PDA

View Full Version : Major error in February 2019 Sky and Telescope



Hornblower
2019-Jan-08, 12:18 AM
On p. 49 in the article "Echoes from a Variable Star" the author asserts that RS Puppis, a Cepheid variable, culminates at different altitudes on different dates over a few weeks during the winter, over a range of a few degrees. We all know that the declination of a star, and thus its altitude at culmination, is virtually constant over such a short time, with only vanishingly small changes from precession and proper motion. Unless I am missing something, this is a ghastly error. I have written to them, saying just what I am saying here.

Hornblower
2019-Jan-14, 02:11 PM
On p. 49 in the article "Echoes from a Variable Star" the author asserts that RS Puppis, a Cepheid variable, culminates at different altitudes on different dates over a few weeks during the winter, over a range of a few degrees. We all know that the declination of a star, and thus its altitude at culmination, is virtually constant over such a short time, with only vanishingly small changes from precession and proper motion. Unless I am missing something, this is a ghastly error. I have written to them, saying just what I am saying here.
Another one for the “Oops”! file. In a December 2017 article about the Geminids the author asserted that the meteors are relatively slow because of the shallow angle of entering the atmosphere. As I understand it that is not why they are slow. They are in a direct orbit and are converging at a somewhat low relative velocity. In contrast the Leonids, in a retrograde orbit, meet the Earth in nearly head-on collisions and thus are extremely fast. This holds regardless of whether the entry is grazing when the radiant is at the horizon or nearly vertical when the radiant is high.

grant hutchison
2019-Jan-14, 02:19 PM
Yeah, that makes no sense - the angle should be everywhere from grazing to vertical for all meteor showers, according to whether the meteors strike the edge or centre of the Earth's disc. (From an Earth observer's point of view, depending on whether the radiant is on the horizon or overhead.) What's strikingly different, as you say, is the relative velocity of different showers.

Grant Hutchison