Image from NASA of Orion

Minnesota Skies: February 2020

Your local guide to observing celestial objects and events

Published01/30/2020 , by Deane Morrison, Thaddeus LaCoursiere & Sarah Komperud

A dazzling evening “star,” Venus comes out in twilight and sticks around long enough to outshine all the real stars against a dark sky. So bright is our sister planet, it has been mistaken for a UFO. Watch it climb in the southwest throughout the month, and be sure to catch it on the 26th and 27th, when a waxing crescent moon appears near it.

The moon takes many partners this month, especially as it tours the group of bright winter constellations now moving onto center stage in the southern sky. On the 3rd, a bright moon crowds the face of Taurus, the bull, and its bright star Aldebaran, the bull’s eye. On the 6th, a fatter moon will shine near the Gemini twins Pollux (the brighter) and Castor.

February’s full moon rises in the late afternoon of the 8th and reaches fullness at 1:33 am on the 9th. This full moon will be quite big and bright, since the moon reaches perigee, its closest approach to Earth in an orbit, only about a day and a half later.

In the morning sky, the three outer planets—Mars, Jupiter and Saturn—are positioning themselves for a spectacular dance in March and early April. All rise in the southeastern predawn sky; Mars first, then Jupiter and finally Saturn, which may be too low to easily see until the last few days of the month. When the three planets are all above the horizon, they will form a nearly straight line, with brilliant Jupiter in the middle.

On the 18th, a thick waning moon passes in front of Mars, making the red planet disappear behind the moon’s illuminated side. Mars may be hard to see next to the moon’s glare, and the time of Mars’s disappearance varies slightly by location. But if you get out by 5:45 a.m. you should be able to watch the event.

On the 2nd, we celebrate an astronomically based Celtic holiday known as Imbolc, or lamb’s milk. It was one of four cross-quarter days falling midway between a solstice and an equinox. It was held that a sunny day predicted cold and continued winter, but a heavily clouded, shadow-free day portended warm spring rains that would soften up the fields for planting. This myth survives in modern Groundhog Day rituals; if the groundhog sees its shadow it means six more weeks of winter, whereas thick clouds mean spring is right around the corner.

Excerpted from Minnesota Starwatch by Deane Morrison, a publication of the Minnesota Institute for Astrophysics at the U of M. 

Featured image: Venus shines brilliantly in the subtle pre-dawn glow looking to the East over a small frozen inlet with The Milky Way above, March 18, 2014.

Sky-lights

February starts off with the easiest and hardest planets to see with the naked eye visible in the early evening sky. Venus—the brightest planet visible to us and the brightest celestial object in the sky besides the Sun and Moon—remains to the southwest as it has been for several months. Continue watching it as the month goes along, as it will appear higher and higher above the horizon. This trend will continue into the end of March when Venus reaches its greatest eastern elongation from the Sun.

Elongation is both a fun word to say and an important concept in astronomy. A planet’s elongation is the angular distance between the planet and the Sun as seen from the Earth. For a planet like Venus, its angular distance between it and the Sun is never more than about 50 degrees. 500 years ago Nicolaus Copernicus used this fact to support the heliocentric model of the solar system (where the Sun is at the center of the solar system and the planets, including the Earth, orbit around the Sun). If the alternative geocentric model was correct and the Earth was the center of the solar system, then at times Venus could be directly opposite the Sun as seen from the Earth, and Venus’s elongation would be 180 degrees (a straight line from the Sun, through the Earth, to Venus). But we never observe this happening with Venus, or with the other planet closer to the Sun than the Earth: Mercury.

Mercury’s greatest elongation is never more than 30 degrees, and we’ll find it 20 degrees above the horizon on February 10. This is the highest above the horizon we’ll see Mercury in February, and also the easiest to see. If you go out about 20 minutes after sunset and spend some time searching the west-southwestern sky, you should be able to find a tiny point of light—that’s Mercury! To help find it, stretch your arm out with your hand in a fist. Mercury should be about two fist-widths above the horizon.

