Already early this week you will see an occasional Perseid meteor gracing the sky, but next weekend the real show begins. The absolute peak of this year’s Perseids is favorable to observers in North America, and with no moonlight interference we are in for a real treat—provided you escape cloudy weather. I highly recommend “going mobile” if the weather forecast 24-48 hours before the peak night indicates less than ideal conditions at your location.
The Perseids this year are expected to peak Sunday night August 12/13. Highest observed rates will likely be between 2 a.m. and 4 a.m. Monday, August 13. Here’s a synopsis of the 2018 Perseids.
Many years ago I wrote a short poem while listening to the final and most otherworldly section of The Planets by Gustav Holst: Neptune, the Mystic.
Here it is:
Neptune, the Mystic from The Planets by Gustav Holst
Royal Philharmonic Orchestra, Vernon Handley
Ambrosian Chorus, John McCarthy
Alto ALC 1013
The endless poetry of space Sends shivers across my spine,
And there upon the threshold sounds The now distant drone of time.
Music fills the spacecraft Starlight fills the night,
And there upon the threshold think I wonder, was I right?
The Planets was written by Holst between 1914 and 1916, and the premiere performance was at The Queen’s Hall, London, on September 29, 1918. Adrian Boult conducted the orchestra in a private performance for about 250 invited guests. The Queen’s Hall was destroyed by an incendiary bomb during the London Blitz in 1941, seven years after Holst’s death in 1934.
Pluto was discovered by Clyde Tombaugh in 1930, and was considered to be the ninth planet until its controversial demotion by the IAU in 2006. A number of composers have added a Pluto movement to ThePlanets (“Pluto, the Renewer” by Colin Matthews, for example), and even an improvised performance (“Pluto, the Unpredictable”) by Leonard Bernstein and the New York Philharmonic. I remember enjoying “Pluto, the Unknown” by American composer Peter Hamlin performed by the Des Moines Symphony in 1992, but unfortunately no recording of this work exists.
Here is a table of the 12 largest satellites in our solar system. In addition to the size of each satellite, its home planet, its median distance from that planet, and discovery information, its median distance from its home planet is given in terms of the median lunar distance from the Earth. Remarkably, Pluto’s moon Charon is just 0.05 lunar distances from Pluto, only 19,591 km. Only one other of the largest satellites orbits closer to its home planet than the Moon orbits around the Earth, and that is Neptune’s moon Triton at 92% of the Earth-Moon distance. At the other end of the scale, Saturn’s moon Iapetus orbits Saturn over nine times further away than the Moon orbits the Earth.
Now let’s look at the orbital eccentricity of each of the largest moons, and the orbital inclination relative to the equator of its home planet.
Our familiar Moon is really an oddball: it has the greatest orbital eccentricity of all the largest satellites, and, with the exception of Triton and Iapetus, by far the greatest orbital inclination relative to the equator of its home planet. Triton is the oddball among oddballs as it is the only large satellite in our solar system that has a retrograde orbit: it orbits Neptune in a direction opposite the planet’s rotation. Iapetus has an orbital inclination relative to Saturn’s equator almost as much as the Moon’s orbital inclination relative to the Earth’s equator, but this anomaly can perhaps be forgiven because Iapetus orbits so very far away from Saturn. Its orbital period is over 79 days.
Note that the Moon’s orbital inclination relative to the equator of the Earth varies between 18.33˚ and 28.60˚. This occurs because the intersection between the plane of the Moon’s orbit around the Earth and the plane of the Earth’s orbit around the Sun precesses westward, making an entire circuit every 18.6 years.
Of all the constellations in our sky, only one is a musical instrument: Lyra the Lyre. A lyre is a stringed harplike instrument used to accompany a singer or reader of poetry, especially in ancient Greece. One wonders what strange and lonely enchantments await the contemplative listener as Lyra wheels through our zenith these short summer nights.
Nova Scuti 2018 (or N Sct 2018, for short) was discovered by prolific nova finder Yukio Sakurai of Japan on June 29, 2018. His discovery image at 13:50:36 UT showed the nova shining at magnitude 10.3 (unfiltered CCD magnitude), using only a 180-mm f/2.8 lens plus a Nikon D7100 digital camera. One of his many discoveries is named after him: Sakurai’s Object.
What is a nova? A classical nova is a close binary star system that includes a white dwarf and a “normal” star. The white dwarf siphons material off the other star until a critical density and temperature is reached in the atmosphere of the white dwarf, and a thermonuclear detonation occurs.
Nova Scuti 2018 will eventually receive a variable star designation (V507 Sct?). Here are some typical nova light curves.
Nova Scuti 2018 is located fortuitously close to the 4.7-magnitude star Gamma (γ) Scuti.
Here is a time sequence of images I’ve acquired of Nova Scuti 2018. Comparing with the star chart above, can you find the nova?
Norwegian composer Edvard Grieg (1843-1907) is best known for his iconic Piano Concerto in A minor, op. 16, written in 1868 when the composer was just 24 years old, and his Peer Gynt suites, No. 1, op. 46 (1875, 1888), and No. 2, op. 55 (1875, 1891). Like Tchaikovsky, Grieg had a gift for melody.
Grieg once wrote, “Artists like Bach and Beethoven erected churches and temples on the heights. I only wanted to build dwellings for men in which they might feel happy and at home.” With this in mind, you will find no better introduction to some of the other gorgeous music that Grieg wrote than Norwegian conductor Bjarte Engeset conducting Sweden’s Malmö Symphony Orchestra on Naxos 8.572403.
Seldom have I found a disc of music so beautifully paced and played. These five pieces for string orchestra (augmented by oboe and horn on “Evening in the Mountains”) followed by one piece for full orchestra provide the listener with over 71 minutes of pure enjoyment that will convince you (if you weren’t already convinced) that Grieg deserves a place alongside the most significant composers of the late 19th and early 20th centuries. For me, personally, every one of these pieces is a favorite. There is nothing to skip over here!
Two Elegiac Melodies, op. 34 (1880)
+ The Wounded Heart
+ The Last Spring
Two Melodies for String Orchestra, op. 53 (1890)
+ The First Meeting
From Holberg’s Time: Suite in Olden Style, op. 40 (1884)
Two Lyric Pieces, op. 68 (1897-1899)
+ Evening in the Mountains
+ At the Cradle
Two Nordic Melodies for String Orchestra, op. 63 (1895)
+ In Folk Style
+ Cow-Call & Peasant Dance
Lyric Suite, op. 54 (1905)
+ Shepherd Boy
+ March of the Dwarves
Don’t let words like “gorgeous” and “pure enjoyment” give you the impression that this music is lightweight fare. There is a sadness in this beautiful music that evinces that it is anything but superficial. Grieg and his wife Nina lost their only child, Alexandra, to meningitis when she was little more than a year old, Nina later miscarried a second child, and Grieg himself suffered all his adult life from the effects of pleurisy he had contracted when he was 17 years old.
A 17th-magnitude dwarf star in Leo 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.
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
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.
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.
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
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
α = 18h 21m 01.6467s
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 01.6388s
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.