This is the 100th episode of ‘What’s Up’ and we thank JPL/NASA and Jane Houston-Jones in Pasadena, CA. Here we share some of Jane’s favourite celestial things. Luckily October is a great month to see them. Let’s count down, beginning at sunset.
10. As the sun sets in the west over Metchosin, watch its colour. At sunset and sunrise, sunlight travels a long path through the atmosphere to reach our eyes. The thick atmosphere absorbs most colours of sunlight, but red light is absorbed the least, so we often see a sunset in shades of red. Rarely, green flashes can be seen just above the sun’s edge just as the last sliver of its disk disappears below the horizon.
9. Just after sunset, turn and face east toward Mount Baker. You’ll soon see a dark shadow move up from the horizon and gradually cover the pinkish sky. This is called Earth Shadow, or the Belt of Venus. Earth itself is blocking the sunlight. The lower the sun sinks, the higher the shadow rises in the sky.
8. Also just after sunset (or before dawn) you may see rays of sunlight spread like a fan. These are crepuscular rays, formed when sunlight streams through gaps in clouds or mountains. Anti-crepuscular rays look the same but appear opposite the sun.
7. The bright flowing lights of the aurora borealis, or northern lights, are the result of collisions between gaseous particles in Earth’s atmosphere with charged particles released from the sun.
The different colours are due to the type of gas being struck by particles of the solar wind. Yellow-green aurorae are produced by oxygen molecules about 60 miles above Earth; red aurorae are from oxygen 200 miles above Earth and purple or blue is from nitrogen. In Oak Bay we usually see green waves of silk across the sky, not the multi-coloured aurora you might expect.
Learn more at www.swpc.noaa.gov/products/planetary-k-index
6. The Andromeda Galaxy is one of the few galaxies you can actually see with the naked eye. In October, look nearly overhead after sunset. The galaxy is more than twice the apparent width of the moon – so big that it barely fits in the field of view of a telescope at medium magnification.
5. Oct. 19 is Astronomy Night at the U.S. White House, and the nights around the 19th are excellent for viewing features on the moon such as the Sea of Tranquility and the site of the 1969 Apollo 11 landing.
4. This month the European Space Agency’s Rosetta Mission target, comet 67P Churyumov-Gerasimenko, is still bright enough for experienced astronomers to pick out in a dark sky. On Oct. 9, you may be able to spot it through a telescope in the east over Bellingham near the crescent moon and Venus.
3. There are meteor showers galore this month – the faint, slow-moving Draconids on Oct. 9, the slow, super-bright Taurids on Oct. 10, and the swift and bright Orionids from the dust of Comet Halley on Oct. 21. A given meteor shower happens annually – when the earth returns to the point in its annual orbit where it crosses the orbit of the comet. That is why each meteor shower reoccurs every year like clockwork. A given meteor shower (say Taurids) will always get less and less intense as the tail thins. Only when the comet returns will the brightness suddenly shoot back up the maximum.
2. On Oct. 28, you’ll find a tight pairing of Jupiter, Venus and Mars in the Eastern sky over Mount Baker before sunrise.
1. We’ll end this list with our favourite astronomical sight — the Zodiacal Light. It’s a faint triangular glow seen from dark skies after sunset or before sunrise. This is sunlight reflecting off dust grains that circle the sun in the inner solar system. These dust grains travel the same pathway — called the ecliptic — as the moon and planets as they journey across our sky. These are the same dust particles the Rosetta Mission was sampling on its eight-year journey to Comet 67P. I’ll leave you with the question – what are these particles made of?
If you’re lucky enough this month to see the Zodiacal Light, sometimes called the “false dawn,” Jupiter, Venus and Mars will be just above it.
Find NASA resources for armchair astronomy at SolarSystem.nasa.gov/StarToolBox.
Summarized “What’s Up In October 2015” by NASA announcer and astronomer Jane Houston Jones with permission for localization to Cattle Point Urban Star Park and the Oak Bay News. Bill Smith and the RASCals are volunteers at the Cattle Point Dark Sky Urban Star Park.