Saturday, December 3, 2022
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Night Sky NewsNight Sky - September 2015 Observations - Northern and Southern Horizons

Night Sky – September 2015 Observations – Northern and Southern Horizons

Looking North in Autumn – Big Dipper low in the Sky

Cycling home in the early evening, I enjoyed watching the wisps of interstellar clouds (of stars and stardust) rise up overhead into the northern reaches of the constellation Cygnus.  It is truly a joy to be able to see the Milky Way in Mississippi Mills. I also noticed the prominently low position of the bowl of the Big Dipper, and many people are often surprised by the change in orientation of the Big Dipper over the course of the year. It is, in fact, the ‘course’ of the year, or shall we say the earth in its ‘course’ that allows us to see our orbital direction change by viewing the circumpolar constellation change ‘in due season’. Unlike other constellations like Orion, that  are visible only in Winter , or Sagittarius that appears only in Summer during the observable part of the evening, say, 10pm to midnight, the Big Dipper (Ursa Major) can be seen after sunset every clear night. It is never hidden by the glare of the Sun because it is located  close  enough to the pole of the Earth’s axis, i.e.  far enough north of the celestial equator . This means  that its stars are above our horizon after sunset even at their lowest (below the pole star). You can see  the 7 stars  in the evening every clear night of the year at our latitude of 45 degrees. As you can see in the annotated drawing of the Beginners Observers Handbook, the Autumn position of the Big Dipper points to Polaris from below the ‘pole’. For an animation of this concept see Ursa Major- the Big Dipper and Polaris

Four Seasons show the circumpolar rotation of the Big Dipper
Four Seasons show the circumpolar rotation of the Big Dipper


The little timekeeper pendant that you see superimposed on the diagram can be used to match the position of the Big Dipper to the image. On the back of the pendant, the pointer lies over the approximate date (late September) and the time of night (say, 9pm) when the Big Dipper of the pendant matches the orientation of the Big Dipper in the Sky. When that pointer is vertical, you can read off the approximate time of night when you observe the Big Dipper in that orientation.

Looking South  on Sept 27 2015 , we will experience a Full  moon at perigee (hence it appears about 15 % larger than at apogee) go into eclipse of the Earth’s shadow.

Properties of this eclipse as described in the media:


  • “Blood” moon – actually more like “ruddy” colour:  This total eclipse will show the full moon in ruddy orange due to the scattering of light in Earth’s atmosphere: The Moon does not completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth’s atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse.The red coloring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth’s atmosphere, where it is scattered (see the Millstone article October 8 2014 – Rain on Lunar Eclipse)


  •  “Supermoon”  The term ‘supermoon’ describes when the  moon reaches its full phase at or near its closest approach to Earth, and appears abnormally large and bright as a result.  It is about 14 % larger diameter in the sky with at 30% greater surface area to be illuminated by the Sun at Full Moon. The Sept. 27 lunar eclipse is quite special; the last ‘supermoon’ eclipse occurred in 1982, and the next won’t take place until 2033.

If the sky is reasonably clear, this lunar eclipse will be visible as the earth’s shadow passes over the moon as shown at these times for our location:

septEclipse2015Unlike the April 4 2015 lunar eclipse that was not observable from our location, the moon had already set! (see Morning Moonset Eclipse -April-4-2015) this one will be visible (assuming clear skies), as the moon will be above the Southern Horizon as shown in the Stellarium image below.

Looking South-East – evening of the Lunar Eclipse (Sept 27 2015)




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