Thursday, October 20
James Chadwick (1891-1974), English physicist who discovered the neutron, was born 125 years ago.
Orionid Meteor Shower (radiant rises at 10:14 p.m.; but so does the Moon at 10:17 p.m.; radiant altitude 18° at midnight, the expected worldwide peak)
Friday, October 21
Orionid Meteor Shower (36 meteors per hour, or less; radiant transits the meridian at 5:19 a.m., altitude 63°; radiant altitude at the beginning of morning twilight is 62°)
The Moon reaches its most northerly declination this month at 4:25 a.m. (+18° 05' 51.00", in Gemini).
The Turtle Lake meteorite fall occurred, penetrating the windshield of a car near Clayton, Wisconsin, 20 years ago (1996).
The International Space Station will cross the sky from 6:59:14 to 7:02:29 p.m. (W to SW). Peak magnitude: -0.2; Highest altitude: 13°. Closest distance: 788 miles. Nautical twilight. 7:00:42 p.m. above Venus; 7:01:00 above Saturn; 7:02:04 teapot spout of Sagittarius.
The Milky Way in Cygnus passes through the zenith at the end of evening twilight.
Saturday, October 22
The 18.6-magnitude Jupiter Trojan asteroid 6997 Laomedon may pass in front of the 10.4-magnitude star Tycho 195-1509-1 in Canis Minor (δ=+0.6°; spectral type unknown; 1,044-2,176 ly) for up to 1.6 seconds around 5:46:17 a.m. ± 48s, as astronomical twilight begins. Probability of seeing the event along the predicted centerline is 1.3%.
Last Quarter Moon; rises 11:17 p.m. Friday; transits 6:42 a.m.; sets 2:03 p.m.; δ = +16° in Cancer
David E. Hadden (1866-1943), Alta, Iowa amateur astronomer and citizen scientist, was born in Ireland 150 years ago.
Sunday, October 23
The 20.2-magnitude unnamed asteroid 82004 (2000 QA226) may pass in front of the 8.8-magnitude star HD 188048 in Sagittarius (δ=-25.2°; K1III; 4,972-26,135 ly) for up to 0.4 seconds around 8:55:37 p.m. ± 20s. Probability of seeing the event along the predicted centerline is 0.7%.
Monday, October 24
Leonis Minorid meteors may be seen around this date (3 meteors per hour, or less; expected worldwide peak around midnight; radiant rises at 12:32 a.m.; radiant altitude 5° at moonrise at 1:21 a.m.; radiant altitude 47° as morning twilight begins).
The 20.7-magnitude unnamed outer main-belt asteroid 99859 (2002 OG21) may pass in front of the 9.7-magnitude star Tycho 827-906-1 in Leo (δ=+12.7°; spectral type unknown; 240-256 ly) for up to 0.3 seconds around 3:38:49 a.m. ± 20s. Probability of seeing the event along the predicted centerline is 0.7%.
MESSENGER made it's first gravity-assist flyby of Venus at a distance of 1,859 miles, 10 years ago (2006).
Gene Roddenberry (1921-1991), creator of Star Trek, died 25 years ago.
The 17.7-magnitude asteroid 3297 Hong Kong may pass in front of the 10.1-magnitude star HD 358568 in Capricornus (δ=-19.2°; K7; 1,661-13,653 ly) for up to 1.3 seconds around 7:18:32 p.m. ± 31s, during astronomical twilight. Probability of seeing the event along the predicted centerline is 1.7%.
Tuesday, October 25
Regulus is near the Moon this morning before dawn.
The STEREO A & B solar observatories were launched 10 years ago (2006).
Wednesday, October 26
The United States finished the last year of 26 or 27 weeks of daylight saving time, 30 years ago (1986). We now have 34.
The Kyushu meteorite fall occurred in Japan, 130 years ago (1886).
Theodor von Oppolzer (1841-1886), Austrian astronomer and mathematician, was born 175 years ago.
Venus is nearest Antares today during evening twilight, low in the SW.
The Iridium 75 satellite will sunglint to -3.2 magnitude around 8:04:00 p.m. at azimuth 18° (NNE) and altitude 32° (809 miles), in Camelopardalis, between Polaris and Capella.
Thursday, October 27
"Milky Way Archaeology with APOGEE and Kepler" by Jennifer Johnson, Professor of Astronomy, Ohio State University, 4421 Sterling Hall, UW-Madison, 3:30 - 5:00 p.m.
