Caffau’s Star

A 17th-magnitude dwarf star in Leo 4,445^{+529}_{-427} ly distant has the lowest metallicity of any star yet discovered.  Stars with very low metallicity are designated as extremely metal-poor (EMP).

SDSS J102915+172927 (aka UCAC3 215-112497, UCAC4 538-051259, Gaia DR2 3890626773968983296, or just J1029+1729 for short) was identified by Elisabetta Caffau and her team in 2011 to have a global metallicity of Z ≤ 6.9 × 10-7 which means that the star is 99.999931% hydrogen and helium.  Looking at this another way, the global metallicity of our Sun is 0.0134 (98.66% hydrogen and helium), so Caffau’s Star has only about 1/19,000th the abundance of elements heavier than helium in comparison to the Sun.

Caffau’s Star   α2000 = 10h29m15.14913s   δ2000 = +17° 29′ 27.9267″

Metallicity is usually expressed as the abundance of iron relative to hydrogen.   It is a logarithmic scale.  [Fe/H] = 0.0 for the Sun; positive numbers mean iron is more abundant and negative numbers mean iron is less abundant than in the Sun.

[Fe/H] = +2.0 means iron is 100 times more abundant than in the Sun

[Fe/H] = +1.0 means iron is 10 times more abundant than in the Sun

[Fe/H] = -1.0 means iron is 1/10 as abundant as in the Sun

[Fe/H] = -2.0 means iron is 1/100 as abundant as in the Sun

And so on.  Caffau’s Star has an iron abundance [Fe/H] = -5.0, or 1/100,000th that of the Sun.  Caffau’s Star is the only EMP star with [Fe/H] < -4.5 thus far detected that is not a carbon-enhanced metal-poor star (CEMP).  In fact, Caffau’s Star has no detectable carbon!  Nor nitrogen.  Nor lithium.

Caffau’s Star is probably almost as old as our Milky Way galaxy.  In order to have survived for 13 Gyr, its mass cannot be any larger than 0.8 M.

Aguado, D.S., Prieto, C.A., Hernandez, J.I.G., et al. 2018 ApJL, 854, L34
Aguado, D.S., Prieto, C.A., et al. 2018 ApJL, 852, L20
Aguado, D. S., González Hernández, J. I., et al. 2017, A&A, 605, A40
Bonifacio, P., Caffau, E., Spite, M., Spite, F., François, P., et al. 2018
Caffau, E., Bonifacio, P., François, P., et al. 2011, NAT, 477, 67

June Boötids

Some meteor showers give a more-or-less reliable performance the same time each year, but others have an occasional year with (sometimes substantial) activity punctuating many years with little or no activity.  The June Boötids, which may or may not be visible any night this week but most likely Wednesday morning or Wednesday evening if at all, is one such shower.  This year, however, any meteors that do occur will be compromised by the nearly-full moon.

One hallmark of the June Boötids is that they are unusually slow meteors, so they’re easy to identify if you see one.  Look for the meteors to emanate from a region of the sky a few degrees north of the top of the “kite” of Boötes.

Of the 38 meteor showers listed in the IMO‘s “Working List of Visual Meteor Showers”, the lowest V, which is the pre-atmospheric Earth-apparent meteor velocity, is 18 km/s.  The three showers with that velocity are the π Puppids (Apr 23, δ=-45°), June Boötids (Jun 27, δ=+48°), and Phoenicids (Dec 2, δ=-53°).  For those of us living in the northern U.S., the June Boötids is the only one of these three showers we are ever likely to see.

Outbursts of June Boötids activity approaching or even exceeding 100 meteors per hour (single observer hourly rate) occurred in 1916, 1921, 1927, 1998, and 2004.  When the next outburst will occur none can yet say.

In eight years between 2001 and 2014 inclusive, my friend and expert visual meteor observer Paul Martsching of Ames, Iowa observed fourteen 0-magnitude or brighter June Boötids, the brightest of which was -4 in 2004.  He has seen June Boötids activity as early as June 22nd and as late as July 1st.  Of the 44 June Boötids he has observed, 52% were white in color, 27% yellow, and 21% orange.

Though we’re always at the mercy of the weather and the Moon and a workaday world that does little to accommodate the observational astronomy amateur scientist, meteor watching is a rewarding activity.   Even when meteor activity is sparse, you have time to think, to study the sky, to experience the beauty of the night.

