What’s in the Sky in September

/in /by

September

 

The best time to observe the dust orbiting Earth, which is known as the Zodiacal Light, is around the Southward Equinox which falls this year on 23rd September  AEST.
So a couple of days either side you can look for it.
You do need a dark sky to see the zodiacal light so head to the darkest sky you can reach and look just after sunset. Turn off unnecessary lighting to help keep the night dark.
  • 1st Saturn is just past Opposition ( closest position to Earth, which was on 27th August and is a stunning evening object at Magnitude o.4, distance 1309.9 million km, 72.82 light minutes away.
  • 13th  Moon at Apogee, furthest point from Earth this month, 01:43hrs AEST,  distance from Earth 402,292.4 km.
  • 23rd Southward Equinox 16:50:25hrs AEST.
  • 23rd 7.00pm AEST magnitude 5.1 Comet Nishimura a very faint object near Mars, 5 degrees above the horizon. The comet is moving away from Earth, towards behind the Sun.
  • 28th Moon at Perigee, Closest point to Earth this month, 11:01hrs AEST, distance from Earth 359,914.3km.

 

 

  • Universal Nomenclature of the      Equinoxes and Solstices Each celestial object has coordinates similar to a street directory to locate its’ position in the heavens.Celestial Sphere – An imaginary sphere surrounding the Earth on which the celestial bodies appear to lie.Celestial Longitude (CLong) – coordinateon the Celestial Sphere that corresponds tothe longitude on Earth and is measuredfrom 00.00h. Measured in hours, minutes, seconds or sometimes given as degrees,minutes seconds corresponding to degrees

    in a circle, ie 360 degrees.

     

    Celestial Latitude (CLat)– corresponds to latitude on Earth’s surface and is measured

    in degrees, minutes, seconds. Up to 90

    degrees North (Nth) or South (Sth) of the Celestial Equator.

    + for the Northern Hemisphere,

    – for the Southern Hemisphere.

     

    Celestial Equator – directly above the

    Equator on the Earth’s surface.

     

    Northward Equinox – Day & Time the

    Sun crosses the Celestial Equator travelling into the northern Hemisphere. 00.00h CLong

     

    North Solstice   – Date and Time Sun reaches its’ furthest northern position ~ 23.5 degrees Nth. of the Celestial Equator. The Tropic of

    Cancer on the Earth’s surface, northern limit

    of Sun overhead.

                       

    Southward Equinox – Day and Time

    Sun crosses the Celestial Equator travelling into the Southern Hemisphere.

     

    South Solstice – Date and Time the Sun

    reaches its furthest s outhern position ~ 23.5 degrees Sth. of the Celestial Equator.

    The Tropic of Capricorn on the Earth’s

    Surface, southern limit of Sun overhead.

     

    The preceeding 4 terms indicate:

    1.Direction of the Earth’s Poles

    relative to the Sun.

    2.Extent of the Nth/Sth movement

    of the Sun overhead

    3.Direction of seasonal change of the

    position of the Sun due to the angle of the

    Earth’s axis of rotation,  ~ 23.5  degrees.

    Ecliptic – Path of the Sun against the background of the stars.

     SCP – South Celestial Pole

    NCP -North Celestial Pole

    Both directly above the Earth’s Poles.

     

    The Point of Northward Precession –

     The point the Sun crosses  the Celestial Equator travelling  into the Northern Hemisphere. The point is actually moving 1/7 sec/day. It is linked  to Celestial Longitude as the point slowly  slips along the Celestial Equator.

     

    Epoch   For a printed map the stars positions are fixed and so the Epoch date needs to be stated, ie Current Epoch is 2000.  Printed star maps are good for about 50 years, then the next epoch data is required for astronomers, ie next epoch will be 2050.

     

    Tropical Year – Time for the Sun to travel from one Northward Equinox to next,

    365.2422 days.

     

    Siderial Year – Time taken for the Earth to complete one orbit relative to the fixed stars, 365.2564 days.

     

    The difference between the Tropical and Siderial years is due to the effects of

    precession, a gradual westward drift in the ecliptic. The gravitational pull of the Sun and Moon on the Earth’s equatorial bulge cause

    the Earth’s axis to trace out  a circle on the sky every 25,800yrs.

     

    Judith Bailey – Ballarat Municipal Observatory & Museum

    E:  info@ballaratobservatory.org.au 0429 199 312

     

    First printed 18.3.2010 Updated 20/7/2022

  • 27th  Jupiter is at opposition and closest for 59 years. Viewing available at the Observatory Book Online
  • 2nd Oct Daylight Savings begins. AEDT Time.