SKY REPORTER: Now You See It, Now You Don’t

Comet ISON C/2012 S1, Hubble image from October 9, 2013
NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Friday October 18th with my first cup of morning coffee in hand, I heard a radio announcer report the sky was expected to be clear that evening so we could see a lunar eclipse. For a second I thought: that’s nice astronomy’s getting media attention; but then--whoa, see the eclipse? Yes, a penumbral lunar eclipse would occur for a while after sunset that evening, however, like all penumbral eclipses, it would be impossible for anyone casually looking up to see any darkening of the Full Moon’s face. Even with binoculars, it would be extremely difficult to see any hint of Earth’s shadow on the lunar disk because, unlike the situation during total or partial eclipses, no section of the moon is completely hidden from direct sunlight during penumbral events.

At the 7:50 p.m. time of maximum eclipse, our son Eric applied his excellent 20/15 vision to try and distinguish which part of the moon appeared darkened. With unaided eyes he saw no suggestion of a shadow. Even with 7x50 binoculars, it took a while before he could correctly note that the lower right of the lunar surface seemed ever so slightly shaded compared to the un-eclipsed upper left.

With this example of inflated expectations in mind, we turn attention to the long anticipated arrival of ISON (C/2012 S1), erstwhile “Comet of the Century.” It recently crossed Earth’s orbit en route to its November 28 perihelion passage, but according to predictions by the International Astronomical Union’s Minor Planet Center, the comet won’t be visible to unaided eyes until about mid-November. Even then, very dark sky probably will be needed in order to catch a glimpse. As ISON accelerates toward the Sun, it continues to brighten, but still might not be seen by urban observers without optical aid until just days before its closest approach to the Sun on Thanksgiving night. Maximum brightness is predicted to be about -4.5, similar to that of Venus but washed out by the Sun’s glare. That peak is expected to be brief, and by sunrise November 29th, ISON will be only a few degrees from the Sun (if it survives perihelion passage). Even if a greatly extended tail should develop, the tail probably will have slight contrast with the twilight sky. However, let’s hope for the best, comets can present big surprises. Perhaps the Sun will provoke emergence of spectacular tails that might extend far into darker skies. We’ll post updates on ISON as it progresses in its fall toward the Sun.

The Moon

A rare combination annular and total solar eclipse occurs early on Sunday November 3rd, the morning we return to standard time by setting clocks back one hour. However, only the last portion of the partial phase is visible from the United States and that ends soon after 6:29 a.m. sunrise in New York City. Remember never look at the Sun directly! Use a safe method such as pinhole projection onto a screen.

November’s Full Moon is November 17th with its traditional names including Full Beaver Moon and Full Frosty Moon. This year it’s located among stars of Taurus.

Planets

The early evening of Wednesday November 6th, the crescent moon appears to the upper right of Venus. On the night of the Thursday November 21-22, a bright waning gibbous moon is about five degrees south of Jupiter. Mars will be just above the waning lunar crescent about 6 am, the morning of Wednesday November 27th.