Last week, we looked at the radial velocities and parallaxes of the stars in the Coathanger asterism, a prominent binocular object in the constellation Vulpecula. Parallaxes (and therefore distances) can only be accurately measured out to a few hundred light years, but radial velocity, in principle, can be accurately measured out to any distance, provided you can collect enough light to get a decent spectrum. Radial velocity can thus be used as a powerful discriminant to determine whether a group of stars are members of a star cluster. If they are, their radial velocities should be similar.
Seeing that the stars of The Coathanger have disparate values for both radial velocity and parallax, we could pretty easily determine that The Coathanger is an asterism—a chance juxtaposition of stars at widely varying distances—rather than a star cluster where the stars are all at nearly the same distance.
Proper motion in right ascension (α) and declination (δ) is the measured motion of a star upon the plane of the sky in milliarcseconds per year. With these two proper motion values and radial velocity (all three orthogonal to each other), one can easily determine the true space motion of the star. Proper motion, like parallax, can usually only be accurately measured out to a few hundred or perhaps thousand light years.
Here are the proper motions for the stars in The Coathanger. Not only are the proper motions all over the map—lending further evidence that The Coathanger is not a star cluster—but we also see that the weak evidence we presented last week for a possible association between HR 7391 & HD 182620 and HR 7364 & HD 182972 evaporates completely when comparing the proper motions of these two pairs of stars. Moreover, it looks like HD 182293 and HR 7385 (highlighted in red below) might possibly be high-velocity stars—hardly members of any putative star cluster.
Now, let's take a look at the same data for the ten most prominent members of The Pleiades star cluster.
Clearly, the radial velocities, parallaxes, and proper motions of these Pleiades stars are very similar, indicating they are all about the same distance and traveling through space together, demonstrating that they are members of a true star cluster.
Lest there be any doubt, let's take a look at a plot of radial velocity vs. parallax for The Pleiades as we did last week for The Coathanger. There is no doubt that these Pleiades stars are part of a bona fide star cluster!
As Dodgeville (and many other towns) are planning to replace their streetlights with LED luminaires, it is imperative that the LEDs that are used have a CCT (correlated color temperature) of 3000 K or less. This is a "warm" white light (similar to incandescent) rather than the "cold" blue-rich light often seen with LEDs. On June 14, 2016, the American Medical Association issued guidance on this subject.
"Discomfort and disability from intense, blue-rich LED lighting can decrease visual acuity and safety, resulting in concerns and creating a road hazard."For your residential lighting needs, a good local source for LED bulbs that are not blue-rich is Madison Lighting. They have many LED bulbs in both 3000 K and 2700 K. I use 2700K bulbs exclusively in my home, and the warm white light they provide is an excellent replacement for incandescent and compact fluorescent bulbs. Wherever you buy them, I suggest you purchase a 2700K bulb and a 4000K bulb (a CCT that is often used for roadway lighting) and compare them in your home. I believe that you will much prefer the 2700K lighting. If 2700K lighting is best for your home, then why should it not be best for outdoor lighting as well? If you have ever been irritated at night by an oncoming vehicle with those awful "blue" headlights, you've experienced firsthand why blue-rich light in our nighttime environment must be minimized."In addition to its impact on drivers, blue-rich LED streetlights operate at a wavelength that most adversely suppresses melatonin during night. It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps. Recent large surveys found that brighter residential nighttime lighting is associated with reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning and obesity."
"The detrimental effects of high-intensity LED lighting are not limited to humans. Excessive outdoor lighting disrupts many species that need a dark environment. For instance, poorly designed LED lighting disorients some bird, insect, turtle and fish species, and U.S. national parks have adopted optimal lighting designs and practices that minimize the effects of light pollution on the environment."
"Recognizing the detrimental effects of poorly-designed, high-intensity LED lighting, the AMA encourages communities to minimize and control blue-rich environmental lighting by using the lowest emission of blue light possible to reduce glare. The AMA recommends an intensity threshold for optimal LED lighting that minimizes blue-rich light. The AMA also recommends all LED lighting should be properly shielded to minimize glare and detrimental human health and environmental effects, and consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time periods."
When gazing toward the watered-down zodiacal constellation Aquarius, I always look for the Water Jar. But at last Saturday's star party at Governor Dodge State Park, eagle-eyed Jackie Passant found a compact little group of stars in Aquarius for us that resides between the Circlet of Pisces and Fomalhaut. I'd like to suggest a name for them: The Water Drop.
The stars that make up this diminutive jewel are four: ψ1, ψ2, ψ3, and χ (ψ=Psi, χ=Chi).
Are the Water Drop stars a teeny cluster or association?
Most assuredly not, though another fine example of celestial serendipity!
