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EI2GYB > ASTRO 27.09.21 08:48l 205 Lines 9466 Bytes #999 (0) @ WW
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Subj: This Week's Sky at a Glance, Sept. 24 - Oct. 2
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This Week's Sky at a Glance, Sept. 24 - Oct. 2
Nova Cassiopeiae 2021 carries on, fluctuating unpredictably as it remains in
binocular view six months after its March explosion. As of September 21st it
was back up to magnitude 6.7, more than twice as bright as its original March
eruption from its 15th-magnitude baseline. Charts and comparison stars.
FRIDAY, SEPTEMBER 24
Ý Bright Jupiter and fainter Saturn continue to dominate the southern evening
sky, 16ø apart. All week Jupiter shines just above or upper right of
3rd-magnitude Delta Capricorni, Deneb Algedi (the name means "Tail of the Young
Goat"). The scene is shown below for late twilight this evening.
Farther to the upper right of Saturn, look for Alpha and Beta Capricorni. Both
are binocular double stars. Alpha is a wide pair of yellow-orange giants that
the smallest binoculars easily resolve; so does our chart below. The components
of Beta are half as far apart, much more unequal, and oriented roughly the same
way as the Alpha pair.
Ý Jupiter's Great Red Spot should cross Jupiter's central meridian around 9:04
p.m. Eastern Daylight Time. For full timetables of the Red Spot's transits as
well as the doings of Jupiter's moons and their shadows, see the Celestial
Calendar section of Sky & Telescope magazine.
SATURDAY, SEPTEMBER 25
Ý Cygnus the Swan floats just about straight overhead these evenings. Its
brightest stars form the big Northern Cross. When you face southwest and crane
your head way, way up, the cross appears to stand upright. It's about two fists
at arm's length tall, with Deneb as its top. Or to put it another way, when you
face that direction the Swan appears to be diving straight down.
The waning gibbous Moon doesn't rise now until about an hour after dark. So
take this opportunity to look for the Milky Way running straight up from the
west-southwest horizon, along the backbone of Aquila and just to the right of
bright Altair high in the south; then along the shaft of the Northern Cross
overhead, and straight down through Cassiopeia and northern Perseus to the
east-northeast horizon.
SUNDAY, SEPTEMBER 26
Ý Bright Arcturus, pale yellow-orange, shines ever lower in the west-northwest
at nightfall. The narrow kite shape of its constellation, Bootes, extends two
fists at arm's length to Arcturus's upper right. Arcturus is where the kite's
downward-hanging tail is tied on.
To the right of the top of the kite, the Big Dipper is turning more level.
And this is the time of year when, during the evening, the dim Little Dipper
"dumps water" into the bowl of the Big Dipper way down below. The Big Dipper
will dump it back in the evenings of spring.
Ý Tonight Jupiter's Great Red Spot should cross the planet's central meridian
around 10:42 p.m. EDT (7:42 p.m. Pacific). It remains in good view for about an
hour before and after that time.
MONDAY, SEPTEMBER 27
Ý Arcturus shines in the west in late twilight these evenings. Capella, equally
bright, is just rising in the north-northeast (depending on your latitude; the
farther north you are the higher it will be). They're both magnitude 0.
Later in the evening, Arcturus and Capella shine at equal heights in their
respective compass directions. When will this happen? That depends on both your
latitude and longitude.
When it does, turn around and look low in the south-southeast. There will be
1st-magnitude Fomalhaut at the about same height too - exactly so if you're at
latitude 43ø north (about the latitude of Boston, Buffalo, Milwaukee, Boise,
Eugene). Seen from south of that latitude, Fomalhaut will appear higher than
Capella and Arcturus are. Seen from north of there, it will be lower.
TUESDAY, SEPTEMBER 28
Ý Last-quarter Moon tonight (exact at 9:57 p.m. Eastern Daylight Time). The
Moon rises around 11 or midnight in Gemini, down below Capella and the rest of
Auriga.
An hour later look off to the Moon's right, and there's Orion stepping up over
the eastern horizon (for viewers at mid-northern latitudes).
WEDNESDAY, SEPTEMBER 29
Ý The starry W of Cassiopeia stands high in the northeast after dark. The
right-hand side of the W (the brightest side) is tilted up.
