Planning a Solar Eclipse Expedition

There will be a total eclipse of the Sun on August, 21, 2017 beginning in Oregon with the Moon’s shadow racing across a thin swath of the United States and ending in South Carolina.  The path of totality will not cross Maryland, so an expedition is required to go see it. I have a telescope, a camera, a Jeep, and a sense of adventure. Why wouldn’t I mount an expedition to see one of the most awe-inspiring astronomical events that humans have ever witnessed? Please check back to this post as I periodically update with specifics as my planning exercise progresses.

March 1, 2015: I begin planning with a few parameters in mind: 1) view the eclipse at the point of the longest period of totality, 2) temper that with finding a point where the weather most likely to be clear, and 3) find a jumping off point where I can quickly shift east or west to avoid cloudy skies.  Of course, driving to Oregon is out of the question, so perhaps any point from say Missouri to South Carolina might be a reasonable target.

March 5, 2015: It is a snowy day in Maryland, which somehow seems an appropriate time to begin working in earnest on an expedition plan for a solar eclipse that will occur on a hot August afternoon almost two and a half years hence. I discovered a great information source: www.eclipse2017.org, and I recommend this Web site for anyone wanting to learn more about this eclipse, or stay current or related developments. Among the things that I learned that makes an expedition an imperative is that my location in Maryland will experience about 85% totality. This will never do!

The the ideal place to view the eclipse is at the longest point of totality (2m44s), which will be in Shawnee National Forest in southern Illinois. Coincidentally, the path of totality within a five-hour drive east or west of this point is in a zone that historically experiences 30% to 40% cloud cover in mid-August. This is much better odds than I can ever get in Maryland.

The initial plan that I have formulated is arrive in Louisville, KY the afternoon before the eclipse. This is a 9-hour/600 mile drive from Maryland, and Shawnee can be reached in another three hours the next morning. Also from Louisville, there are good routes for moving east or west along the path of totality to reach alternate viewing cites if Shawnee is predicted to be clouded over.

March 7, 2015: Looking at east-west options that are reasonably accessible from Louisville, I have selected St Louis, Missouri (4 hours, 250 miles) to the west, and Franklin, Tennessee (5 hours, 380 miles ) to the east the boundaries for selecting alternative viewing sites. I am fairly happy, at least for the moment, to have framed a coincidence of maximum totality, good weather, and accessibility from where I live. Before examining specific viewing sites, I will next work on a viewing plan that can be modified to account for any location that I may elect for viewing the eclipse.

 February 24, 2016: It has been almost a year since I added planning details, but that doesn’t mean that I have not given a considerable amount of thought to the matter. As I add this entry, it is a cold, blustery, and snowy winter’s day in Saint Louis, just over a two-hour drive to the point of the eclipse’s longest duration, just south of Carbondale, IL. I have formulated Eclipse Logistics Plans A and B. Plan A is a drive straight to Carbondale on the day before the eclipse if Carbondale’s weather is promising. I would either view the eclipse from the Southern Illinois University (SIU) campus where the duration is only four seconds less than the eclipse duration at the longest duration point, or drive the six to eight miles required to get exactly on the eclipse center line. Plan B, if Carbondale’s weather outlook is not so promising is to drive to Louisville, KY the day before the eclipse and bed down there. This would require that I wake up at zero-dark-thirty the next morning, assess the best weather prospects either east or west of Carbondale, and drive there leaving sufficient time to set up before the eclipse begins. In the next installment, I will capture my thinking on what equipment to take and how to observe and/or photograph the event.

 

March 2015

INTRODUCTION

Eastern Daylight-Saving Time (EDT) starts on March 8th, and March 20th is the first day of astronomical spring, or the vernal equinox. Although not perfect, the weather becomes a lot more tolerable this month, and the days are getting longer at a rapid pace. Getting dark later seems to be an equitable trade for the better weather after February’s extreme cold temperatures.

About Scope Out      How to begin Observing the Night Sky

THE CONSTELLATIONS

The sky map below represents the sky as it will appear in mid-March at the end of astronomical twilight,  the arrival of complete darkness, at 7:45pm EDT. The Scope Out monthly focus is on the constellations that are  just to either side of the meridian, which is near the 6th hour (6h) of right ascension line in the March sky map. For a primer on how to use this sky map, please read How to begin Observing the Night Sky.

Scope Out divides the celestial sphere into three zones to aid in finding constellations:

1. Circumpolar Constellations:  Find Camelopardalis, Lynx, and Ursa Major in the northern sky above Polaris.

2. Northern Constellations:  Orion still catches the eye, but it is beginning to march off of the stage on the western horizon. Find March’s remaining northern constellations, Cancer, Leo, and Leo Minor near the zenith.

