Norfolk Astronomical Society
Astronomical Trivia 2004
The Astronomy Trivia Quiz is a monthly feature of Norfolk Skies, The Official Newsletter of the Norfolk Astronomical Society.
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Q: What type of astronomical object is prefixed by "LGM" numbers, and what does that prefix stand for?
A: When radio noise from the first pulsars were detected, radio astronomers initially thought the regularity of the signals might be an indication of life elsewhere (Little Green Men) in the universe, thus the LGM prefix for this type of object. You can read the story on The Planetary Society web site at
http://www.planetary.org/html/UPDATES/seti/SETI@home/Update_010902.htm
Congratulations go to Chris O'Brien of Richmond, VA for being the first to come up with the answer. Chris is in the Army expects to be stationed near our area at Fort Eustis from July to October of this year.
Q: What is the name given to the bright areas seen on the surface of our sun, often seen surrounding sun spots?
A: Faculae is the correct answer. The Facts On File Dictionary of Astronomy defines "faculae" as:
"Bright patches in the upper part of the upper part of the solar photosphere (sun's visible surface) that have a higher temperature than their surroundings and occur in areas where there is an enhancement of the relatively weak vertical magnetic field. With the exception of polar faculae, which consist of isolated granules and appear in high heliographic latitudes around the minimum of the sunspot cycle, they are intimately related to sunspots: they form shortly before the spots - in the same vicinity - and persist for several weeks after their disappearance. Faculae are best seen when near the sun's limb, where limb darkening renders them more readily visible. They are approximately coincident, albeit at a lower level with the plages visible in monochromatic light."
Congratulations go to Ron Robisch for being the first to
correctly answer, and to Kent Blackwell for his further explanation
that faculae is derived from Latin and means "little torches".
Q: At Summer Solstice, when the sun is at its most northerly
declination in the sky, which city has the longest period of daylight
(sunrise to sunset): New York City, NY or Chesapeake, VA? How
does this differ at Winter Solstice? Why?
A: At the Summer Solstice, when the sun reaches its most northerly
declination, the further north you go in latitude, the longer
your day. This should also be true anytime the sun is at northerly
declinations. Finally, if you travel far enough north and enter
the Artic Circle, the "Land of the Midnight Sun", the
sun never sets. Conversely, at Winter Solstice (and whenever the
sun is at southerly declinations), the Antartic becomes the "Land
of the Midnight Sun" while the Artic receives darkess for
the entire day.
Thus the answer is that more northerly New York, NY has a longer
period of daylight than Chesapeake, VA at the Summer Solstice,
while the opposite is true at Winter Solstice. The table below
calculated with Astronomy Lab 2.02 clearly shows the difference
in daylight periods.
Q: Why is a magnitude +1 star 2.5 times brighter than a magnitude +2 star?
A: The Greek Mathematician Hipparchus designed a magnitude scheme where the brightest stars of +1 magnitude were 100 times brighter the +6 magnitude stars that were just visible to the naked eye. With a 5 magnitude difference, the difference between magnitudes is the 5th root of 100 or 2.511886.
Q: Brighter stars in the constellations often know by their
proper names. Many of the principal stars are give lower-case
Greek alphabet letters, with "a", or alpha being the
brightest, "b" being beta being 2nd brightest, gamma
being 3rd, etc. What is the name of the individual who came up
with the Greek alphabet labeling system?
A: It was Johann Bayer who published his Uranometria (before Perrry
Remakalus) in 1603. Bob Jones was the first to answer correctly.
Q: In 1780, when thousands of stars became visible in telescopes, the Greek letters of star brightness's proved insufficient.
1. What were these numbers called?
2. Who numbered them?
3. In what order do the numbers appear in each constellation,
i.e., in order of brightness, size, etc?
A: These numbers are called Flamsteed Numbers, but contrary
to popular belief, English astronomer John Flamsteed actually
wasn't the one who numbered them. They are numbered by constellation
in order of right ascension. Flamsteed's original Atlas Coelestis
used Bayer Greek letters for the stars. It was in a 1780's French
edition that French astronomer Joseph Jerome de Lalande first
assigned numbers to the stars. Shared congratulations go to Cliff
Hedgepeth and Glen Howell for being the first to provide portions
of the correct answer.
Q: The 5° 9' inclination of the Moon's orbit to the Ecliptic (the path of the Sun among the stars) causes the Moon to miss eclipsing the Sun, and miss passing through the Earth's shadow most times. What effect does inclination have on the visibility of Solar and Lunar Eclipses, and on stellar occultations as well? What effect would an inclination of 0° have?
