Saturday: Tonight is International Observe the Moon Night (IOMN). Although you don’t have to wait until night to observe it. The moon rises above the southeastern horizon at 4:00 p.m. By 9:00 p.m., it is one and a half fists held upright and at arm’s length above due south. You’ll see that it is in the constellation Sagittarius. Being “in” a constellation means the object is lined up with the constellation in the sky. The moon sets a little before midnight, marking the end of IOMN. For more information about observing the moon, go to https://science.nasa.gov/moon/observe-the-moon-night/. Or better yet, just go outside between 4:00 p.m. and midnight and observe the moon.
Sunday: To the people of Ancient Greece, the stars that are
about five and a half fists above the northeastern and eastern horizons,
respectively, at 10:30 p.m. were known as Cassiopeia and Andromeda, a
mythological queen and her daughter. But not all cultures imagined the same
pictures in the sky. To the people of Polynesia, the stars of Cassiopeia and
Andromeda represented a dolphin, called Kwu. Cassiopeia formed its tail, the
brightest stars of Andromeda formed its fins, and its fainter stars outlined
the dolphin’s body.
Monday: Saturn is about three fists above the southeastern
horizon at 11:00 p.m.
Tuesday: At 5:00 p.m. PDT, the center of the Sun crosses the
celestial equator and passes into the southern sky. The celestial equator is an
imaginary line that divides the sky into a northern and southern half. When the
Sun is in the southern half of the sky, it appears to take a shorter path from
rising to setting. It also does not get as high in the sky at noon. This leads
to shorter days and longer nights. Since the Sun crosses the celestial equator
today, there is an instant when it is equally in the northern and southern sky,
called the north and south celestial hemispheres. This so-called “equal night”
is given by the Latin word equinox. Thus, today is known as the Autumnal
Equinox. However, the day and night are not of equal duration today. The sun
rises at 6:49 a.m. and sets at 6:58 p.m. in the northern latitudes of the
United States.
Wednesday: Venus is at its brightest of the year this week.
It is lost in the glare of the Sun, just above the southwestern horizon. You
may be able to spot it with binoculars. At 7:00 p.m., pan your binoculars along
the horizon from the position of the recently set Sun to the left towards
southwest.
Thursday: Jupiter is three fists above the eastern horizon
at 6:00 a.m. Mars is about two fists to the upper right of Jupiter, nearly five
fists above the eastern horizon.
Friday: Ask someone which day in September has the same
duration day and night. Go ahead, ask someone. Why are you still reading this?
I’ll wait. If that person says the first day of autumn, they are wrong. Today,
three days after the first day of autumn, is the date on which day and night
are closest in duration. There are two main reasons for this. First, the
atmosphere acts like a lens, bending light from the Sun above the horizon when
the Sun is actually below the horizon. This makes the Sun appear to rise before
it actually rises and appear to set after it actually sets. Second, fall starts
when the center of the Sun passes through the point called the autumnal
equinox. But the Sun is not a point. The upper edge of the Sun rises about a
minute before the center of the Sun, and the lower edge sets a minute after the
center of the Sun. Thus, even if we didn’t have an atmosphere that bends the
sunlight, daytime on the first day of autumn would still be longer than 12
hours.
The positional information in this column about stars and
planets is typically accurate for the entire week. For up-to-date information
about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.
All times are Pacific Time unless noted.
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