3. Southern Constellations: The best-placed constellations in March are Hydra, Sextans, Pyxis, and Crater. Some of these constellations, Pyxis, Hydra, and Crater in particular, are difficult to view because their extreme southern placement prevents them from rising very far above the horizon.

April
The April Sky at Nightfall. Jim Johnson. December 2014.

 

THE PLANETS

planets
Colors of the planets. This picture is not to scale. Image from NASA’s Planetary Photogrounal at http://photojournal.jpl.nasa.gov/

Mercury remains hidden all month as it makes its pass around the far side of the Sun. Venus and Mars continue share the western horizon, and can be seen about an hour after sunset. While Mars grows dimmer and is placed a little closer to the sun each evening, Venus’ brightness will dominate the western sky after sunset, and will appear a little higher above the horizon each evening.  Jupiter is just past opposition, and is already well above the eastern horizon after sunset. Saturn continues to rise earlier each evening, appearing above the eastern horizon about four hours after sunset. Uranus is on the western horizon near Venus and Mars all month, and can be glimpsed with optical aid about an hour after sunset. Neptune is too near the sun to be seen this month.

THE LUNAR CALENDAR

March 2
Conjunction with Jupiter
moon_phases_small_full March 5
Full Moon
March 12
Conjunction with Saturn
moon_phases_small_lastqtr March 13
Last Quarter
moon_phases_small_new March 20
New Moon
March  21
Conjunction with Mars
March  22
Conjunction with Venus
moon_phases_small_firstqtr March 27
First Quarter

EVENTS

Vernal Equinox – March 20, 2015 at 22:45 UTC (18:45 EDT).

The Sun’s arrival at the zero hour of right ascension marks the vernal equinox, or beginning of astronomical spring. This is the point at which the ecliptic intersects the equator. which is why on this day the days and nights are of almost equal length. Read The Ecliptic – A Trace of the Sun’s Path across the Celestial Sphere for more information on the Sun’s movements on the ecliptic.

Conjunction of Venus and Uranus – March 4th.

This is the closest planetary conjunction of the year. Use optical aid to find Uranus about .3° below Venus. Notice the stark difference in their brightness.

 © James R. Johnson, 2015
jim@jrjohnson.net

The Ecliptic – A Trace of the Sun’s Path across the Celestial Sphere

The title of this article is a concise and precise definition of the ecliptic, but further explanation is warranted. Before delving in, I recommend reviewing  the definition of a conceptual celestial sphere and reading Understanding a Star Chart  to prepare for the material presented in this article. Although the ecliptic is an important aspect of lunar and planetary observations, and seasons on the Earth, this article will concentrate on the Sun’s movement among the stars, and how that movement defines the ecliptic.

As the Earth proceeds through its annual journey in its orbit about the Sun, the Sun’s position among the background stars, as seen from Earth changes a little each day. Since we intuitively know that the Sun outshines all of the stars in the sky, so this seemingly makes no sense. But imagine the Sun as a disk no brighter than the Moon. We could then see the Sun and the “fixed” stars on the celestial sphere at the same time, and we could track the Sun’s movements among the stars on a day to day basis. In a year’s time after beginning this exercise, the Sun will have returned to the point at which it started and we will have traced out the full course of the ecliptic across the celestial sphere. The twelve constellations through which the Sun traverses during this annual journey are known as the zodiacal constellations.

sun_in_zodiac
The Solar Cycle. Addison-Wesley Longman. lasp.colorado.edu. Accessed by Jim Johnson on February 13, 2015.

The Sun in the preceding image is in a fixed position for the purpose of this discussion. The Earth orbits the Sun as indicated by the blue circle with dates indicating progress through one orbit over the course of a year. Consider the Earth’s position on the blue circle on March 21st. When viewed from the Earth on this date, the Sun appears in the constellation of Pisces. Now consider the Earth’s position six months later on September 21st, and trace a line from the Earth through the Sun to see that it would appear in the constellation of Virgo.

The specific line that the Sun seems to trace among the fixed stars on the celestial sphere as a result of Earth’s orbit about the Sun is called the ecliptic, and is indicated by the horizontally oriented sine wave on the flat projection map of the entire celestial sphere below. This is a great place to start an exploration of the ecliptic. This particular map is a scan of the actual constellation map carried aboard the Apollo 11 lunar expedition. First, let’s become familiar with this map.

Flown Version of LM G&N Dictionary, Apollo 11, Page S-1, May 29, 1969-BD. Private Collection. Scans Courtesy Larry McGlynn. https://www.hq.nasa.gov/alsj/a11/A11StarCharts.html. Accessed by Jim Johnson on July 18, 2014.
Flown Version of LM G&N Dictionary, Apollo 11, Page S-1, May 29, 1969-BD. Private collection scans courtesy of Larry McGlynn. https://www.hq.nasa.gov/alsj/a11/ A11StarCharts.html. Accessed by Jim Johnson on July 18, 2014.