Answer: If the Moon's orbit had no inclination it would
move along the Ecliptic just like the Sun does. In reality, the
Ecliptic (path of the Sun among the constellations) represents
the plane of Earth's orbit around our star. A solar eclipse would
occur at every New Moon, and a lunar eclipse at every Full Moon.
All eclipses would be central, meaning that the centers of the
Sun, Moon, and Earth would all fall in line. As such, total solar
eclipses could only occur where the sun can reach the zenith (within
the tropics), whereas the lunar eclipse would be visible to all
who happened to be on Earth's night side as the Moon passed through
earth's shadow.
Because the Moon's orbital inclination, the Moon crosses the Ecliptic
at 2 points in the sky called "Nodes". These nodes are
180° apart. The Moon is at its "Ascending Node"
when moving from south to north of the ecliptic, and at its "Descending
Node" when moving from north to south. These nodes are not
stationary but move 19.34° westward along the Ecliptic each
year, completing a full circuit it 18.61 years. Being 180°
apart, it takes the Sun roughly 6 months to move from 1 node to
the other, whereas it only takes the Moon just over 14 days.
It is the proximity of the Sun to one of the Nodes that determines
when eclipses can occur. Only when the Sun is within the "Nodal
Limits" can the Moon's disk overlap with the Sun's for a
solar eclipse, and since the Earth's shadow is always opposite
the Sun, the Earth's shadow is simultaneously near the other node
where the Full Moon can pass through it for a lunar eclipse. The
nodal limits for each eclipse type is given in the table below:
Nodal Limits Minor Major
Solar Eclipse 15° 21' 18° 30'
Lunar Eclipse 9° 30' 12° 15'
An eclipse will always occur if the Moon (phase of New or
Full) catches the Sun within the "minor" nodal limits.
Under certain circumstances, eclipses may occur with the Sun all
of the way out to the "major" nodal limits. Beyond the
nodal limits, the Moon's shadow passes north or south over the
Earth, or in the case of a lunar eclipse, the Moon passes north
or south of Earth's shadow. Thus solar eclipses that occur out
close to the nodal limits occur near Earth's poles, where those
where the Sun is very near the node itself occur near the tropics.
Indeed, eclipse series always begin at one pole with each successive
series member occuring closer to the equator, with the series
ending at the opposite pole of Earth.
The 19.34° per year westward movement of the nodes along the
Ecliptic has the effect of closing the distance the Sun must traverse
to get back to the node, so eclipses occur earlier each year.
The westward movement of the nodes when combined with the 5°
9' inclination of the Moon's orbit, also means that all stars
within 6° or so of the Ecliptic can be occulted by the Moon,
with these also repeating in cycles related to the 18.61 year
period.
Q: On your 57th birthday, while observing, you note the
phase of the Moon is Last Quarter. From this information, what
was the phase of the Moon on the date of your birth? What cycle
tell you this is true?
A: Every 19 years, the phases of the Moon repeat on the same date
in a cycle called the "Metonic Cycle", named after the
Greek Astronomer Meton who discovered it in the 5th Century BC.
In this case, three (3) cycles of 19 years equals 57 years. Cliff
Hedgepeth was the first to answer correctly.
As it turns out, 19 years is also almost equal to 20 eclipse years.
This means that an eclipse may or may not be repeated on the same
date 19 years later. For instance, a solar eclipse will occur
on April 8, 2005. Nineteen (19) years later, on April 8, 2024,
there will be yet another solar eclipse.
Q: Geosynchronous satellites (GEOSATS) are launched into
a 22,000 mile high Equatorial orbit where they orbit the Earth
in 24 hours. From our latitude of 37 North, where do these satellites
appear in our sky?
A: As seen by an observer on Earth's equator, GEOSATS would appear
to lie along the Celestial Equator (Declination of 0). Due to
the effect of parallax, however, for an observer at our latitude
of 37 North, the satellites appear in our sky shifted south about
5.9 and thus form a belt across our sky at declination -5.9. Congratulations
go to Bob Jones for coming up with the correct answer.
Q: What month(s) or season(s), and time(s) of night is best to
observe GEOSATS? When would they be brightest and dimmest?
A: Remember that all artificial satellites of the Earth are really
just "artificial moons". Just as the Full Moon is our
satellite's brightest phase, so too are GEOSATS at their brightest
when their surfaces are fully illuminated. Our Moon receives Full
illumination when it is opposite the sun. Ignoring surface irregularities,
so too should GEOSATS be brightest when opposite the sun.
Earth's shadow moves along the Ecliptic opposite our Sun. Around
the Equinoxes in March and September, just as the Sun crosses
the Celestial Equator, so does Earth's shadow. As the GEOSATs
also lie along the Equator, they spend a part of each day in shadow
near the Equinox dates. Thus the best time to observe them around
the Solstices when they pass above or below the shadow.
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