Bad Lighting at Dodgeville High School

At a school board meeting in November 2017, concerns were raised about inadequate lighting for evening school events, so the Dodgeville School District directed Alliant Energy to install some additional lights.  The lighting was installed during a warm spell in January 2018, and the photographs you see below were taken during the afternoon and evening of June 17, 2018.

Rather than being used only when school events are taking place in the evening, these terrible lights are on dusk-to-dawn 365 nights a year.  They are too bright, poorly directed, poorly shielded, and the glare they cause on W. Chapel St. and N. Johnson St. could pose a safety concern for pedestrians not being seen by drivers experiencing disability glare.  I can imagine that adjacent neighbors are not too happy with the light trespass into their yards and residences, either.

This is a perfect example of poor lighting design and unintended consequences.  How could it be done better?  Look for the solution below the following series of photos documenting the problem.

Bleacher path floodlight produces a great deal of uplight, and illuminates the disc golf course far more than the bleacher path
Bleacher path floodlight is mounted in a nearly-horizontal orientation
Bleacher path floodlight
Bleacher path floodlight
Bleacher path looking towards the bleachers


Bleacher path looking towards W. Chapel St.


Bleacher path at night
Bleacher path floodlight lighting up the disc golf course. Also note how much brighter the illumination is from the newly-installed blue-white LED streetlight as compared with the orangish light from the older high pressure sodium (HPS) luminaire.
Bleacher path floodlight lighting up the disc golf course and basket
Large tree being brightly illuminated all night long with bleacher path in foreground
Sub-optimal parking lot lighting at Dodgeville High School
Overflow parking floodlight


Two additional overflow parking lot floodlights
Overflow parking floodlight


Overflow parking floodlights


Overflow parking floodlight glare and spill light


Overflow parking floodlight glare onto W. Chapel St. in Dodgeville
Overflow parking glare and spill light onto W. Chapel St. in Dodgeville


Pedestrian-scale 2700K LED “soft” lighting could be installed along the bleacher path
Or vandal-resistant bollards could be used—even low voltage lighting
If floodlights must be used, shield them, point them more downwards, and turn them off after 11:00 p.m. each night (or have them on only while evening school events are in progress)

In fact, regardless of the lighting solution, the lights should be either turned off or dimmed down to a lower level later at night.  (Security cameras will see just fine at lower light levels if that is a concern.)

Good neighbor outdoor lighting means minimizing GLUT:

Glare—never helps visibility
Light Trespass—no point in putting light where it is not needed
Uplight—sending light directly up into the night sky is a total waste
Too Much Light—use the right amount of light for the task, don’t overlight

29769 (1999 CE28)

Early in the morning of Tuesday, May 29, 2018, I was fortunate enough to record a 3.2 second occultation of the 12.6 magnitude star UCAC4 359-140328 in Sagittarius by the unnamed asteroid 29769, originally given the provisional designation 1999 CE28.

Not only is this the first time this asteroid has been observed to pass in front of a star, it is the smallest asteroid I have ever observed passing in front of a star.  At an estimated diameter of 14.7 miles, had I been located just 7.4 miles either side of the centerline of the shadow path, I would have missed this event altogether!  This is also the first positive event I’ve recorded for an (as yet) unnamed asteroid, and the first positive event I’ve recorded for an asteroid having more than a four-digit number (29769).

As you can see in the map above, the predicted shadow path was quite a ways northwest of my location.  Even though I used the Gaia DR2 position for UCAC4 359-140328 for the path prediction, the existing orbital elements for asteroid 29769 did not yield a correspondingly accurate position for the asteroid.

Though a single chord across an asteroid does not give us any definitive information about its overall size and shape, it does give us a very accurate astrometric position that will be used to improve the orbital elements for this asteroid.

The central moment of this occultation event was 6:00:02.414 UT on May 29, 2018, which was about 20 seconds later than predicted.  The astrometric equatorial coordinates for the star UCAC4 359-140328 referenced to the J2000 equinox (using Gaia DR2 with proper motion applied) are

UCAC4 359-140328
α = 18h 21m 01.6467
δ = -18° 20′ 46.282″


Using JPL Horizons (with the extra precision option selected), the astrometric equatorial coordinates for the asteroid 29769 (1999 CE28), again referenced to the J2000 equinox, are

29769 (1999 CE28)
α = 18h 21m 01.6388
δ = -18° 20′ 46.320″


As we can see above, the actual position of the asteroid at the time of the event was 0.0079 seconds of time east and 0.038 seconds of arc north of its predicted position.  This observation will provide a high quality astrometric data point for the asteroid that will be used to improve its orbit.  Gratifying!

