TSTW 5/1/08
Thursday, May 1
The Iridium 65 satellite will flare to -6 magnitude around 11:30 p.m. at azimuth 247° (WSW) and altitude 13°, in Hydra.
The Moon crosses the celestial equator heading north.
Friday, May 2
The Iridium 68 satellite will flare to -6 magnitude around 11:25 p.m. at azimuth 249° (WSW) and altitude 14°, in Hydra.
Saturday, May 3
Saturn resumes direct (eastward) motion relative to the background stars, in Leo near Regulus.
Saturn is closest to Regulus tonight!
Monday, May 5
Eta Aquarid Meteor Shower (7 meteors per hour, or less; nominal peak: 1 p.m.). Radiant rises at 2:39 a.m., transits at 8:37 a.m.
New Moon; rises 5:25 a.m.; transits 1:05 p.m.; sets 9:00 p.m.; 4.1° from the Sun (center-to-center) at 5:56 a.m.; = +21°
Tuesday, May 6
Mercury is near the Moon during early evening twilight. Use binoculars.
Lacrosse 2 (active U.S. spy satellite launched in 1991) will move from NNW to SSE from about 10:25 to 10:30 p.m. It reaches its highest point in the sky (84° altitude, magnitude 2.5) around 10:29 p.m., near Coma Berenices.
The Iridium 72 satellite will flare to -6 magnitude around 11:10 p.m. at azimuth 257° (WSW) and altitude 14°, in Hydra.
Wednesday, May 7
May Librid meteors may be seen around this date.
The Moon sets at its most northerly point along the western horizon this month at 11:32 p.m.
Thursday, May 8
Eta Lyrid meteors (3 meteors per hour, or less). Radiant altitude is 20° at the end of evening twilight; radiant transits at 5:02 a.m.
Meteor showers result from the Earth orbiting through the debris trails of certain comets, and Comet Halley (1P/Halley) has the distinction of being the only comet whose debris produces two meteor showers each year!
The Eta Aquarids of May and the Orionids of October are the two meteor showers, and this Monday morning brings nearly ideal conditions for us to view the Eta Aquarid meteor shower, as it coincides with New Moon. Even though the radiant point, which lies near the Water Jar of Aquarius, is just a smidgen south of the celestial equator ( = -1°), we never see anywhere near the nominal zenithal hourly rate (ZHR) of 70+ meteors per hour because at latitude 43° N the radiant is only 13° above the eastern horizon as morning twilight begins. Maximum rates here in the Wisconsin will do no better than about 7 per hour, just one-tenth the ZHR.
Where is the best place in the world to observe the Eta Aquarids? In other words, at what latitude is the radiant highest above the horizon at the beginning of astronomical twilight? The further south the better--to a point. At the southernmost part of the continental U.S., latitude 25° N in the Florida Keys, the radiant is 31° above the horizon at the beginning of twilight. At the southernmost part of the Hawaiian Islands, latitude 19° N, the radiant is 36° above the horizon at the beginning of twilight. At the southernmost part of Mexico, latitude 15° N, the radiant is 39° above the horizon at the beginning of twilight. But for the best view in the world, you'll want to travel to latitude 13° 4.9' S, where the Eta Aquarid radiant is 48° above the horizon at the beginning of morning twilight. So, the best places in the world to view the Eta Aquarids include Peru, Bolivia, Brazil, Angola, Zambia, Malawi, Mozambique, Madagascar, Northern Australia, and Samoa.
Anyway, if you're in Wisconsin or Iowa or points nearby, the best time to watch for the Eta Aquarids will be Monday, May 5 from about 3:00 to 4:00 a.m. You might even see a few after that, but astronomical twilight begins at 3:54 a.m. and nautical twilight begins at 4:38 a.m. (Dodgeville), by which time the sky will be too bright to see anything but the brightest meteors.
Pierre Kervella, Observatoire de Paris, and six other astronomers recently determined the distance to the Cepheid variable RS Puppis ( = 8h 13m 04s, = -34° 34' 43") using a new and ingenious technique. RS Pup is a long-period (and therefore intrinsically luminous) Cepheid variable with a pulsation period of 41.4 days. Fortuitously, RS Pup is embedded in a reflection nebula. Since the brightness of RS Pup changes, the brightness of the surrounding nebula also changes since it is reflecting the starlight from RS Pup. By measuring the time lag between, say, the maximum brightness of the star and the maximum brightness of a discrete "blob" of nebula, and knowing the speed of light and measuring the angular distance between the star and the blob, a distance to the star can be determined to high precision. How cool is that! Using this technique for ten nebular features, Kervella et al. determined the distance to RS Pup is 6,497 ± 91 ly, a precision of 1.4%.
Of course, this assumes that on average the ten blobs are at the same distance from us as RS Pup, an assumption that has recently been challenged by Michael Feast, University of Cape Town, South Africa.
The absolute visual magnitude of a classical Cepheid variable at maximum brightness is given (approximately) by
where P is the pulsational period in days
Plugging in a value of P = 41.4 for RS Pup, we get Mv = -5.97. The apparent visual magnitude at maximum brightness is 7.009. By making use of the relation Mv = mv + 5 (1-log d), we derive a distance (a "pulsational parallax" if you will) of 3,950 pc, or 12,883 ly. Why is this nearly twice as large as the distance of 6,497 ly derived by Kervella and 5,636 ly and 5,662 - 6,324 ly using other techniques? Answer: we forgot to properly measure and account for interstellar extinction and reddening due to intervening interstellar matter--much of it near the star (remember, the light echoes?). This would cause the star to appear farther away than it really is.
As pristine night skies continue to rapidly disappear from all but the most remote areas in the U.S., thanks to our 24/7 lifestyle and seeming crusade to banish the night, astronomers and other nature enthusiasts are forming special communities with little or no outdoor lighting in places where the night sky is still as it once was everywhere. First there was Arizona Sky Village and Deerlick Astronomy Village in Georgia, and now New Mexico Skies and Rancho Hidalgo in New Mexico, and Sierra la Rana in Texas, are being developed.
All of these small communities have one thing in common: a number of individual acreages rather than a true neighborhood or community. I would like to help create a dark-sky community where the houses, apartments, etc. are clustered relatively close together, where you don't need to own land to be part of the community, and where shared resources and common areas are an integral part of the community. The observing area (with observatories) of the development would be on the southern part of the property, the residential / business part in the middle, and solar panels towards the north end of the property with wind generators north of that. Educational outreach, astrotourism, an onsite telecommuting corporation, and pro-am collaborative research would be important features of the community, as would other elements to broaden the appeal beyond just astronomy.
