Saturday: Saturn is two and a half fists held upright and at arm’s length above due south at 9:30 p.m. At this time, Mars is just rising above the east-northeastern horizon.
Sunday: Ask someone which day in September has the same
duration day and night. Go ahead, ask someone. Why are you still reading this?
I can 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 in 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.
Monday: Jupiter is in opposition tonight. That doesn’t mean
that Jupiter is a teenager. Opposition means that Jupiter is on the opposite
side of the Earth as the Sun. When an object is in opposition, it is at its
highest point in the sky during the darkest time of the day. Thus, opposition
is typically the best time to observe a planet. Jupiter is four fists above due
south at 1 a.m., midnight non-daylight savings time. If you don’t want to stay
up so late, you can see it three fists above due southeast horizon at 9:30 p.m.
Tuesday: To the people of Ancient Greece, the stars that are
about five and a half fists above the northeastern and eastern horizons,
respectively, at 10:00 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.
Wednesday: You discovered Cassiopeia last night. The
astronomer Caroline Herschel discovered an open star cluster that looks like a rose
over 200 years ago. This cluster, called Caroline’s Rose, is about 6,500 light
years away and consists of about 1,000 stars that are one third the age of the
Sun. Through binoculars, it looks like a fuzzy patch. At 10:00 p.m., find the
star at the top of the sideways “W” known as Cassiopeia. When that star is in
the lower left portion of your field of view, Caroline’s Rose is in the center
to upper right. For more information about Caroline’s Rose, go to http://tiny.cc/i0zxsz and have the story read
to you.
Thursday: Mnemonics are helpful for remembering astronomy
facts. (Similarly, “Johnny Mnemonic”, the 1995 cyberpunk film, was helpful in
getting Keanu Reeves’ career going.) After all, school children around the
world are learning the order of the planets by remembering, “My very excellent
mother just served us nine….” Oops, I guess that one needs updating. Well,
here’s one that will not need updating for tens of thousands of years: the
order of the stars in the Big Dipper. Because the nighttime stars are so far
away from us, their actual motion through the sky, called their “proper motion”
is not noticeable over even thousands of years. That is why the constellations
have remained the same since ancient times. But two stars in the Big Dipper
have a proper motion large enough such that in 100,000 years; the stars will no
longer make a dipper shape. You can see this simulation at the American Museum
of Natural History video found at https://youtu.be/sBfUBtdo8yo.
Until then, you can remember the names of the seven dipper stars in order from
handle to cup by remembering this helpful advice for teens: “AM, ask mom. PM,
dad”. The stars are Alkaid, Mizar, Alioth, Megrez, Phad, Merek, and Duhbe. The
Big Dipper is one fist held upright and at arm’s length above the northern
horizon at 11:00 p.m.
Friday: “There’s water in them thar craters”, frozen water,
that is. There has been speculation since the 1960s and indirect evidence since
the 2000s of water on the Moon. Three years ago, astronomers studied data from
four earlier missions. They noticed that the light reflecting off the
bottom of craters near the lunar South Pole showed characteristics of light
reflecting off pure ice. The water likely came from comet impacts or other
solar system objects with trace amounts of water ice. Last week, NASA announced
the landing site for its new Volatiles Investigating Polar Explorer Rover or
VIPER, the mission that will take a close-up view of Nobile crater near the
Moon’s South Pole. For more information about the upcoming mission, watch the
video at https://youtu.be/bd7ekqMrHkg.
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.
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