June Solstice

Sun's Apparent Motion Along the Ecliptic

Sun’s Apparent Motion Along the Ecliptic – from Taurus to Gemini

   Northern hemisphere spring comes to an end and its summer begins at 5:51 am CDT (10:51 UT) on Saturday 21 June as the Sun ‘reaches’ the celestial coordinates of 23.5o north declination and 6 hours right ascension. With respect to the Earth’s surface the Sun is described as over the Tropic of Cancer, 23.5o, north latitude of the Earth’s equator. At this same time the Sun is still within the boundaries of the constellation Taurus the Bull – but just barely. Interestingly about 9 hours later, (3 pm CDT – 20 UT), the Sun ‘will move’ into the region of Gemini as it crosses the boundary between Gemini and Taurus.
   We know that it is the Earth’s orbital motion around the Sun that causes the sun’s apparent eastward motion amongst the stars in the background. This is how the Sun ‘reaches’ a celestial coordinate, how it ‘crosses’ the boundaries between constellations, or how it is ‘in‘ a constellation.
   With respect to the southern hemisphere this is the end of their summer and start of their fall season. So thinking globally my preference has been to use the name of the month to designate the season change. Hence the use of the term June Solstice rather than summer solstice.

   Follow the seasons by observing how vegetation changes during 1 year. The video below was produced by an Earth orbiting satellite operated by the NASA/NOAA Suomi National Polar Orbiting Partnership (NPP). It is a really interesting narrated tour of the Earth from orbit over a variety of geographic features and landscapes.

Just had to include this!!

Just had to include this!!

   
   
   
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.

June Solstice

Sun's Apparent Motion Along the Ecliptic

Sun’s Apparent Motion Along the Ecliptic – from Taurus to Gemini

   Northern hemisphere spring comes to an end and its summer begins at 12:04 am CDT (05:04 UT) on 21 June as the Sun ‘reaches’ the celestial coordinates of 23.5oN and 6 hours right ascension. With respect to the Earth’s surface the Sun is described as over the Tropic of Cancer, 23.5oN of the Earth’s equator. At this same time the Sun is still within the boundaries of the constellation Taurus the Bull – but just barely. Interestingly 9 hours later, (9:00 am CDT – 14 UT), the Sun ‘will move’ into the region of Gemini as it crosses the boundary between Gemini and Taurus.
   We know that it is the Earth’s orbital motion around the Sun giving rise to the sun’s apparent eastward motion amongst the stars in the background. This is how the Sun ‘reaches’ a celestial coordinate, how it ‘crosses’ the boundaries between constellations, or how it is ‘in‘ a constellation.
   With respect to the southern hemisphere this is the end of their summer and start of their fall season so thinking globally my preference has been to use the name of the month to designate the season change. Hence the use of the term June Solstice rather than the limited to northern hemisphere term summer solstice.

   Follow the seasons by observing how vegetation changes during 1 year. The video below was produced by an Earth orbiting satellite operated by the NASA/NOAA Suomi National Polar Orbiting Partnership (NPP). It is a really interesting narrated tour of the Earth from orbit over a variety of geographic features and landscapes.

Just had to include this!!

Just had to include this!!

   
   

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

It’s Aries Time

Along the Ecliptic

Along the Ecliptic

   At 5 p.m. CDT (22 UT) on the 18th, today, the sun in its apparent eastward motion along the ecliptic crosses the boundary between the constellations Pisces the Fishes and Aries the Ram as it enters the area of the sky containing the stars of Aries. This graphic shows the real position of the Sun on this date.
   The banner graphic at the top of this page shows a larger view of the area including the point, Vernal Equinox, where historically it was used to mark the starting point for the change of seasons from northern hemisphere winter to spring. This celestial position is referred to as the ‘First Point of Aries‘ even though the Sun is no longer at that position at the start of spring around March 20th. The shift of approximately one month is a result of a long term motion known as precession, or precession of the axis. precession circlePrecession is a wobble like motion the Earth has caused by the gravitational pull of the Sun and to a lesser extent, the Moon. The Earth leans at an angle of 23.5 degrees and over time, about 26,000 years the Earth wobbles and the poles of the Earth trace out a circle where any star on or near the precession circle will be the pole star.
   Another effect of precession, as the Earth wobbles, is that the celestial coordinate system, which is based on the Earth’s geographical coordinate system (latitude and longitude) moves or shifts toward the east with respect to the stars and constellations. The stars in the background stay fixed, more or less, in their location, while the celestial coordinates move as the Earth is precessing. The result is that several centuries ago the sun was in Aries at the start of spring, now the Sun is further west across Aries and has nearly precessed into Pisces.

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