The Crescent Moon meets Evening Planets, and Our Place in the Galaxy!
The Moon and Planets
As the week opens, the moon is hidden beside the sun’s glare, reaching new moon on Sunday at 9:58 am EST. At this new moon, the moon passed in front of the sun, producing an annular solar eclipse. Six months from now, the alignment happens again, with the total solar eclipse visible across the USA on August 21. Much of North America will see a partial eclipse.
The delicate young crescent moon will shift away from the sun, becoming briefly visible low in the western sky after sunset Monday, then climbing higher and waxing thicker each evening. From Tuesday to Thursday, the moon will gather with bright Venus and dim red Mars in the early evening western sky. The objects will all be within about 16° (1.6 closed fist diameters) of one another, making a lovely widefield or telephoto photo op! As a bonus, tiny dim Uranus will be there, too, just two finger widths below Mars.
In the western sky during late evening on Saturday, March 4, observers in the south of the Great Lakes will see the first quarter moon briefly pass in front of (occult) the bright star Aldebaran in Taurus (the Bull). The dark leading edge of the moon will cover the star first, and then it will emerge from the opposite illuminated limb some time later. Times and duration vary by region, so observers should begin to watch before 11 pm EST. In a narrow zone stretching from Vancouver to Toronto, observers will see the moon’s northern edge graze the star, or pass very near to it. As the moon’s mountains and valleys pass the star, it will appear and disappear over a timescale of seconds. As the moon crosses the entire face of Taurus before reaching Aldebaran, it will occult two less bright stars Hyadum III and Hyadum IV between 6:52 and 6:59 pm EST.
Bright white Venus continues to catch the eye, low in the western evening sky after dark, setting about 9 pm local time. A telescope will reveal that it is showing a waning crescent phase that is slowly growing larger as it moves towards Earth, on its way towards inferior conjunction with the Sun next month. Much dimmer, reddish Mars is starting to set earlier, about 9:45 pm this week. The planet is easily identified because it sits about a fist’s diameter (11°) to the upper left of Venus. The two planets are now slowly drawing apart again.
Visible as soon as it’s dark on Sunday evening, February 26, Mars will sit only 34 arc-minutes (about the moon’s diameter) to the upper right of blue-green Uranus. The pair of planets will be in the lower third of the western sky, situated between the strings of stars defining the two fishes of Pisces. The two planets should fit together in the field of view of a low power eyepiece, regardless of telescope.
Bright, white Jupiter, situated just a few finger widths to the upper left of the bright white star Spica in Virgo (the Maiden), is rising in the east about 9:30 pm local time this week. By dawn, it’s moved above the southwestern horizon. Jupiter’s moon Io casts its black round shadow on the planet at Mar 2 from 2:05 to 4:10 am EST and from 9:45 to 10:40 pm on Mar 3. The Great Red Spot is visible on Jupiter for about two hours centred on Feb 28 at 12:40 am EST, Mar 2 at 2:20 am EST, Mar 2 at 10:15 pm EST, and Mar 4 at 11:55 pm EST.
Yellowish Saturn rises in the southeast before 3 am local time, and can be spotted until about 6:15 am, when it’s two fist diameters above the southern horizon. The bright reddish star Antares in Scorpius (the Scorpion) will sit less than two fist diameters to the right (southwest) of the planet for the next few months.
Our Place in the Galaxy
The bright stars we see in the night sky are other suns. Although stars can be inherently brighter or dimmer based upon their age, size, and composition, the brighter ones are generally our nearest neighbours, while the dimmer ones (many of which emit far more light than our Sun) are farther away.
Our galaxy is shaped like a disk containing a stubby elongated central bulge surrounded by a tapered rim composed of spiral arms — dense concentrations of stars, gas, and dust that wrap around the core. This is a known as a barred spiral type galaxy. It’s about 180,000 light-years across and a few thousand thick, containing up to 400 billion stars, many of which likely have one or more planets! Our solar system is situated about halfway between the galactic core and the rim, and we orbit the core once every few hundred million years. For scale, if our solar system was the size of a quarter, the galaxy would stretch between Canada’s east and west coasts!
The brightened strip of sky that we call the Milky Way is the cross-section of the galactic disk, where most stars are concentrated, projected against the night sky. Because the disk has a thickness to it, and we’re embedded inside, we are completely surrounded by stars in every direction. Our Solar System and all our nearby starry neighbours occupy a place within one of the minor spiral arms. Astronomers refer to it as the Orion Arm because the dominant stars in the winter constellation of Orion (the Hunter) mark its position. The Orion Arm actually sits between two major arms — the Perseus Arm and the Carina-Sagittarius Arm.
In the summertime, the night sky (over our southern horizon) points towards the Carina-Sagittarius Arm and beyond — into the core of our galaxy. In the winter months, our night-time sky shows the opposite direction, outwards beyond Orion and into intergalactic space. From a dark sky location, the sky along the Milky Way is especially rich in open star clusters (where stars have recently been formed and not yet dispersed) and nebulae (where stars will soon be formed or have just started to shine).
Our galaxy is only one of billions we know of in our observable universe. But to see other galaxies, we have to see past the stars, gas clouds, and dust in our own. Every year during April and May, the Milky Way hugs the evening horizon, allowing us to gaze overhead into the deep universe at other galaxies. By the way, using other wavelengths of light, astronomers can tell that there are large galaxies hidden from our view by the bulk of our galaxy.
The nearest major galaxy to us is the Great Andromeda Galaxy or Messier 31 (M31). In appearance, it’s a twin to our own, although it is twice as massive. At 2.5 million light-years away, it is one of the most distant objects visible to unaided human eyes! The Milky Way is approaching the Andromeda Galaxy at about 400,000 km per hour, but we won’t make contact for four billion years. When we do, don’t expect a crash — there is so much empty space between the stars that the two will pass through one another like two puffs of smoke. Our mutual gravity will eventually pull us into a complicated dance that will merge the two galaxies into something new! When you’re out this winter, look for M31 high in the western sky above the great square of Pegasus. It’s a large dim glow, actually six times wider than a Full Moon!
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 February 26th) by Chris Vaughan.