Mornings Have Hang Ups!

   Northern Hemisphere winter in addition to chilly or cold mornings may sort of warm you, at least in your mind. If you are outside looking at the sky, over the eastern horizon is a large triangular shape of three bright stars. One star each from three different constellations. Deneb in Cygnus the Swan, Vega in Lyra the Harp, and Altair in Aquila the Eagle. This is the asterism (star pattern but not a constellation) the Summer Triangle. There, warmer now?!
   So if you are outside checking out the Summer Triangle, or perhaps Mars and nearby Antares and you have an optical aid like binoculars or a lower power wide-field eyepiece in your telescope aim them and your eyes toward the star Altair. In dark enough skies you can make out the stars making up Sagitta the Arrow a few degrees away from Altair.
   As Altair is rising and with binoculars move the field of view up to the left until the stars of Sagitta fill the field of view. This small constellation, yes a constellation, could be used as a sort of pointer stars to look a few degrees away for a small open star cluster, Brocchi’s Cluster, or more commonly known as the ‘Coathanger Cluster’.
   So if mornings with stars like this don’t warm you up then wait a few months of Earth revolution and these same stars will be showing up in the warmer evening skies of Northern Hemisphere summer and fall.

   
   
   

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Earth at Perihelion – 2020

   Feel the Heat?
   Sunday January 5th at 8 UT (3 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 this year, 2020, the Earth is 0.9832 AU (91,398,199 miles : 147,091,144 km) from the Sun.

   Approximately one-half year or one-half revolution later, on July 4th, the Earth is at aphelion and is 1.01669 AU (94,507,634 miles; 152,096,155 km), its maximum distance from the Sun for 2020. This approximately 3% difference in distances between perihelion and aphelion 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.


Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


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Mid-Winter Skies

   Tuesday evening December 24th around sunset or after the skies darken look toward the western horizon and you can’t miss noticing the bright celestial object – the inner planet Venus. Also, despite the fact that we are now two seasons away from our summer (Northern Hemisphere), over the western horizon are three stars making up the ‘Summer Triangle’. These three stars each belong to a seperate constellation but together they form an asterism,not a constellation, but a recognizable star shape.

   Wednesday morning December 25th look toward the eastern horizon for the ‘Red Planet’ (Mars) to be above the horizon and about 15o from the reddish star Antares in Scorpius the Scorpion. In this graphic Antares is just above the horizon.
Higher above Mars, toward the right or the west, is a the bluish star Spica in Virgo the Harvest Maiden. And higher still but toward the left is another reddish star. This is Arcturus in Bootes the Herdsman.

   As this year and decade come to a close I’d like to thank all my readers and the universe in general for allowing me an opportunity to share things celestial.
Have a happy and safe Holiday however you celebrate.


Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


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Sun Does Enter Sagittarius

16dec-view-from-earth   Wednesday December 18th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Ophiuchus the Healer and into the constellation of Sagittarius the Archer. 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. Ophiuchus the Healer is the 13th Astronomical Zodiac constellation based on the location of the ecliptic and the Sun’s actual position relative to the stars and constellations in the background.

   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.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


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2019 Martian Summer Solstice

A Martian Year

A Martian Year – at One Earth Month Intervals

   Tuesday October 8th marks the summer solstice on the planet Mars as Mars transitions from spring to summer 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.

   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 on Tuesday October 8th, Earth time, it is the start of summer during year 35 using the aforementioned calendar system.

Year 35
0 degrees — Spring Equinox — March 23 2019
90 degrees — Summer solstice — October 08 2019
180 degrees — Fall Equinox — April 08 2020
270 degrees — Winter Solstice — September 02 2020

Year 36
0 degrees — Spring Equinox — February 07 2021
90 degrees — Summer solstice — August 25 2021
180 degrees — Fall Equinox — February 24 2022
270 degrees — Winter Solstice — July 21 2022

Learn a little (or a lot) more about the exploration of Mars at the NASA Journey to Mars web site.

   
   
   

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September Equinox – 2019

   On Monday September 23rd at 7:51 UT, ( 2:51 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.

   
   
   

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Sun Does Enter Virgo – 2019

view_from_earth   Tuesday September 17th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation of 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.
   In a couple of days the Sun, according to astrology, will cross the ecliptic moving southward crossing from Virgo into the constellation of Libra the Scales. We know this day as the September equinox, which this year is on the 23rd.

   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.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


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