Above: The ISS crosses the sky above Stonehenge in this composite of exposures by Tim Burgess of Wiltshire, UK taken on April 20, 2013

Young Moon and Venus in evening, Bright Planets at Dawn, and You Can’t Be Sirius!

Hey! Thursday morning is Groundhog Day! But why does it fall on February 2 each year? That date is one of the four so-called cross-quarter days, which are the midpoints between the solstices and equinoxes. February 2 is midway between the winter solstice and the vernal equinox, so we expect the weather to start being more spring-like and less winter-like. Astronomers don’t care too much if spring comes early — as long as the skies are clear.

The Moon and Planets

Tonight (Sunday), the thin crescent of the New Moon will hover prettily over the western horizon for an hour after sunset. On the following nights it sets later, shifting eastward while waxing towards Friday’s First Quarter phase. On Tuesday evening, January 31, the waxing crescent moon will form a tight triangle with Mars and Venus in the southwestern evening sky, easily fitting into a binocular field of view. Keep an eye out for the earthshine illuminating the moon’s darkened disk. As darkness falls next Sunday evening, February 5, look high in the southeastern sky for the Moon sitting less than a finger’s width to the lower left of the bright reddish star Aldebaran in Taurus the Bull. Parts of the world will see the moon pass in front of the star. As the evening wears on, you’ll see the moon pull away from Aldebaran.

Venus is now starting a slow descent towards the Sun, but it continues to shine brilliantly every evening in the western sky until it sets around 9:25 pm local time. Viewed in a small telescope, Venus will spend the next month or so shrinking from a “half-moon” shape (phase) to a thin crescent while growing in size. But it still hasn’t reached peak brightness! This week, Venus will continue to sit about a palm’s width to the lower right of dim reddish Mars, which sets about 9:50 pm local time. Blue-green Uranus is halfway up the southwestern sky at dusk — just inside the western (righthand) arm of the “V” that forms Pisces the Fishes. The planet sets just after 11 pm local time.

In early evening on Tuesday, January 31, shown here at 8 pm local time, the crescent moon joins Venus and Mars in the western sky.Image via Star Walk 2 app.

Don’t forget that the large asteroid Vesta is near peak brightness now (apparent magnitude 6.5), sitting about 4° (four finger widths) to the lower right of the bright star Pollux in Gemini the Twins in the evening eastern sky. Its rapid motion through the background stars can be noted by observing it on separate evenings. Ceres, another large asteroid, is observable now, too. It’s dimmer — but nicely positioned about four finger widths to the upper right of the modestly bright star Alrischa, which sits at the bottom of Pisces’ “V”.

The eastern pre-dawn sky contains Jupiter, Saturn and, for a few more days, Mercury, as shown here at 6:45 am local time on January 29, 2017. Image via Star Walk 2.

Bright, white Jupiter is rising in the east between 11 and 11:30 pm local time this week — and is sitting just a few finger widths from the bright white star Spica in Virgo the Maiden. By dawn, it’s moved above the southwestern horizon. Saturn is rising this week about 4:30 am local time, appearing as a yellowish dot low in the eastern sky until about 6:45 am. For a day or two more, Mercury can be glimpsed very low in the east for a few minutes centred around 6:45 am local time.

Trace the Winter Milky Way

If you missed last week’s guide to seeing the Winter Milky Way, it’s here.

You Can’t be Sirius!

The great winter star Sirius shines brightly low in the southern sky in mid-winter. In early evening, it sits in the southeast sky below Orion the Hunter. By 11 pm, it has reached its highest point, and sits due south. Sirius, also known as the Dog Star, is the brightest star in the constellation Canis Major the Greater Dog. It shines like a diamond inset into the dog’s collar. The pup’s head is to the upper left, with the body extending below it and the legs on the right (western) side. Canis Major is one of Orion’s hunting companions. The other, the more modest Canis Minor the Smaller Dog (featuring the bright star Procyon), sits to Orion’s left (east). The two dogs might be hunting Lepus the Rabbit, a constellation of medium brightness stars sitting right below Orion. Sirius has a tiny companion star, Sirius B that some astronomers call the Pup. I prefer to call it the Flea!

The night sky’s brightest star, Sirius the Dog star, flashes bright colours from its position low in the southern mid-winter evening sky, shown here at 9 pm. Image via Star Walk 2.

After our Sun, Sirius is the brightest star in all the sky. It is not only about 25 times more luminous than our Sun, but is only a mere 8.6 light-years away! On top of that, it is actually heading towards us, and will brighten over the next millennia! Sirius is famous for exhibiting flashes of intense colour as it twinkles. This is due to combining its brightness with the extra blanket of air it must shine though that low in the sky.

The ancient Egyptians linked their calendar to the arrival of Sirius in the pre-dawn sky because it signaled the onset of the Nile floods around the beginning of summer. In China, Sirius is called Tiān Láng天狼, aka “the Celestial Wolf”. Many First Nations cultures saw a dog’s shape in these stars and called Sirius the Moon Dog Star (Inuit), the Wolf Star (Pawnee), and the Coyote Star. Next clear evening, have a look at our bright neighbour!

Satellites

Iridium flares are glints of sunlight off of the flat reflecting sides of one of the satellites that comprise the Iridium pager and sat-phone network. The flares occur before dawn and after dusk, when the satellite passing overhead is still illuminated by the Sun, which is below the horizon for observers on the ground. The duration and brightness depend on the angles between the observer, the satellite, and the Sun. For even more info about Iridium Flares and the space station, see an article that I wrote here. Using an accurate clock, go outside a few minutes ahead and look in the direction indicated. You should first see the dim Iridium satellite moving quickly across the sky, and then it will rapidly brighten for 3 to 8 seconds, and fade out. Truly spectacular! The more negative the Magnitude number, the brighter. The larger the Alt. number, the higher up it is! (The horizon is 0°, and 90° is straight up, so 55° is a bit higher than halfway between the horizon and zenith.) These data are adapted from www.heavens-above.com. To get your own schedule, enter your location in their website.

The ISS (International Space Station) is also visible at times, gliding silently overhead. If you enter your location in the www.heavens-above.com website, you will get a list of them for wherever you might be.)

Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.

Stargazing News for this week (from January 29th) by Chris Vaughan.