Download (1) Why is the Pleiades star cluster visible all night around

Seasonal Visibility of Stars; and
Planet Visibility in 2013-2014 from
Positions of Planets in their Orbits
-- Robert C. Victor
These orbit charts and accompanying data
table can be used for plotting the positions of
the six inner planets, and determining any
planet’s visibility as seen from Earth. In
addition to doing the problem set below as a
desktop activity, students can “act out” each
problem’s situation in the classroom, by
having one student represent the Sun,
another the Earth, and others the five other
planets.
Be sure to have all students take a turn at
representing the Earth. That student will do
more than just stand in place, but will rotate
as well, to determine planet visibility at dusk,
in middle of night, and at dawn.
These two charts of the orbits of the planets,
one showing Mercury through Mars, and the
other Mercury through Saturn, depict the
view as seen from the north side, or “above”
the solar system. In these views, the direction
of revolution of the planets about the Sun is
counterclockwise. The outer circular scale is
labeled with values of heliocentric longitude,
measured from the Vernal Equinox, or
apparent direction of the Sun as seen from
Earth at the beginning of northern
hemisphere spring. That scale also indicates
the directions of the thirteen zodiacal
constellations (those in the plane of the
Earth’s orbit) from the Sun.
The directions of the five first magnitude
stars Aldebaran, Pollux, Regulus, Spica, and
Antares, as well as the Pleiades star cluster,
are also indicated. The outer circular scale
should be imagined to be much larger than
shown: Earth is one astronomical unit, or 81/3 light minutes from the Sun, compared to
stellar distances of many light-years. One
light-year
is
approximately
63,000
astronomical units. On a chart where the
Sun-Earth distance (one a.u.) would be
represented by one inch, a light year would
be represented by one mile.
On both orbit charts, the Earth’s orbit is
exactly in the plane of the sheet of paper.
For each of the other orbits, the portion
drawn as a solid curve lies north of or above
Earth’s orbit plane. The dotted part of the
orbit lies south of or below Earth’s orbit
plane.
From the north side of the solar system, the
Earth’s rotation on its axis also appears
counterclockwise. But the axis of Earth does
not point at right angles to the plane of the
orbit; rather, it tips away from the
perpendicular, leaning by about
23.4° toward the top of the chart or the 90°
mark on the circular scale.
Using both orbit charts and the data table,
try working out the answers to these
questions:
(1) Why is the Pleiades star cluster
visible all night around November
20? Where (in what direction in the
sky?) would you expect to see it at
nightfall? In the middle of the night?
At dawn’s first light? Why can’t you
see the cluster for several weeks
around May 20?
(2) On what approximate date each
year is Aldebaran visible all night?
Give approximate date of all-night
visibility for Pollux; Regulus; Spica,
Antares.
(3) On what approximate date each
year is Earth heading toward
Antares and away from Aldebaran?
On that date, Antares is visible at
(dusk or dawn?) about 90 degrees
from the Sun, while Aldebaran is
visible at (dusk or dawn?), about 90
degrees from the Sun.
(4) In which month would a Last
Quarter Moon appear near the star
Spica? Hint: The Last Quarter Moon
occurs when the Moon appears 90
degrees or a quarter-circle west
(clockwise in this top view) of the
Sun.
(5) Which constellation is hidden
beyond the Sun for about the first
month of Northern Hemisphere
summer?
(6) At the end of which month in
2013 will Venus reach its greatest
angular separation from the Sun in
the afternoon and evening sky? In
what phase will Venus appear then?
Try to observe it through a telescope
in the daytime around then, and
with telescopes and binoculars in
following weeks.
(7) What alignment involving Sun,
Venus, and Earth will occur on
January 11, 2014? Notice Venus
will be located in the portion of its
orbit plotted as a solid curve, rather
than dotted. At the alignment taking
place on Jan. 11, will Venus pass
north, or south, of the Sun’s disk?
Just over 19 months earlier, on
June 5, 2012, Venus passed directly
in front of the Sun’s disk, causing a
transit of Venus, which won’t
happen again until December 10,
2117. During the weeks leading up
to and following the event on
January 11, 2014, what will be the
phase of Venus?
(8) Which planet will be visible all
night on January 5, 2014? In which
constellation does it appear?
(9) Which planet will be visible all
night on April 8, 2014? In which
constellation does it appear? Which
bright star will appear very close to
the Full Moon on the night of April
14, 2014 with the same planet
nearby? Later that night, there will
be a total eclipse of the Moon, as the
Moon passes through the Earth’s
shadow.
(10) Saturn will be visible all night
just before the middle of what
month in 2014?
(11) Which four planets will be
visible at dusk (soon after sunset)
for most of May 2014? List the four
planets in order of their positions in
the sky, from western horizon to
eastern horizon. As the Earth
rotates, which planet will set first?
Second? Third? Last?
(12) Which two planets will appear
close together in our sky on August
18, 2014? What time of day will they
be seen, at dusk or at dawn?
(13) Which other planets will form a
fairly close pair later that month?
Will the event be seen at dusk or at
dawn?
Robert C. Victor was Staff Astronomer at Abrams
Planetarium, Michigan State University. He is now
retired and enjoys providing sky watching
opportunities for school children in and around
Palm Springs.