The night sky in September 2015

posted 27 Aug 2015, 12:33 by Pete Collins
by Anne Holt

Sunset:   Sept 1st   19.59,   Sept 30th   18.48

Sunset on 24th, the day of our first meeting of the season,  is at 19.03

The Autumnal Equinox, when the sun crosses the celestial equator, is on 23rd.

This month's highlight


The big event this month is, of course, the total Lunar eclipse in the early hours of Monday 28th. The Moon will move into the Earth's shadow at 02.07 BST. Totality is from 03.11 to 04.28.  During totality the moon can be seen as sunlight passing through our atmosphere is refracted onto the surface as it hits water and dust particles.The green to violet part of the spectrum is filtered out leaving the red and orange rays to fall on the moon.  The colour of the eclipsed moon can range from a copper hue to a deep blood red, depending on atmospheric conditions at the time.

September's full moon is the Harvest Moon (nearest full moon to the autumnal equinox) and the largest this year, as it is at its closest to Earth, so this eclipse could be really spectacular - weather permitting.

Constellations

The Milky Way in still prominent overhead, albeit not in these parts! Find a dark sky site though, and it's spectacular.

The Summer Triangle is high in the southern sky for much of the night in early September.  By month end Aquila is setting in the west at about 2am, with Lyra and Cygnus following just before dawn.

However, on the opposite side of the sky, the Pleiades are climbing above the horizon in the east by 10.30pm at the start of September, and as darkness falls at month end. Capella, in Auriga, and the V shaped Hyades cluster at the head of Taurus the Bull are not far behind.

If you stay up until about 4am (or get up very early) you might see Orion making a welcome return to the night sky.  By the end of September, it should be above the horizon by 2am.

The ecliptic is now slightly higher across the Eastern sky, passing through Capricorn, Aquarius and Aries - though none of these are particularly bright or memorable.

Pegasus, Perseus and Andromeda are still well placed, rising in the east to north east from mid evening, as is the bright W asterism of Cassiopeia higher in the north east.


Planets

Several planets are now morning objects, so may be seen by anyone getting up early, or staying up late, to view the eclipse.

Venus:  at mag -4.4 is now shining very brightly in the dawn sky.  At the start of September it will be rising about 90 minutes before the sun, increasing to almost 4 hours by month end.

Mars, in Cancer, is moving into Leo during the month, mag 1.8. It's not far from Venus but around 300 times  fainter. It will be less than one dgree from the bright star Regulus in Leo on the morning of 25th.

Jupiter: also in Leo,  mag -1.7. In early September it may be visible low in the South East, just before sunrise.  By month end it will be rising around 4.30.

Uranus:  in Pisces, mag 5.7. Rising around 9pm in early Sept and as the sky darkens by the end of the month, visible for most of the night. It's a good test of eyesight and viewing conditions.  If you can see it with the naked eye, both are excellent.   It is easily seen in good binoculars but the greenish colour can only be seen through a telescope. it will be just one and a half degrees south of the Moon at 3am on 29th.

Neptune:  in  Aquarius, mag 7. At opposition on Sept 1st and visible, fairly low in the sky, all night long - through a telescope. You need a good finder chart or goto telescope to locate it.

Saturn: in Libra, mag 0.6. Setting not long after the sun but may be visible, low in the South West, as the sky darkens,  especially in the early part of the month.

Mercury: reaches greatest eastern elongation on 4th but is still very low on the Western horizon and hardly visible.

Comet 67P Churyumov Gerasimenko (the comet that the Rosetta probe is following) might be visible in larger scopes this month. It is expected to be at around mag 13 in early September. It starts the month in Gemini then moves down through Cancer, passing close to M44 around 15th to 18th, then into Leo at month end.
For more info see theskylive.com/67p-info
This site also gives charts of the positions of many other celestial objects.

Meteor Showers

No major showers, though sporadic activity is said to be high in September.

Alpha Aurigids
Active until Sept 10th.  Peak August 31st but some meteors could still be seen.

September Perseids,
Active 5th to 21st.  Peak 9th  ZHR 9
Usually faint meteors.   There was a stronger display in 2013, so you never know!

Beta Cassiopeids
Couldn't find much information about these, except that they peak between Sept 1st and 6th.

Piscids
Descriibed  as weak and diffuse, possibly has 2 separate radiants.  It also appears to have 2 peaks - 9th and 21st of September.
One site says that this shower is 'poorly observed due to lack of observation'.   Can't argue with that.  
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