2016 September Equinox

   On Thursday September 22nd at 14:21 UT, (9:21 am 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. 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.
   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 and U.K.

   
   
   

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.

March 2015 Equinox and Solar Eclipse

   Friday March 20th is an equinox day. This means that for those in the northern hemisphere winter is ending and spring has ‘sprung’ (starts). For our counterparts south of the equator summer is ending and fall is beginning. From a geographical perspective we would describe the Sun as being over the Earth’s equator, and as this graphic shows there would be an equal amount of daylight and night on our planet as a result.
    At mid-day on the equator the sun is directly overhead and from that latitude you have no shadow, just a ‘blob-like’ shadow at your feet as this picture of my feet taken at mid-day in Quito Ecuador shows.

    Regardless of your hemispheric preference get outside and cast a shadow!

seasons-ani  Northern hemisphere spring officially (well at least astronomically) begins at 22:45 UT (4:45 pm CST) on the 20th when the Sun reaches the celestial coordinates of 0 hours and 0 degrees as it moves northward along the ecliptic crossing the celestial equator. At this location the Sun is within the constellation of Pisces the Fishes and not just entering Aries the Ram as the pseudoscience of astrology would have you believe.

    To learn more about the celestial coordinates click here to read a previous post about seasons and the equinox.

   The time of this equinox is about 13 hours after a new Moon phase and a solar eclipse. This picture shows the shadow of the Moon cast on the Earth during a solar eclipse as seen from the International Space Station.

   Click here to see the online world sunlight map used to make the day/night graphic at the top of the page.

sun-earth   Click here to go to the NASA Sun-Earth Days web site.

   Here is a short series of hourly pictures taken during the day on the September equinox on the equator in Quito Ecuador at Collegio Menor San Francisco de Quito, a private school that I visited and did the SunShIP project with (Sun Shadow Investigation Project).

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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 Equinox

Click on graphic to see it full size.

Click on graphic to see it full size.

   On Sunday 22 September at 3:44 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.”
Click on graphic to see it full size.

Click on graphic to see it full size.

   Declination is the astronomical equivalent to latitude measuring from 0 degrees at the equator to 90 degrees at either pole. 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 most notable 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 Spring 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.

   
   
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

It’s Equinox Day!

    Today is an equinox day meaning that for us in the northern hemisphere summer is ending and fall begins, while for our counterparts south of the equator winter is ending and spring has sprung. And as the graphic shows there is an equal amount of daylight and night on our planet.
    At the equator the sun is directly overhead and from that latitude you have no shadow, just a ‘blob-like’ shadow at your feet.
    Regardless of your hemispheric preference get outside and cast a shadow!

    Click here to see an online world sunlight map.

When Day = Night

    The spring season for the Northern Hemisphere starts around March 20th.
    What does it mean when we say that a season starts? The answer to this question, in part, is based on a system of grid lines that, while similar to latitude and longitude, are not on the surface of the Earth. These lines are the celestial, or sky, grid and are literally an extension of the Earth-surface grid system into the sky. When we can extend the Earth’s equator skyward, it becomes the sky equator, dividing the sky around us into a northern and southern half. Further divisions of the sky north and south of the sky equator are known as lines of declination, whereas on Earth these are parallels of latitude. The celestial sphere is also divided into 24 sections similar to meridians of longitude. However, these lines are known as hour circles of right ascension, or hour circles. Hour circles are numbered from 0 to 23. The intersection of these hour circles and lines of declination determines a celestial object’s coordinates on the celestial sphere.
mar-equinox   For example, (using the northern hemisphere) the Sun passes through the 0-hour circle at the start of spring, and it passes through the 12-hour circle at the start of fall. Additionally the Sun’s position relative to the sky equator at this time, its declination, is 0-degrees – the Sun is ‘on’ the equator. This information, the object’s hour circle and declination, are enough to locate its position on the celestial sphere. However, an additional line can be added to the celestial sphere to show the daily changes in the Sun’s position in the sky throughout the year. This line, known as the ecliptic, represents the path the Sun seems to follow throughout a year. The Sun seems to move eastward along the ecliptic, with respect to the stars in the background, because of the Earth’s orbital motion about the Sun.
   This graphic shows a portion of the celestial sphere and grid system of hour circles and lines of declination. The Sun is located at the point where the ecliptic crosses the sky equator. At this intersection, the Sun has coordinates of 12 hours, 0 degrees. This, then, is when northern hemisphere fall starts. While these figures give its coordinate position, the Sun can also be described in terms of the constellation it is in (actually in front of), as viewed from Earth. Thus, at the start of northern hemisphere spring (March) the Sun is in Pisces the fishes, while in the fall (September), we would say the Sun is within the boundaries of Virgo.
   “Equinox” is derived from the Latin, meaning equal night, and when it occurs, the Sun rises due east and sets due west everywhere on Earth except near the poles, giving us 12 hours of daylight and 12 hours of nighttime. During the summer, the Sun rises in the northeast and sets in the northwest, and during the winter, the Sun rises in the southeast and sets in the southwest in the Northern Hemisphere.