The horizontal lines are representations of degrees of declination, with 0° declination, or the equator across the center of the page, and the north (+90° declination) and south poles (-90° declination) are at the top and bottom edges of the page, respectively. Note that the vertical lines representing hours of right ascension do not converge at the poles (top and bottom edges of the map), because this is a flat projection.

To more closely relate the flat projection map to the celestial sphere, note that the zero hour of right ascension on the right edge of the map and the 24th hour on the left edge of the map are one and the same, so the right and left edges of the map can be brought together with the observer in the imaginary center of the map tube that is formed. The implication of this is that if one’s point of gaze slips off of the left edge of the map at, say +40° declination, the point of gaze would immediately appear on the right edge at +40° declination.

Compare this map to the sky map that follows below, and that was discussed in Understanding a Star Chart. The sky maps are contained within a circle that represents the horizon, and the stars contained therein are the stars that can be seen above the horizon at a specific point in time.  The Apollo 11 flat projection, however, represents the entire celestial sphere. The ecliptic on the sky map below is designated by the yellow horizontal line that stretches from east to west, just north of the equator.

Let’s trace the ecliptic on the sky map below and compare the various aspects discussed with the Apollo 11 constellation chart above. Begin at the western horizon, where at that point the ecliptic lies south of the equator. Moving eastward (toward the left) along the ecliptic, notice that it crosses the equator (0°) at 0 hours (0h) of right ascension in the constellation of Pisces.  At 6 hours of right ascension (6h), the ecliptic reaches its farthest distance north of the equator in Gemini, at which point it begin converging on the equator again just below the eastern horizon at 12h. Note that the ecliptic transverses several zodiacal constellations on this map. From west to east, they are: Pisces, Aries, Taurus, Gemini, Cancer, and Leo.

Annotated_Sky_Map
Annotated Sky Map, Jim Johnson, December 27, 2015.

 

Now we are ready for a more thorough exploration of the ecliptic, which presents as a sine wave on the annotated Apollo 11 map below.

A11StarChart-S1 annotated by Jim JohnsonThe Sun’s journey from one end of the ecliptic to the other, or from the right edge of the map to the left edge of the map, is exactly one year, then the cycle repeats. There are four very important  points through which the Sun passes in its annual journey across the ecliptic. The two points at which the ecliptic intersects the equator (0h and 12h) are called equinox, and the points at which the ecliptic reach its farthest declination from the equator (6h and 18h) are called solstice. Let’s step through the Sun’s journey across the ecliptic as presented by starting at the left edge of the map.

1. The Sun’s arrival at the 0-hour of right ascension, or the intersection of the ecliptic and the celestial equator (0° declination), occurs around March 21st. This is known as the Vernal Equinox, or the beginning of astronomical spring. On the date of the equinox, the length of the day and the length of the night are about equal. Astronomical spring extends three months from this date while the Sun travels toward the intersection of the 6th hour of right ascension and +23° declination.

2. The Sun’s arrival at the 6th hour of right ascension coincides with it’s northern most declination of +23°. This point is known as the Summer Solstice, and it occurs around June 21st, marking the first day of astronomical summer. Astronomical summer extends for three months past this date as the Sun descends southward back toward the intersection of the ecliptic and the celestial equator at the 12th hour of right ascension.

3. The Autumnal Equinox is marked by the Sun’s arrival at the 12th hour of right ascension as it makes its south bound crossing of the celestial equator. This occurs on about September 21st each year, and is known as the first day of astronomical fall, which endures for three more months until the Sun reaches its southern most point on the ecliptic. For the second time in a year, the days and nights are of about equal length while the Sun is on or near the celestial equator.

4. The Winter Solstice is marked by the Sun’s arrival at the 18th hour of right ascension, and its most southward point on the ecliptic at -23° declination, on about December 21st each year. This is known as the astronomical beginning of Winter, which endures for the next three months as the Sun ascends northward toward the celestial equator.

As noted while describing the Sun’s travels from one edge of the map to the other, it also changes travels northward and then southward in declination from the equator reaching an maximum of +23° declination and -23° declination. This ±23° change of declination is related to the tilt of the Earth’s axis relative to the ecliptic, or the plane of the solar system, and this north and south movement of the sun is related to our four seasons on Earth. This topic will be addressed more thoroughly in The Ecliptic and the Four Seasons. The planets “wanderings” among the fixed stars is also related to the ecliptic, and this topic will be addressed more thoroughly in The Ecliptic and the Motions of the Planets. Look for these two articles in the coming months.

© James R. Johnson, 2015.
jim@jrjohnson.net