Oct 2017

Not one, but TWO ISS lunar transits in mid-Nov.

by John Hlynialuk
Lately I have taken to observing ISS transits of the Sun and Moon. These occur much more often than solar transits of planets (which are only possible for Mercury and Venus, both of which I have seen). Of course, no planets can pass in front of the Moon (unless we get a stray asteroid or other object in transit) but the International Space Station does this on a regular basis.

So far I have spotted one lunar and one solar ISS transit (Oct 4 and Oct 9) and have reported on the former event in the
SGN issue for Nov 2017 (pg 5). Click to download a copy.

The website I use to determine the best viewing locations for ISS transits is
www.transit-finder.com. It allows you to designate your home location latitude and longitude and select a travel radius and range of dates (about a month ahead). I picked 140 km as a travel radius, and it gave me 8 transits from Oct 30 to Nov 22, including the two described below.

The morning sky is the place for planet groups right now and will be until the end of 2017. Venus, Jupiter and Mars are located along the ecliptic over a span of about 30° and they are joined by the last crescent Moon in mid-Nov and mid-Dec. Check
COMING EVENTS and SKY SIGHTS on this website for details about some of the more interesting events.

The planets and Moon in the eastern sky before dawn are the backdrop for two interesting lunar transits by ISS that happen on the mornings of Nov 14 and Nov 15. The ISS (with a crew of 6 aboard) will be visible each morning crossing the sky from west to east. On Nov 14, around 5:56 am EST, look northwest and halfway up to the zenith. ISS will be bright that morning reaching -3.8 magnitude, -as bright as Venus! The heavens-above star map for the track of ISS is below:

Nov 14 ISS pass star map

ISS will appear as a very bright moving point of light crossing the sky from NW to SE and towards the crescent Moon above the south-eastern horizon. For most of us in Grey and Bruce, it will just miss the Moon, but if you are on the Cabot Head Rd about 4 km south of the lighthouse, you will see it pass right across the lunar crescent! (See the inset box on map below). The ground track of the ISS shadow is like an eclipse shadow with a specific width and path and is show shaded in blue on the Google map below. The only place it crosses land close to us on Nov 14 is across Cabot Head on the Bruce. The rest of the track is over Georgian Bay although it reaches land again in the Wyevale area and Horseshoe Valley. The location of the only observing spot for Bruce-Grey is shown below:

Nov 14 lunar 558pass


The pass of the ISS downwards across the crescent Moon will take about only 1.8 seconds and it will be illuminated so you will be able to follow it as it approaches the Moon quite easily.

A repeat of this happens again the next morning on Nov 15 at 5:08 am EST. This time a wider audience can get a view, and anyone from Miller Lake to Cape Croker will see it even though the lead up will be much shorter. This time ISS comes out of shadow just before it encounters the Moon, so look at the crescent at the appropriate time and the space station will appear right above it and slowly drop down to cross the Moon’s thin face. Those of you living in Lion’s Head can see it from home if you have a low enough eastern horizon where the Moon can be seen above the trees. (I suggest the Isthmus Bay Road which is where I will be set up if the weather allows).

Nov 15 ISS pass star map


Nov 15 wider view


The two maps from transit-finder.com show the entire track across the Bruce (above) and a close up of the the track across Lion’s Head (below). Isthmus Bay Rd about 2 to 3 km from “city centre” is a good location to view since it has a nice clear horizon to the east where the crescent Moon will be rising. This pass lasts about 4.5 seconds which is close to the maximum that can occur. Lots of time to get a good look at the ISS! I suggest you fill the FoV of your scope with Moon and watch the action! And if you get some images please let us all have a look by posting them here. I guarantee HOME page coverage.

Nov 15 lunar pas 508