Friday, October 17, 2008

Manitoba Skies - October 2008

This month:
  • Celestial Treats for Hallowe’en
  • Venus at sunset
  • Jupiter low in the south
  • The Hunter’s Moon
NOTE: This is NOT an exhaustive list of what’s going on in the sky! You can also pick up Sky News magazine or consult The Observer’s Handbook 2008, available from the Royal Astronomical Society of Canada.

Celestial Treats for Hallowe’en
Best seen: Hallowe’en night (October 31st), 6PM to 7:30PM

Hallowe’en night brings people outside and under the evening sky, so we’ve prepared a list of Hallowe’en “treats” for you to watch for.

The highlight is in the western sky after dark. Brilliant Venus shines like a white beacon low in the sky, becoming visible as soon as the sun sets (about 6:05 PM for Winnipeg). Below it is a thin crescent Moon. The moon’s “dark” part will be dimly visible as well – a phenomenon called earthshine, since it is light reflected from the earths that is lighting up the “dark” side of the moon. These objects are quite low, so you’ll need a clear horizon to the southwest to be able to see them. If your house has a clear line of sight and you have a telescope or binoculars, invite all the trick-or-treaters to take a look too! Even through common binoculars, the view will be amazing.

Higher up and to the south is the planet Jupiter. It is also an impressive sight for trick-or-treaters, but a telescope is needed to do it justice.

At 7:15PM CDT for areas in and around the city of Winnipeg, stop what you’re doing and look up into the southern sky. Halfway up the sky, you suddenly see a bright “star” appear out of nowhere. It will brighten to outshine everything else in the sky, and then fade away into oblivion. This isn’t a real exploding star – it’s called an Iridium flare. The Iridium series of satellites orbit the earth, carrying communications signals around the globe. As they orbit, sunlight glints off of their shiny solar panels – much like sunlight can reflects off of a moving car’s windows if the angles are just right. The “glint” becomes visible to us on the ground as a slowly moving flare that last a few seconds and then disappears. Iridium flares can be predicted in advance by visiting the web page Select your location from the database and it will tell you when to watch for Iridium flares and other satellite passes, including the International Space Station. (Alas, no ISS passes on Hallowe’en night for us… you’d have to get up early the next morning to see it!)

Venus at sunset
Best seen: evening twilight, all month (special events Oct 1st & 31st)

The brightest object in the sky other than the Sun and Moon, Venus blazes in the southwest after sunset. It becomes visible as the “first star I see tonight”, long before the sky is dark enough to see any other stars. Venus is so bright for two reasons: it is relatively close to us compared to other planets; and it is covered with shiny white clouds which reflect a lot of sunlight at us. Venus is so bright that it is often mistaken for an unnatural object by people unfamiliar with the sky.

On October 1st and again on October 31st, the thin crescent moon joins the scene, as related in our Hallowe’en special report above.

By month’s end, Venus is only a little higher than it was at the beginning of the month, but it has moved farther to the left from our point of view. For the next several months, Venus will be low in the west and southwest as the sun sets.

Jupiter low in the south
Best seen: evening sky, all month

The giant planet Jupiter is still the highlight of the evening sky, despite being so low in the south. Jupiter is now setting about 10PM in the southwest, as the sun catches up to it from our point of view. In fact, it’s the Earth and Jupiter doing the moving. As our planet orbits the Sun, we are swinging onto the far side from Jupiter with the sun moving in between us. Jupiter’s motion also contributes to this, although it is much slower than Earth’s.

Despite the low altitude, Jupiter is still worth a look. Binoculars will reveal some of its moons, which appear as tiny “stars” lined up on either side of the planet. A telescope will reveal some of the cloud bands and perhaps the Great Red Spot, but the telescopic views are affected by Jupiter’s low altitude and so might not be as clear as in previous years. Don’t worry, Jupiter is back every 13 months or so, and the next several oppositions will put Jupiter higher in our sky.

The Hunter’s Moon
Best seen: October 14th all night

The full Moon in October is traditionally referred to as the Hunter’s Moon. Many people believe that this moon, and last month’s Harvest Moon, are bigger and orange in the fall. In fact, the full Moon can appear big any time it is seen rising – this is a well-known but little-understood optical illusion. The orange colour comes from seeing an object through the thicker air near the horizon – the same reason the sun appears red or orange as it rises and sets.

However, the Harvest Moon and Hunter’s Moon are special – they happen to rise at a time when people are heading home, and so they are more often seen and remembered. And of course, in October the Manitoba skies are often shrouded with smoke from farmers burning stubble, and the smoke can enhance the orange colour as the moon rises.

If it’s cloudy on the 14th, don’t worry – most people can’t tell a truly “Full” moon from one that is a day before or after. You’ll have several nights around the 14th to watch a big orange moon rise into the prairie night!

The Planets as seen from Manitoba:

Mercury becomes a dawn object in the second half of October, appearing as a fairly bright “star” in the east before sunrise. It rises about 6:30AM on the 27th, just above and to the left of the thin crescent moon. The moon moves on after this, but Mercury sticks around until after the end of October.

Venus is visible in the evening sky this month, very low in the west-northwest as the sun sets. See article above.

Mars is too close to the Sun to be visible this month.

Jupiter is low in the south as darkness falls, and is visible until about 10PM when it sets in the southwest. See details above.

Saturn has become a morning object, rising about 4AM and standing about 30° high in the southeast as dawn breaks. The rings are still visible, but our perspective is becoming almost edge-on, and so Saturn is fainter than usual.

Uranus is only visible to the unaided eye in very dark conditions. Binoculars and small telescopes show it as a pale green “star” with no details. Neptune is even fainter, and only visible with a telescope. The dwarf planets Pluto and Eris are unobservable without a large telescope. For locator charts, consult The Observer’s Handbook 2008, available from the Royal Astronomical Society of Canada.

Phases of the Moon for Manitoba:
First Quarter October 7, 2008 at 4:04 AM CDT
Full Moon October 14, 2008 at 3:02 PM CDT
Last Quarter October 21, 2008 at 6:55 AM CDT
New Moon October 28, 2008 at 6:14 PM CDT

Note: Phases of the Moon given here are in local time and date for Manitoba; they may differ by what is on your calendar because calendars often use “Universal Time”, the time and date at the Greenwich meridian in England. Greenwich time is 6 hours ahead of Central Standard Time and 5 hours ahead of Central Daylight Time. Sometimes this pushes the date of an event to the previous day for Manitoba.

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