Whitby & District Astronomical Society

In this month's Sky Notes:

• Planetary Skylights
• September 2020 Sky Charts

Planetary Skylights

Jupiter and Saturn are better placed for ‘observer friendly’ observations throughout September, however by the end of the month Jupiter’s crown as dominant evening planet will be usurped by Mars.  Neptune comes to opposition this month, whilst Venus reigns supreme in the dawn sky.

As twilight falls you will locate conspicuous Jupiter to the south, with Saturn following a little distance in its wake.  Although both came to opposition a few months ago, they will now be more favourably placed for observation during the evening to the left of the ‘teapot’ asterism in Sagittarius. 

Both are very rewarding to view with smaller instruments, even binoculars are sufficient to reveal the Galilean moons of Jupiter, but not quite the rings of Saturn, you will require a small telescope at least to view them.

Over the course of September Jupiter will fade a tad from Mag -2.4 to -2.2.  Apertures of 100mm (4inch) or above is sufficient to reveal some detail on the banding across Jupiter’s flattened disk, and when orientated towards us the great red spot (GRS), the major storm feature on Jupiter.  By Septembers end Jupiter will be setting by 23:30 BST.

Jupiter GRS and Galilean moon shadow transit visibility- evenings only.  All times BST.

• 1^st GRS visible and Io shad transit from 22:00h.
• 2^nd GRS visible 20:30–21:30h.
• 3^rd GRS visible from 23:30h.
• 4^th GRS 20:30–23:00h.  Europa shadow transit from 22:00h.
• 6^th GRS visible from 21:00h.
• 8^th GRS visible from 23:00h.
• 9^th GRS visible from 20:00h to 22:00h.
• 10^th Io shadow transit 20:00–21:00h.
• 11^th GRS visible from 21:45h.
• 12^th Ganymede shadow transit 20:00–22:30h.
• 13^th GRS visible from 22:00h.
• 14^th GRS visible 19:35–22:15h.
• 16^th GRS visible 21:00–22:45h.
• 17^th Io shadow transit 20:00–22:00h.
• 18^th GRS visible from 21:15h.
• 19^th GRS visible 19:45–20:45h.
• 21^st GRS visible 20:00–22:00h.
• 23^rd GRS visible 20:00–23:00h.
• 24^th Io shadow transit from 22:15h.
• 25^th GRS visible from 22:15h.
• 26^th GRS visible 19:30–21:15h.
• 28^th GRS visible 20:00–23:00h.
• 29^th Europa Shadow transit 19:30–21:00h.
• 30^th GRS visible from 21:00h.

Stick with it, as moments of clarity will reward your patience.  The Moon passes below Jupiter and Saturn on the 1^st and 2^nd respectively and again on the 28^th and 29^th.

Saturn is also now best placed during the evening.  At mag +0.4 it appears considerably fainter than Jupiter, but is still quite prominent to the eye.  The rings remain well orientated with respect to earth, and given moments of good seeing the two main rings; A and B should be evident, separated by the Cassini ‘gap.

Look also for Titan, Saturn’s largest moon, which resembles a bright, but obvious speck nearby Saturn.

Have patience at the eyepiece when viewing Jupiter and Saturn as neither are particularly high above the horizon, with ‘seeing’ thru’ the eyepiece compromised somewhat by the turbulent air.  The Moon passes below Jupiter and Saturn on the 24^th and 25^th respectively.

Mars is already conspicuous to the naked eye in the early morning sky, but rapidly gains in brightness through September as it heads towards opposition in October and by the end of the month will become the dominant presence in the late evening sky.  Look for the distinct orange hue of the planet rising in the east when Jupiter and Saturn lie to the south.  By September 9^th Mars reaches its first stationary point, before starting to move in retrograde motion (east to west) through Pisces.  By the end of September the red planet will have increased in brightness to -2.5, from Magnitude ­-1.8 at the start.

Telescopically Mars is improving through the eyepiece, with the disk size approaching 22.5 arc seconds by the end of the month.  This is still however half the size of Jupiter’s disk, so do not expect to view something as ‘big as a pizza’ despite what some reports on the ‘net may imply.  If there are no obscuring Martian dust storms, you will be gazing at the surface itself; apart from our moon, Mars is the only other body in the solar system where the surface is visible to typical amateur instruments.  Features to look out for are the southern polar cap, Syrtis Major and Hellas Planitia.  The waning moon passes below Mars on the 5^th.

Neptune reaches opposition on the 11^th and resides in the constellation of Aquarius.  On opposition night Neptune lies just over 2 degrees north-east of the star Phi aqr (Mag +4.2), whilst 96 aqr.  (Mag +5.5) lies 42 arc minutes to the WNW of it.  At a distance of 4.3m km (2.67m miles), you will require a telescope to spot the diminutive disk, which has a blue/grey hue.  Binoculars will also show it as a speck – if you know exactly where to look.  A 10” scope or larger should be able to pick out Triton, Neptune’s largest moon.

 

Meteors

None mentioned, this month.

 

Autumnal Equinox

By astronomical convention autumn officially commences in the northern hemisphere on the date of the Autumnal Equinox, when from our perspective the Sun re-crosses the celestial equator and heads south, arcing ever lower above the south horizon.  This year the date of the equinox falls on September 22^nd. 

For the second time in its orbit around the Sun, neither of Earths poles is inclined towards our nearest star with hours of daylight and darkness almost equal across the whole planet.  As the northern hemisphere continues to tilt away from the Sun, evenings will rapidly draw in once again as we head toward winter.  Cheery thought!

 

September 2020 Sky Charts

Looking North Mid-September - 21:00h	Looking South Mid-September - 21:00h
Looking East Mid-September - 21:00h	Looking West Mid-September - 21:00h
Northern Aspect Mid-September - 21:00h	Southern Aspect Mid-September - 21:00h
Northern Aspect (Early) Mid-September - 05:30h	Southern Aspect (Early) Mid-September - 05:30h

 

Additional Image Credits:

• Planets and Comets where not otherwise mentioned: NASA
• Sky Charts: Stellarium Software