By Duncan Steel 22/02/2020


Last Monday SpaceX launched another clutch of Starlink satellites into low-Earth orbit, bringing up to 300 the number of these units intended to bring 5G internet to the whole globe. In this post I present a movie showing how all 300 such satellites will be zipping around our planet over the next eight days (until the end of the month), also showing still shots for the times when this latest batch should be visible from New Zealand in the evenings of the next week or so. 

In previous posts (linked here and here) I have written about the chains of satellites observable in the evening sky an hour or so after sunset some days, or in the morning sky an hour or so prior to sunrise. That is, the satellites are in direct sunlight at their high altitude whereas the ground below is in the dark/nighttime, and so the satellites can be seen with the naked eye due to the sunlight they reflect down to us.

The absolute best way to discover when and where to look is by accessing the Heavens Above website and entering your geographical location, then clicking on the satellites for which you would like to get predictions of visibility. The International Space Station, being so large, is certainly the brightest artificial object in the sky (sometimes being brighter than all celestial objects other than the Sun and the Moon), but it is quite fascinating to see the chains of dozens of Starlink satellites now being progressively launched by SpaceX.

Having written that, I have to add that the blossoming numbers of satellites in orbit are causing headaches for astronomers. On 12th February the International Astronomical Union issued a statement describing how and why the quickly-increasing number of satellites has a deleterious effect on astronomical observations.

This past Monday, 17th February, the latest launch of sixty Starlink satellites occurred. At the time of writing (or, more precisely, me making the relevant calculations) this cluster of satellites was still in one piece, the individual satellites not yet having been released so as to result in a chain. This one module has been given the NORAD catalogue number 45242.

What I have done here is to insert into STK (from Analytical Graphics, Inc.) the best-available orbits of all the Starlink satellites, the operational satellites numbering 237, plus the Starlink-4 (NORAD 45242) module. The individual satellites I have shown below as yellow dots; the Starlink-4 module I have shown as a violet dot, also indicating its orbit about the Earth with an elliptical line.

As I write late on Friday the 21st, I note that the Starlink-4 module should be visible from NZ at about 05:20 in the morning (of Saturday the 22nd). To see the geometry, watch the movie I have linked here. That movie shows the movements of all these satellites between the start of today (21st February) through to the end of the month (the end of 29th February/the start of 1st March). Note the movie is 432 seconds long, and occupies 260 MB.

(In passing I note that the instant in question – the end of February and the start of March – is when the ‘leaping’ occurs in a leap year; that is, the Dominical Letter used in calculating Easter is adjusted by one.) 

Over the next seven days there will be opportunities to see Starlink-4, presumably with the individual satellites being released so as to form a chain, each evening at times around 9pm. Most of NZ should get the chance to witness the passing of this, and other satellite chains.

The times at which the visibility will start are approximately as follows:

Saturday 22nd: 21:24

Sunday 23rd: 21:20

Monday 24th: 21:16

Tuesday 25th: 21:09

Wednesday 26th: 21:00

Thursday 27th: 20:50

Friday 28th: 20:33

The geometries for these seven passes are shown in the header to this blog post (for 22nd February) and then in the six frame-grabs below.

In these graphics I have shown lines connecting Wellington and Auckland with the satellite (Starlink-4) at the time the pass begins (i.e. the pass which will be visible from NZ, clouds allowing).

I emphasize that the times I have highlighted here are only those at which the Starlink-4 module is making an overpass near New Zealand, and is illuminated by sunlight whereas the land below is in darkness, making it feasible to see the satellite with the naked eye as a bright pinprick of light passing across the sky at a rate such that it takes several minutes to travel from horizon to horizon. (Actually, satellites in such low orbits are zipping along at about 8 kilometres per second/28,800 kph.) There are many other satellites in orbit that are easily spotted, and in particular if you watch the movie you will see chains passing close to overhead wherever you are, the ticking time display indicating to you when you should be outside and watching the sky. What you need to look for in the movie – which is about 432 seconds long – is the time when the satellite chains seem to be about 10-20 degrees inside the shadowed region of the planet, with your location also in the dark (i.e. it is nighttime, but the satellite at its altitude is still bathed by sunlight).

For more-definitive assessments of satellite visibility, with specified look directions and anticipated brightnesses, again I urge you to make use of the the Heavens Above website.