The March Night Sky 2017

Goodbye February, the shortest month of the year, and hello March! The desperate chill of winter is starting to lift and at the end of this month we will have the March Equinox. On the 20th March the Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. The March equinox marks the first day of spring in the northern hemisphere and the first day of autumn in the southern hemisphere. The March equinox is the first equinox of the New Year, with the second occurring in September.

If you come to the Armagh Observatory and Planetarium visit our stone circle on top of the Hill of Infinity.  Here are laid out stone markers showing the passage of the seasons at the equinoxes and solstices.  You will be able to see that the Sun rises due East and sets due West on the equinox by standing directly behind the marker stones.  And at the same time you will have a spectacular view over the City of Armagh!

 

Armagh as seen from the Stone Circle on top of the Hill of Infinity

 

A special experiment can also be carried out on this day. To do this experiment, you’ll need a straight stick or a long wooden ruler, a protractor and a compass.

Find an empty space such as a park or a carpark where there are little to no tall buildings, trees or hills to obstruct the Sun. Find your location’s latitude. You can do this by using either, online latitude and longitude websites, or you can use apps like Google Maps. Then you have to subtract this number from 90. This will be the angle you will affix the stick in the ground.

 

Solar Equinox as seen on Earth. Video Credit: NASA, Meteosat, Robert Simmon, APOD 

 

If you are in the Northern Hemisphere, use your compass to find south and point the stick in that direction. If you’re in the Southern Hemisphere, point the stick or the ruler to the north. Using the protractor fix the stick in the ground at the angle you just calculated – remember to point it in the direction opposite to the hemisphere you are on.

For the next step of this experiment you will have to be patient. Wait till Noon and hopefully you’ll see the shadow of the stick disappear. At Noon, the stick will have no shadow at all!

The 12th March will see a full moon in the night sky. The Moon is the Earth’s natural satellite and the rise and fall of the tides on the Earth is caused by the effect of the Moon. There are two bulges in the Earth due to the gravitational pull that the Moon exerts; one on the side facing the Moon, and the other on the opposite side that faces away from the Moon. The bulges move around the oceans as the Earth rotates, causing high and low tides around the globe. The moon makes a complete orbit around Earth in 27 Earth days and rotates at that same rate. As the Earth is moving as well, rotating on its axis as it orbits the sun, from our point of view, the moon appears to orbit us every 29 days.

 

The moon’s heavily cratered surface is the result of intense bombardment by meteorites between 4.1 billion and 3.8 billion years ago. The scars of this time, seen as craters, have not eroded for two main reasons: The moon is not geologically very active, and with no atmosphere there is also no wind or rain, so very little surface erosion occurs. Image Credit, Armagh Planetarium

 

March 28th will see a New Moon in the sky, and so it will not be visible to us. If you are planning to do any stargazing, not having the moon visible in the sky is the opportune moment. If you’re new to stargazing, we always recommend starting out with a good pair of binoculars as they are a cost effective way of viewing the night sky. If you’re wondering what to look at in the night sky in March here are a few recommendations from us:

The constellation of Orion the Hunter will still be in the sky at roughly 11 o’clock at night, however he will be low on the horizon, and this may be your last chance to see him before he disappears for another season.

 

Orion is visible in both the Northern and Southern hemispheres. In the Northern hemisphere the constellation can be seen from late autumn to early spring. In the Southern hemisphere Orion can be seen in the summer months, note that it will appear upside down. Image Credit: Heather Taylor; Stellarium

 

We thoroughly recommend having a look at the star Betelgeuse and the star Rigel. These two stars are great for new stargazers to spot as they are different colours. Betelgeuse is a red giant star located 640 light-years away from the Earth. Rigel is a blue-white super giant, and is not just a single star, it is in a binary system. It is located roughly 800 light-years away from the Earth.

