Earth at its 2015 Perihelion

Earth at Perihelion   Feel the Heat?
   Sunday January 4th at 7 UT (1 am CST), as the Earth continues its annual trek around the Sun, the Earth reaches a point in its orbit that is called perihelion. Perihelion is the minimum distance that separates the Earth from the Sun, and we are the closest to the Sun for the year at this point in the orbit. So, at 12:00 UT (0600 CST) the Earth is 0.98328 AU (91,401,586 miles; 147,096,594 km) from the Sun. Approximately one-half year or one-half revolution later, on 6 July, the Earth is at aphelion and is 1.01668 AU(94,506,310 miles; 152,093,163 km), its maximum distance from the Sun for 2015. This difference in distances is due to the shape of the Earth’s orbit being elliptical rather than circular. However the Earth has a mildly elliptically shaped orbit that is closer to being slightly out-of-round than the incorrect, very elliptical orbit that is often shown – like the illustration used here.

sun2014-ani   In Astronomy the shape of a planet’s orbit is called eccentricity, with 0 being a circle and 1 a straight line. Any value between 0 and 1 represents an ellipse. The shape of the Earth’s orbit is so close to being circular that the apparent size of the Sun does not appear to change as this animated graphic shows. The difference between perihelion and aphelion is about 3%.

   Eccentricity for each planet is listed below for comparison.

Planet	   Eccentricity	
Mercury	   0.2056
Venus	   0.0068
Earth	   0.0167
Mars	   0.0934
Jupiter	   0.0484
Saturn	   0.0542
Uranus	   0.0472
Neptune	   0.0086
Pluto	   0.2488

   To read more about the Earth’s orbit and get some teaching ideas click here to download a PDF copy of my January 2011 Scope on the Skies column Solar Explorations.
   Here is a good classroom activity about the Earth’s orbit and its effect on the apparent size of the Sun: Why Does the Size of the Sun Appear to Change? A Year of the Sun.
   
   
   
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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.

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.

Climate Change? — Yes!

mb   Recently on Facebook I got into an interesting yet sort of depressing back and forth discussion about climate change with a young man. This was started after I had posted some comments based on Senator Marco Rubio’s denial of the science about climate change during an interview he had about a week ago. In defense of not accepting the climate change science my Facebook challenger’s offer of ‘evidence’ against climate change looked more like the talking points one hears on the news or news channels. Unfortunately many of our elected officials on local and national levels, regardless of their political affiliation, do not accept the science of climate change.

   So when I came across this video I had to share it!

   Click here to go to the Climate Name Change web site.

    Click here to go the Think Progress web page with for the following article, 99 One Liners Rebutting Denier Talking Points with links to the full Climate Science

To quote Albert Einstein:
“Sometimes I wonder whether the world is being run by smart people who are putting us on, or by imbeciles who really mean it.”

   
   
   
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 the Time of the Season

A Martian Year

A Martian Year – at One Earth Month Intervals

   Today is the northern hemisphere spring equinox on the planet Mars as the planet transitions from winter to spring during its 684 Earth day orbit around the Sun. Seasons on Mars are marked by the planet’s heliocentric longitude coordinates using the position of Mars along its orbit around the Sun. Each seasonal start/ending point is 90 degrees apart, but because of its elliptical-shaped orbit each Martian season is of varying lengths. At the Martian spring equinox Mars is at 0 degrees longitude.
   I’m not exactly sure why this particular date is used but by international agreement astronomers have selected 11 April, 1955 as 0 degrees for year 1 of this Martian calendar. What this means is that today, 31 July Earth time, is the start of a ‘new year’, the first day of spring for year 32 using the aforementioned calendar system.

Year 32
0 degrees — Spring Equinox — Jul 31 2013
90 degrees — Summer solstice — Feb 15 2014
180 degrees — Fall Equinox — Aug 17 2014
270 degrees — Winter Solstice — Jan 11 2015
Year 33
0 degrees — Spring Equinox — Jun 18 2015

Learn a little (or a lot) more about Mars at the NASA/JPL Mars Curiosity mission web site.

Here is approximately 3 minutes worth of Mars from the Orbit performance.

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

Arizona Pans

   For the past week or so I have been in Tucson Arizona visiting family. One of the benefits of this part of the country is that the skies are clear — most of the time. With every visit here I make plans for taking some pictures at night as well as during the day. This visit was during the local monsoon season when the skies are cloudy, the temperature is high, as is the humidity, and it rains. So most of my pictures are of the spectacular desert and mountain scenery around the Tucson valley and mountains.
   Using the Microsoft software program, Photosynth, I’ve composed several panoramas of various locations around the Tucson area. Panoramas are from a park and a natural spring on the east side of Tucson; the Saguaro (Cactus) National Park; and along the Catalina Highway on Mt. Lemmon.
   Click on the link below each picture to go to my Photosynth web page to see that panorama.








rr

Saguaro National ParkRincon Mountain Valley


rm

Saguaro National ParkRincon Mountains


jj

Saguaro National ParkJavelina Point

   

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

Super Mini-Sun

Sunrise - 5 July

Sunrise – 5 July

   This Friday, 5 July, the Sun will be its smallest appearing and most distant for the year as the Earth reaches aphelion, the point in its orbit around the Sun where the Earth is at its maximum distance from the Sun. At 10 am CDT the Earth and Sun will be separated by 94,508,19 miles, (152,096,155 km). Conversely the Earth and Sun will be at their closest next year, perihelion, on 4 January 2014 when the two will be separated by 91, 405, 333 miles (147,103,000 km).
   The difference between the two distances is approximately 3 percent and is as a result of the Earth having a slightly elliptical shaped orbit. With a nearly circular orbit this in turn helps to explain that it is not distance from the Sun that is a reason for seasons. Seasons on Earth result from the Earth’s 23.5 degree tilt on its axis and its revolution around the Sun.
   Important note: the banner graphic at the top of the page is not actual size!

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