmiaobservatory.com/2019/11/hooray-followup-on-what-next-transit-of.html)
The screenshot below shows the latest predicted transit times used for this morning's clouded out observing session. It is interesting that not only are the satellites tracked and displayed but also the second stage of the Falcon 9 rocket. It is not clear how long the rocket remains in orbit.
|Header definitions for some Starlink transits visible from Orange County location (Source: www.heavens-above.com)|
For future potential viewing sessions, we can identify several early morning sessions for November 21-23. There could be other opportunities but the longer we forgo looking for the satellites the higher the chances that they will be dispersed to the assigned orbital positions and won't be visible anymore as a long string of pearls. The satellites are apparently painted black to help reduce light pollution, but sunlight reflecting from the solar panels should still be visible.
Anyway, a portion of the potential observing opportunities on Thursday and Friday, November 21 and 22, is shown below.
Also another portion of the predicted transit table is shown below for Saturday, November 23. Remember the listed times are 24-hour clock times for PST that is early in the morning.
|Some Starlink transits visible from Orange County location for Nov/23 (Source: www.heavens-above.com)|
Luckily we can refer to available websites such as Heavens-Above and Celestrak to provide viewing angles and transit times for these satellites. If we had to calculate the pointing angles ourselves that would be a lot of work.
Let's pause for a little technical discussion about how satellite orbits are described, which is the Two Line Elements (TLE's), that NORAD assigns to all objects orbiting around the Earth. This format allows anyone to calculate the future location of a satellite. My introduction to TLE's was during the SpaceX Falcon Heavy launch from Kennedy Space Center last as described in the blog post of February 8, 2018. You can check out the details of a great Orbital calculation textbook ("Orbital Mechanics for Engineering Students" by Howard Curtis), with which you can do your own orbital predictions and if that is not your thing there are some photos of the launch at: http://www.palmiaobservatory.com/2019/11/hooray-followup-on-what-next-transit-of.html
Several of us OCA members traveled to Florida to watch the launch of the first Falcon Heavy rocket, which had a payload of Elon Musk's Red Tesla. We knew the TLE for the Red Tesla, which was visible with small telescopes for a few days after launch and I wanted to try finding it, but couldn't figure out where to point my telescope. So, now, you can easily go to Celestrak website and get the TLE's for any satellite, not just the Starlink constellation of satellites shown here below.
|Portion of the table of Starlink Two Line Elements (TLE's) (Source: www.celestrak.com)|
The TLE's contain enough of the Keplerian elements needed to calculate where the satellite will be at any future time and the sky location at which it will be located. The TLE's are generated by NORAD, which has the responsibility to keep track of all of the satellites and other space junk in orbit. The definition of the two lines of the TLE's are defined below in screenshots of the Wikipedia page.
|Definition and format of values in Line 1 of the Two Line Element (Source: Wikipedia)|
Until next time (keep looking up to the sky; who knows what you will find?),
Resident Astronomer George
If you are interested in things astronomical or in astrophysics and cosmology
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