As of this writing, there are 523,584 minor planets that have sufficiently well enough determined orbits to have received a number.  Of these, only 21,348 have received names (4.1%).  So, I guess you could say there is quite a backlog of numbered asteroids awaiting to receive names.  The IAU should consider naming some minor planets after the most productive asteroid occultation observers around the world.  There aren’t very many of us, and this would certainly be an encouragement to new and existing observers.

Project Gutenberg

Over 56,000 historical books and other documents, most published prior to 1923, are available online for downloading or browsing at Project Gutenberg (, with more being added all the time. A quick search of the term “astronomy” yields the following:

The Discovery of a World in the Moone: Or, A Discovrse Tending To Prove That ‘Tis Probable There May Be Another Habitable World In That Planet (1638)
John Wilkins (1614-1672)

The Study of Astronomy, Adapted to the capacities of youth (1796)
John Gabriel Stedman (1744-1797)

The Martyrs of Science, or, The lives of Galileo, Tycho Brahe, and Kepler (1841)
David Brewster (1781-1868)

Lectures on Astronomy (1854)
The Wit and Humor of America, Volume V. (1911)
George Horatio Derby (1823-1861), writing under the name of John Phoenix
Marshall Pinckney Wilder (1859-1915), editor

Letters on Astronomy: In which the Elements of the Science are Familiarly Explained in Connection with Biographical Sketches of the Most Eminent Astronomers (1855)
Denison Olmsted (1791-1859)

The Uses of Astronomy: An Oration Delivered at Albany on the 28th of July, 1856 (1856)
Edward Everett (1794-1865)

Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1 (1858)
Alexander von Humboldt (1769-1859)

Curiosities of Science, Past and Present: A Book for Old and Young (1858)
John Timbs (1801-1875)

Astronomy for Young Australians (1866)
James Bonwick (1817-1906)

Meteoric astronomy: A treatise on shooting-stars, fire-balls, and aerolites (1867)
Daniel Kirkwood (1814-1895)

Popular Books on Natural Science: For Practical Use in Every Household, for Readers of All Classes (1869)
Aaron David Bernstein (1812-1884)

Half-hours with the Telescope: Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction (1873)
Richard Anthony Proctor (1837-1888)

Astronomical Myths: Based on Flammarions’s “History of the Heavens” (1877)
John Frederick Blake (1839-1906)
Camille Flammarion (1842-1925)

New and Original Theories of the Great Physical Forces (1878)
Henry Raymond Rogers (1822-1901)

Recreations in Astronomy: With Directions for Practical Experiments and Telescopic Work (1879)
Henry White Warren (1831-1912)

The Sidereal Messenger of Galileo Galilei and a Part of the Preface to Kepler’s Dioptrics Containing the Original Account of Galileo’s Astronomical Discoveries (1880)
Galileo Galilei (1564-1642)
Johannes Kepler (1571-1630)
Edward Stafford Carlos ((1842–1927), translator

Sir William Herschel: His Life and Works (1880)
Edward Singleton Holden (1846-1914)

Popular Scientific Recreations in Natural Philosophy, Astronomy, Geology, Chemistry, etc., etc., etc. (1881)
Gaston Tissandier (1843-1899)

Publications of the Astronomical Society of the Pacific, Volume 1 (1889)
Astronomical Society of the Pacific (1889-)

A Textbook of General Astronomy for Colleges and Scientific Schools (1889)
Charles Augustus Young (1834-1908)

Time and Tide: A Romance of the Moon (1889)
Robert Stawell Ball (1840-1913)

Astronomy with an Opera-glass: A Popular Introduction to the Study of the Starry Heavens with the Simplest of Optical Instruments (1890)
Garrett Putman Serviss (1851-1929)

Pioneers of Science (1893)
Sir Oliver Joseph Lodge (1851-1940)

Great Astronomers (1895)
Robert Stawell Ball (1840-1913)

The Astronomy of Milton’s ‘Paradise Lost’ (1896)
Thomas Nathaniel Orchard, M.D.