Look at the second segment of the W counting down from the top. Notice the dim
naked-eye stars along that segment (not counting its two ends). The brightest
of these, on the right, is Eta Cassiopeiae, magnitude 3.4. This is a remarkably
Sun-like star just 19 light-years away, and it has a orange-dwarf companion,
magnitude 7.3, separation 13 arcseconds - a lovely binary in a telescope.
Left of it, and fainter, is a naked-eye pair in a dark sky: Upsilon1 and
Upsilon2 Cassiopeiae, a good 0.3ø apart. They're yellow-orange giants unrelated
to each other, 200 and 400 light-years distant from us. Upsilon2 is slightly
the brighter of the pair. It's also the closer one.
Ý Night owl? Look east any time from 1 or 2 a.m. to early dawn Thursday
morning, and you'll find the waning Moon near Pollux in Gemini. Above Pollux is
Castor.
THURSDAY, SEPTEMBER 30
Ý The big asteroid 2 Pallas, almost three weeks past opposition, stands high in
the southeast by 9 or 10 p.m. It's still in small-telescope reach at magnitude
8.4. This week Pallas is 8ø or 9ø upper right of Neptune, magnitude 8.7, which
also is past opposition. Read about both and hunt them down using the finder
charts in Asteroid Pallas Makes a Point in Pisces.
FRIDAY, OCTOBER 1
Ý Vega is the brightest star just west of the zenith after dark. Face west and
look to Vega's right by 14ø (nearly a fist and a half at arm's length) for
Eltanin, the nose of Draco the Dragon. The rest of Draco's fainter,
lozenge-shaped head is a little farther behind. Draco always eyes Vega as they
wheel around the sky.
The main stars of Vega's own constellation, Lyra - faint by comparison - extend
to its left (by 7ø).
Ý Before and during early dawn Saturday morning October 2nd, look below the
crescent Moon by about a fist at arm's length for Regulus, forefoot of Leo
already making his early-apparition appearance, as shown below.
SATURDAY, OCTOBER 2
Ý During evening, look just above the northeast horizon - far below high
Cassiopeia - for bright Capella on the rise. How soon Capella rises, and how
high you'll find it, depends on your latitude. The farther north you are, the
sooner and higher.
Ý Vega is the brightest star very high in the west, and Arcturus is getting low
in the west-northwest. The brightest star in the vast expanse between them,
about a third of the way from Arcturus up toward Vega, is Alphecca, magnitude
2.2 - the crown jewel of dim Corona Borealis. Alphecca is a 17-day eclipsing
binary, but (like most variable stars!) its brightness dips are too slight for
the eye to see reliably.
Ý Before and during early dawn Sunday morning October 3rd, the waning crescent
Moon forms a flat, almost isosceles triangle with Regulus and Algieba (Gamma
Leonis) to Regulus's left or upper left, as shown above (for North America).
This Week's Planet Roundup
Mercury is hidden deep in the glare of the Sun.
Venus, brilliant at magnitude -4.2, shines low in the southwest during
twilight. And it still sets around twilight's end.
Jupiter and Saturn continue to shine in the southeast to south during evening.
They're magnitudes -2.7 and +0.5, respectively, 16ø apart on opposite sides of
dim Capricornus.
During twilight bright Jupiter, on the left, is slightly the lower of the two.
They level out soon after dark, and later they tilt the other way, with Saturn
now the lower one. Saturn sets around 2 a.m. daylight-saving time, followed
down by Jupiter about an hour later.
In the evening look for 1st-magnitude Fomalhaut 23ø (two fists) lower left of
Jupiter. And less than 2ø below or lower left of Jupiter is 3rd-magnitude Delta
Capricorni, described in the caption above.
Also, see Amateurs Spot New Impact Flash at Jupiter. With videos of it taken by
two amateur Jupiter-impact monitors.
Uranus (magnitude 5.7, in southern Aries) climbs high in the east by midnight.
Neptune (magnitude 7.8, at the Aquarius-Pisces border) is high in the southeast
by 9 or 10 p.m.
All descriptions that relate to your horizon - including the words up, down,
right, and left - are written for the world's mid-northern latitudes.
Descriptions that also depend on longitude (mainly Moon positions) are for
North America.
Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is
also known as UT, UTC, GMT, or Z time. To become more expert about time systems
than 99% of the people you'll ever meet, see our compact article Time and the
Amateur Astronomer.
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