September 2014 Equinox Sun Is Not In Libra

Click on graphic to see it full size.

Click on graphic to see it full size.

   On Tuesday September 23rd at 2:29 UT, (Monday September 22nd at 9:29 pm CDT) the Sun will have reached the astronomical coordinates of 0 degrees declination and 12 hours of right ascension, or RA. This places the Sun within the boundaries of the constellation Virgo the Maiden, or as some would say, “the Sun is in Virgo.” This is the actual position of the Astronomical Sun as opposed to the pseudoscience of astrology which has the astrological Sun entering the constellation of Libra the Scales.
   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   Declination is the astronomical equivalent to latitude measuring from 0 degrees at the equator to 90 degrees at either pole.
Click on graphic to see it full size.

Click on graphic to see it full size.

Right ascension, or RA, is like longitude except that there is only east RA. The globe is divided into 24 sections, and like meridians of longitude, these hour circles are 15 degrees wide at the celestial equator and taper to a ‘point’ at the north and south pole respectively. In RA the ‘hour’ circles are counted from 0 hours to 23 hours. The 0 hour circle is at the intersection of the ecliptic and the celestial equator in the constellation of Pisces the Fishes.
Click on picture to see it full size.

Click on picture to see it full size.

   In a class lesson about seasons today would be one of the two days during the year when the Sun would be described as being over the Earth’s equator. If you were at the Earth’s equator the Sun would have an altitude of 90 degrees, or straight up in your sky at your local time for midday. At that moment there would not be a shadow. However at any other latitude, north or south at midday, the Sun would be at an angle less than 90 degrees and there would be a midday shadow. (Midday is the local time when the Sun is halfway between local rising time and local setting time. At any midday the Sun is at its maximum altitude above the southern horizon in the northern hemisphere, or is at its maximum altitude above the northern horizon in the southern hemisphere.)
   What is often noted about an equinox day is the reminder that equinox means equal night as a reference to there being equal amounts of daylight, and night. Also on an equinox day the Sun would rise due east and set due west for virtually everywhere on the globe. The times for sunrise and sunset would be approximately 12 hours apart, and the rising time would be around 6 am local time, and the setting time would be around 6 pm local time.

Hola Moon doh

Hola ‘Moo’ndo! Think Globally.

   So why “September Equinox” instead of using the more familiar “Fall Equinox”. Primarily because the southern hemisphere is also changing seasons on this day however for the southern hemisphere this is the start of their spring season. Despite the opposite seasons it is somewhat of a northern hemisphere bias that traditionally we would call this day the “Autumnal or Fall Equinox”, and in March we would say the “Spring” or “Vernal Equinox”. I favor the use of the name of the month so that regardless of which hemisphere it is just simply the March equinox or the September equinox, and by extension we would also have the June solstice and the December solstice..
   
   This short video shows students at Colegio Menor San Francisco de Quito, a school in Quito Ecuador, measuring the altitude of the sun hourly on the day of the 2004 September Equinox. They were taking part in Project SunShIP, Sun Shadow Investigation Project. There are also some pictures showing a local midday shadow from other participating schools in the United states.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Mercury and Spica

20sep-ecliptic   Saturday evening the innermost planet Mercury will come within about 0.5o of the star Spica, a bluish-white star in the constellation Virgo the Harvest Maiden. While the pair is around 25o east from the setting sun the angle of the ecliptic is low compared to other days of the year.

Click on graphic to see it full size.

Click on graphic to see it full size.

   Viewing these two may definitely be a challenge because of how low they will be when the sky darkens enough to see them. However using binoculars or a wide field view eyepiece in a telescope they can be seen. And the contrast in apparent magnitudes is easily noticed (assuming you can see the pair). Mercury has an apparent magnitude of 0.11, while Spica has an apparent magnitude of 1.0.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

September Apogee Moon Near Jupiter

20sep-apogee_moon    Our Moon orbits around the Sun with the Earth and from our perspective on the Earth the Moon appears to circle around the Earth. However in reality the Moon orbits the Sun together with the Earth*.

Click on graphic to see it full size.

Click on graphic to see it full size.

   This very thin 28.2-day old waning crescent Moon shows only about 11% of its disk and rises before sunrise local time. Given its thin crescent shape it may not be noticed. However the thin Moon will be in conjunction with the planet Jupiter, coming within a few degrees from Jupiter. And the two should make a striking pair. This waning crescent Moon reaches apogee this month on Saturday September 20th at 9 am CDT (14 UT). At that time the Moon will more or less be at a distance of 31.85 Earth diameters (405,845 km or 252,180 miles) from the Earth.

   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Sun Enters Virgo

view_from_earth   Wednesday September 17th at 1 UT (Tuesday September 16th at 8 pm CDT) the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Leo the Lion and into the constellation of Virgo the Harvest Maiden. This is the true or actual position of the Sun as opposed to the pseudoscience of astrology which usually has the astrological Sun one constellation ahead or east from the Astronomical Sun’s position.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

The Rocking Moon

   On Monday September 15th the Moon will show its maximum libration. Lunar libration is a tilting motion of the Moon as it revolves around the Sun with the Earth. In a way like how the Earth’s axial tilt gives rise to seasons as the Earth “leans toward the Sun in northern hemisphere summer, and then is tilted away from the Sun for northern hemisphere winter”. From the Sun this would look like the Earth is nodding back and forth – tilting towards and then away from the Sun.
   Our Moon has an orbit that is tilted about 6o away from the Earth’s orbit, and the Moon has an axial tilt of about 1.5o. So the Moon will also have this apparent motion of tilting back and forth and from side to side every day, as well as every lunar cycle.
   There are three ways to look at libration (seriously – three ways to look). However all three combine to give a nausea inducing motion if sped up!
   Lunar phases have been ‘turned off’ for this simulation.

   Lunar phases are shown for this simulation.

   Libration in Latitude has the Moon nodding forward and backward allowing one to actually see more than 50% of the Moon. During this libration more of either the Moon’s north or south pole is more visible – up to 59%. Libration in longitude is an effect caused by the elliptically shaped lunar orbit. This causes the Moon to oscillate back and forth appearing larger or smaller. The third type of libration is Daily or Diurnal Libration. This is a left to right type of motion caused from the different viewing perspectives between when the Moon rises and when it sets. The setting Moon is approximately 4,000 miles (6,437 km) further from an observer then at moonrise. This difference is enough to give the Moon a left to right oscillation.

Click on graphic to see it full size.

Click on graphic to see it full size.

   The waxing gibbous Moon rises around midnight local time and is above the southern horizon at sunrise.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Moon The Sisters

Click on graphic to see it full size.

Click on graphic to see it full size.

   Sunday morning, September 14th, before the Sun rises look toward the eastern horizon for the waning gibbous Moon to be rising in between two open star clusters, the Pleiades and the Hyades. Both of which are part the constellation of Taurus the Bull. As the banner graphic at the top of the page shows the moon is approximately 7o from either open star cluster.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

September Moon At Descending Node

11sepmoon-descending_node   Thursday 11 September at 7:35 UT (2:35 am CDT) our Moon will be crossing the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.

Note the ecliptic is the line with ‘Apr’ however that is a reference to when the Sun will be at that point along the ecliptic and not the date for this node crossing.

Click on graphic to see it full size.

Click on graphic to see it full size.

   Look for the just past full Moon, the waning gibbous Moon above the southwestern horizon in the pre-dawn skies. It will be visible for most of the morning until the sky brightens and moon-set at around 11 am local time.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.