Myths and Marvels of Astronomy (1896)
Richard Anthony Proctor (1837-1888)

The Story of Eclipses (1899)
George Frederick Chambers (1841-1915)

The Tides and Kindred Phenomena in the Solar System: The Substance of Lectures Delivered in 1897 at the Lowell Institute, Boston, Massachusetts (1899)
Sir George Howard Darwin (1845-1912)

The Royal Observatory, Greenwich: A Glance at Its History and Work (1900)
Edward Walter Maunder (1851-1928)

The Story of the Heavens (1900)
Robert Stawell Ball (1840-1913)

Other Worlds: Their Nature, Possibilities and Habitability in the Light of the Latest Discoveries (1901)
Garrett Putman Serviss (1851-1929)

Pleasures of the telescope: An Illustrated Guide for Amateur Astronomers and a Popular Description of the Chief Wonders of the Heavens for General Readers (1901)
Garrett Putman Serviss (1851-1929)

A Text-Book of Astronomy (1903)
George Cary Comstock (1855-1934)

Astronomical Discovery (1904)
Herbert Hall Turner (1861-1930)

A New Astronomy (1906)
David Peck Todd (1855-1939)

New Theories in Astronomy (1906)
William Stirling (1822-1900)

Side-Lights on Astronomy and Kindred Fields of Popular Science (1906)
Simon Newcomb (1835-1909)

The Children’s Book of Stars (1907)
Geraldine Edith Mitton (1868-1955)

Mathematical Geography (1907)
Willis Ernest Johnson (1869-1951)

Astronomical Instruments and Accessories (1908)
William Gaertner and Company (1896-)
now Gaertner Scientific Corporation

The Astronomy of the Bible: An Elementary Commentary on the Astronomical References of Holy Scripture (1908)
Edward Walter Maunder (1851-1928)

A Popular History of Astronomy During the Nineteenth Century, Fourth Edition (1908)
Agnes Mary Clerke (1842-1907)

Astronomical Curiosities: Facts and Fallacies (1909)
John Ellard Gore (1845-1910)

The Future of Astronomy (1909)
Edward Charles Pickering (1846-1919)

History of Astronomy (1909)
George Forbes (1849-1936)

Astronomy for Amateurs (1910)
Camille Flammarion (1842-1925)

Astronomy of To-day: A Popular Introduction in Non-Technical Language (1910)
Cecil Goodrich Julius Dolmage (1870-1908)

The World’s Greatest Books — Volume 15 — Science (1910)
Arthur Mee (1875-1943), editor
Sir John Alexander Hammerton (1871-1949), editor

The Science of the Stars (1912)
Edward Walter Maunder (1851-1928)

Are the Planets Inhabited? (1913)
Edward Walter Maunder (1851-1928)

Woman in Science: With an Introductory Chapter on Woman’s Long Struggle for Things of the Mind (1913)
John Augustine Zahm (1851-1921), writing under the name H. J. Mozans

A Field Book of the Stars (1914)
William Tyler Olcott (1873-1936)

An Introduction to Astronomy (1916)
Forest Ray Moulton (1872-1952)

Scientific Papers by Sir George Howard Darwin. Volume V. Supplementary Volume (1916)
Sir George Howard Darwin (1845-1912)
Ernest William Brown (1866-1938), contributor
Sir Francis Darwin (1848-1925), contributor

The gradual acceptance of the Copernican theory of the universe (1917)
Dorothy Stimson (1890-1988)

Astronomical Lore in Chaucer (1919)
Florence Marie Grimm

Lectures on Stellar Statistics (1921)
Carl Vilhelm Ludwig Charlier (1862-1934)

The Star People (1921)
Gaylord Johnson

Terrestrial and Celestial Globes Volume 1: Their History and Construction Including a Consideration of their Value as Aids in the Study of Geography and Astronomy (1921)
Edward Luther Stevenson (1858-1944)

Terrestrial and Celestial Globes Volume 2: Their History and Construction Including a Consideration of their Value as Aids in the Study of Geography and Astronomy (1921)
Edward Luther Stevenson (1858-1944)

Astronomy for Young Folks (1922)
Isabel Martin Lewis (1881-1966)

Astronomy: The Science of the Heavenly Bodies (1922)
David Peck Todd (1855-1939)

The New Heavens (1922)
George Ellery Hale (1868-1938)

Watchers of the Sky (1922)
Alfred Noyes (1880-1958)

Biography of Percival Lowell (1935)
Abbott Lawrence Lowell (1856-1943)

Like Sun, Like Moon

The Earth orbits the Sun once every 365.256363 (mean solar) days relative to the distant stars.  The Earth’s orbital speed ranges from 18.2 miles per second at aphelion, around July 4th, to 18.8 miles per second at perihelion, around January 3rd.  In units we’re perhaps more familiar with, that’s 65,518 mph at aphelion and 67,741 mph at perihelion. That’s a difference of 2,223 miles per hour!