Even at its greatest elongation, Mercury is never easy to see: it’s still the smallest planet at just 3,000 miles across (only 1,000 miles wider than our Moon!) and Mercury’s dark rocky surface only reflects about 7 percent of the sunlight hitting it. In contrast, Venus’ atmosphere reflects 75 percent of the sunlight hitting it! There are some simple things you can do though to make it easier to find Mercury while it’s visible in our sky throughout all of February:

  • Get higher up. This won’t change Mercury’s distance from the horizon, but if you get on top of a building or the highest point near you, you get above the trees and other buildings that can block your view. Looking across large flat open areas like fields or lakes can also help.
  • Look more than once and for more time than you expect. In astronomy, experience is key, and every time you go look at the sky you’ll get better and better at spotting tiny objects like Mercury.
  • Check out your local astronomy club. For almost 50 years the Minnesota Astronomical Society has been helping people experience the majesty of the night sky. With monthly meetings and star parties, there are dozens of opportunities throughout the year to get some help observing the night sky. More information is available at www.mnastro.org. Other astronomy clubs can be found through a simple online search of your city name, state, and astronomy club.
  • Come to a Bell Museum star party! These free monthly events are open to everyone and include telescope observing and a brief presentation in the Whitney and Elizabeth MacMillan Planetarium about objects we can see in the sky. Although we can never guarantee clear skies and every object visible, it’s always a fun time!
  • Use an app! There are multiple star chart or sky map apps available for different devices. Some are free and some cost money. The quality of apps vary, but even one that just allows you to get oriented to the cardinal directions will help make sure you’re looking the right way.
  • Don’t look at the Sun! Blinding yourself will make it very difficult to see Mercury or anything else.

When viewing planets, stars or other objects in the night sky, it is helpful to use a sky map. You can download our Minnesota Skies guide or customize your own map on stellarium-web.org. Minnesota Starwatch is another great resource. Meet up with other stargazing enthusiasts via Twin Cities Sidewalk Astronomers, MN Astronomical Society & MN Institute for Astrophysics.


Lunar Highlights

February 1—First Quarter Moon
The Moon is one quarter of its way through its orbit around
the Earth, which makes half the Moon illuminated and half
dark from our perspective.

February 9—Full Moon
The Moon is located on the opposite side of the Earth as the
Sun and the side we see is fully illuminated.

February 15—Last Quarter Moon
This phase occurs when the Moon is three-quarters of the
way through its orbit around the Earth.

February 23—New Moon
The Moon is located on the same side of the Earth as the Sun
and is not visible in the night sky. This is the best time of the
month to observe faint objects like galaxies and star clusters
because there is no moonlight to interfere.

Deep Sky Objects

High above our heads, the magnificent arch of the Milky Way continues to fill the sky, visible for hours each night. The wealth of the Milky Way lies not only in the sight of the entire band, but also what can be found all along the milky road across the sky: open star clusters!

Locating these clusters is a fantastic way to understand the life of stars. In January, we highlighted how to find the Great Orion Nebula, or M42, a star-forming nebula. After stars form in nebulas like M42, their mutual gravitational pull draws large groups of them together. They remain together for a short time before the internal movement of the stars in the cluster and close encounters with other clusters causes the cluster to spread apart. Eventually many of the stars end up isolated. Because that dispersion hasn’t happened yet, when we look at an open cluster, we can see stars of similar ages, chemical compositions, and distances from the Sun. This makes open clusters space laboratories for scientists studying interactions between stars, how different stars evolve, and how the chemistry and structure of galaxies evolve.

The most famous open cluster is easily found high to the south at around 8 pm: the Pleiades—also known as the Seven Sisters or Messier 45. If you’ve never seen it before, start at Orion’s Belt and head upward in the direction the belt points. A hand length away you’ll see a bright red star: Aldebaran. Continue on another hand width to find the Pleiades, looking almost like a small scattering of seeds in the sky, a small dipper, or a question mark. These stars have been traveling around the disc of the Milky Way since they formed around 100 million years ago. They’ve left their parent nebula behind, and the Pleiades is moving through a denser cloud of galactic gas and dust. The haze around the stars is a good target for beginning astrophotographers just learning about long-exposure photography.