As nights grow ever lighter, skies are not sufficiently dark until well after 10pm.
The first ‘stars’ to emerge will probably be the planets, Jupiter, Mars and Saturn, with Mercury also putting on a good show low in the evening twilight. So let us have a closer look as to where to locate them.
Having been so prominent over the last five months or so, conspicuous Jupiter is finally dropping down into the west and is best observed earlier in the month when higher in the sky.
The moon lies nearby on the 4th and again on the 31st.
Having reached opposition early last month, Mars remains a prominent object to the naked eye, residing midway up in the south, upper right of Spica, chief star in Spica.
Through a scope Mars exhibits a small orange disk, with a hint of surface detail – notably the north polar cap. The moon lies nearby on May 10 /11.
Saturn takes centre stage this month, reaching opposition on May10th and is therefore visible from sunset to sunrise. You can locate Saturn over in the southeast during late evening, and due south by midnight, a conspicuous ‘pearly star’ a couple of hands spans left of Mars.
To view the beautiful rings you will need a telescope, any size should suffice, but larger scopes will reveal more detail such as the Cassini and Encke gaps in the rings, as well as subtle surface banding on the disk itself.
Saturn’s largest moon, Titan, which circles around Saturn twice a month, should also be visible as a nearby speck of light. Our moon lies nearby on the 14th.
Mercury bounds back up into the evening twilight sky at the start of May and remains on show until the beginning of June. Look to the WNW 45minutes after sunset around 5 degrees above the horizon (width of a hand at arm’s length). It is highest around the 19th but is brightest before this.
Use binoculars if you cannot initially spot this elusive planet with the naked eye in the bright twilight.
The slim crescent moon lies to the left of Mercury and below Jupiter on the 30th.
Finally, brilliant Venus lingers in the early dawn sky low down in the east before sunrise.
The Eta Aquarid meteor shower peaks on the 6th, but will be best seen on the night of the 5th around midnight. This is one of two meteor showers associated with debris particles deposited over time by comet Halley, the other shower being the Orionids, which peak in late October.
Eta Aquarids have a ZHR (zenith hourly rate) approaching 30, however as Aquarius is only just rising in the SE shortly before dawn, observations from the UK are already restricted. Keep a watch on May 23/24th when a new meteor shower, the 209P-id meteors may occur.
The Celestial Ocean - Twilight and Shadow
As nights become noticeably lighter, now may be a good opportunity to explain why the changes in light levels encountered daily after sunset or before sunrise occur.
If you were to step outside in autumn, winter or early spring, skies are fully darkened by around 9pm.
This deepest level of darkness, known as Astronomical twilight, is just one of three levels experienced, the others being Civil and Nautical twilight respectively.
However, because of our location (latitude) on the surface of the globe, as Earth orbits around the Sun, the duration of twilight levels varies considerably.
So let me explain a little further using evening twilight as an example.
Immediately after sunset Civil twilight exists until the Sun is approximately 6 degrees below the horizon. At this point normal daytime activities that require light cease to be possible and ‘lighting up’ time occurs.
If skies are really clear look out for an interesting phenomena half an hour or so after, and opposite the position of sunset. In this direction a hazy, darkish purple band just above the ESE horizon gradually ‘heaps up’ before being engulfed by deepening twilight.
You might think this is mist, but it is actually the shadow of Earth itself, being cast back into space.
As the Earth spins a little further round and the Sun’s elevation below the horizon reaches approximately 12 degrees, the marine horizon is no longer apparent and Nautical twilight exists.
In the heavens only the brighter navigational stars are visible.
Finally, when the Sun drops approximately 18 degrees below the horizon (a hands span) Astronomical twilight commences and the remaining fainter stars become visible, unless light pollution drowns them out. With the approach of dawn the same lighting levels are experienced - only in reverse.
As we move toward summer the northern hemisphere is inclined towards the Sun and twilight duration’s alter significantly. From the latitude of Whitby astronomical twilight is totally absent for 82 nights; from late May until mid August. The Suns journey beneath the horizon is so shallow it never actually reaches 18 degrees. Matters become worse (for the astronomer) around the summer solstice when even nautical twilight levels barely exist, the Sun setting by a mere dozen degrees.
At least from northern England summer astronomy is just about possible, but as you travel further north nocturnal conditions grow ever lighter and only 13 degrees north of Whitby at latitude 67 degrees N (the Arctic Circle) twilight on any level is completely absent for part of summer and the Sun is visible above the horizon 24 hours a day. Only solar observers are completely happy for in the land of “midnight sun” star gazing is limited to just one, that is if it’s not cloudy.
A Night at the Museum
An evening of visual delights lies in store on Friday May 23 at the Whitby Museum, when top astro lecturer Paul Money will be presenting ‘Images of the Universe vol 5’, the story behind 12 of the most profound, significant and spectacular images ever taken of the our celestial surroundings.
Doors are open from 7pm for a 7.30pm start. Admission is £2.50 for adults and £1 for under 14s. Home-made refreshments will be available.
Paul’s presentations are infotainment of the highest order, so if you fancy ‘a night at the Museum’ please arrive in good time, you will not be disappointed. Lecture is in the Normanby room so please use Chubb Hill entrance. Limited parking is available.
The final Whitby and District Astronomical Society monthly meeting before the summer will be on May 6 at Whitby College, room H1 from 7.30pm.
The WDAS will be hosting the first of our public summer star parties from the Captain Cook statue area on the West Cliff on May 10 and 24 from 9pm. We shall be targeting all the visible planets as well as the moon – weather permitting.
For more information visit www.whitby-astronomers.com or email Spanton33@talk.talk.net