As we are on a spinning globe, the direction towards which the Earth is orbiting is different at different times of the day.  When the Sun crosses the celestial meridian, due south, at its highest point in the sky around noon (1:00 p.m. daylight time), the Earth is orbiting towards your right (west) as you are facing south. Since the Earth is orbiting towards the west, the Sun appears to move towards the east, relative to the background stars—if we could see them during the day.  Since there are 360° in a circle and the Earth orbits the Sun in 365.256363 days (therefore the Sun appears to go around the Earth once every 365.256363 days relative to the background stars), the Sun’s average angular velocity eastward relative to the background stars is 360°/365.256363 days = 0.9856° per day.

The constellations through which the Sun moves are called the zodiacal constellations, and historically the zodiac contained 12 constellations, the same number as the number of months in a year.  But Belgian astronomer Eugène Delporte (1882-1955) drew up the 88 constellation boundaries we use today, approved by the IAU in 1930, so now the Sun spends a few days each year in the non-zodiacal constellation Ophiuchus, the Serpent Bearer. Furthermore, because the Earth’s axis is precessing, the calendar dates during which the Sun is in a particular zodiacal constellation is gradually getting later.

Astrologically, each zodiacal constellation has a width of 30° (360° / 12 constellations = 30° per constellation).  But, of course, the constellations are different sizes and shapes, so astronomically the number of days the Sun spends in each constellation varies. Here is the situation at present.

Sun Travel Dates
Sea Goat
Jan 19 through Feb 16
Water Bearer
Feb 16 through Mar 12
The Fish
Mar 12 through Apr 18
The Ram
Apr 18 through May 14
The Bull
May 14 through Jun 21
The Twins
Jun 21 through Jul 20
The Crab
Jul 20 through Aug 10
The Lion
Aug 10 through Sep 16
The Virgin
Sep 16 through Oct 31
The Scales
Oct 31 through Nov 23
The Scorpion
Nov 23 through Nov 29
Serpent Bearer
Nov 29 through Dec 18
The Archer
Dec 18 through Jan 19


The apparent path the Sun takes across the sky relative to the background stars through these 13 constellations is called the ecliptic.  A little contemplation, aided perhaps by a drawing, will convince you that the ecliptic is also the plane of the Earth’s orbit around the Sun.  The Moon never strays very far from the ecliptic in our sky, since its orbital plane around the Earth is inclined at a modest angle of 5.16° relative to the Earth’s orbital plane around the Sun.  But, relative to the Earth’s equatorial plane, the inclination of the Moon’s orbit varies between 18.28° and 28.60° over 18.6 years as the line of intersection between the Moon’s orbital plane and the ecliptic plane precesses westward along the ecliptic due to the gravitational tug of war the Earth and the Sun exert on the Moon as it moves through space.  This steep inclination to the equatorial plane is very unusual for such a large moon.  In fact, all four satellites in our solar system that are larger than our Moon (Ganymede, Titan, Callisto, and Io) and the one that is slightly smaller (Europa) all orbit in a plane that is inclined less than 1/2° from the equatorial plane of their host planet (Jupiter and Saturn).

Since the Moon is never farther than 5.16° from the ecliptic, its apparent motion through our sky as it orbits the Earth mimics that of the Sun, only the Moon’s angular speed is over 13 times faster, completing its circuit of the sky every 27.321662 days, relative to the distant stars.  Thus the Moon moves a little over 13° eastward every day, or about 1/2° per hour.  Since the angular diameter of the Moon is also about 1/2°, we can easily remember that the Moon moves its own diameter eastward relative to the stars every hour.  Of course, superimposed on this motion is the 27-times-faster-yet motion of the Moon and stars westward as the Earth rotates towards the east.

Now, take a look at the following table and see how the Moon’s motion mimics that of the Sun throughout the month, and throughout the year.

——— Moon’s Phase and Path ———
Sun’s Path
Mar 20
Jun 21
Sep 22
Dec 21


New = New Moon
near the Sun
FQ = First Quarter
90° east of the Sun
Full = Full Moon
180°, opposite the Sun
LQ = Last Quarter
90° west of the Sun


= crosses the celestial equator heading north
= rides high (north) across the sky
= crosses the celestial equator heading south
= rides low (south) across the sky


So, if you aren’t already doing so, take note of how the Moon moves across the sky at different phases and times of the year.  For example, notice how the full moon (nearest the summer solstice) on June 27/28 rides low in the south across the sky.  You’ll note the entry for the “Jun 21” row and “Full” column is “Low”.  And, the Sun entry for that date is “High”.  See, it works!