Also located quite close to the horizon at this time is the brightest star in the night sky, Sirius. Sirius is known as the “Dog Star,” and can be found in the constellation of Canis Major the Great Dog. Sirius is situated 8.6 light years away from the Earth and has an apparent magnitude of -1.47. This will be one of the last times you will be able to see the extremely bright star before it disappears below the horizon.  It is the brightest star in the sky.

 

Canis Major is the 43rd biggest constellation in the sky, occupying an area of 380 square degrees. Canis Major is commonly taken to represent the “greater dog” following the hunter Orion in Greek myth. Image Credit: Heather Taylor; Stellarium

 

Appearing in the sky and fully announcing the arrival of the new season are some constellations that you can only see in spring time. One of the most iconic constellations in the spring night sky is Leo the Lion. This constellation is a member of the signs of the zodiac, and is one of the most recognisable with its backwards question mark shaped head. This asterism found in Leo can also be referred to as The Sickle. The brightest star in Leo is called Regulus, and it marks the bottom of the backwards question mark.

 

Leo is the Nemean Lion, which was killed by Hercules on one of the 12 labours he had to perform for killing his family. According to Greek mythology, the lion that terrorized the citizens had a hide that could not punctured by iron, bronze or stone. Having broken all of his weapons fighting the man-eating lion, Hercules finally strangled it to death and placed it in the heavens as one of his conquests. Image Credit: Heather Taylor, Stellarium

 

Regulus, also known as Alpha Leonis, is roughly 79 light-years away from the Earth. Regulus is a multiple star system, and naturally this cannot be seen directly with the naked eye. Regulus A is the dominant star, with a binary companion, and Regulus B, C and D are located further away. The Regulus system is the twenty-first brightest star in the night sky.

Making her grand appearance in the sky in March is the constellation of Virgo the Maiden, another member of the signs of the zodiac. Virgo is the second largest constellation in the night sky, and the brightest star in this constellation is called Spica. Spica, also known as Alpha Virginis, is the sixteenth brightest star in the night sky and is a spectroscopic binary.

 

Virgo is a brilliant constellation with 26 known exoplanets (planets outside of the solar system) orbiting around 20 stars. It also has at least a dozen Messier objects. It is the largest constellation of the Zodiac and the second-largest constellation overall, behind Hydra. Image Credit: Heather Taylor, Stellarium.

 

Spectroscopic binary stars are found from observations of radial velocity. The brighter member of such a binary can be seen to have a continuously changing periodic velocity that alters the wavelengths of its spectral lines in a rhythmic way; the velocity curve repeats itself exactly from one cycle to the next, and the motion can be interpreted as orbital motion. In some cases, rhythmic changes in the lines of both members can be measured.

Another constellation to have a look out for this month is Hydra, the largest and longest constellation in the night sky. Despite its size, Hydra is not really made up of many bright stars, however its brightest star is called Alphard. It is three times the mass of our sun and is estimated to be 420 million years old. It is a giant star so has already evolved out of its main sequence.

 

In the past the star Alphard, or Alpha Hydrae, was also known as “Cor Hydrae”, the “heart of the serpent”, which was a name given to it by the famous Danish astronomer Tycho Brahe. The name Alphard derives from the Arabic for “the solitary one. Image Credit: Heather Taylor, Stellarium.

 

Hydra has some fascinating deep sky objects contained within its boundaries. NGC 3242 is one of them and is more commonly known as “The Ghost of Jupiter.” This was discovered by William Herschel in 1785. This planetary nebula is frequently called the Ghost of Jupiter, or Jupiter’s Ghost due to its similar size to the planet, but it is also sometimes referred to as the Eye Nebula. The nebula measures around two light years long from end to end, and contains a central white dwarf with an apparent magnitude of eleven. NGC 3242 can easily be observed with amateur telescopes, and appears bluish-green to most observers. Larger telescopes can distinguish the outer halo as well.

There is no doubt that the March Night Sky has some amazing things to see, and we would encourage you to have a look at these, in particular the constellation of Orion and Canis Major, before they disappear completely from the sky. Don’t forget to wrap up warm when you’re heading out to star gaze and remember to avoid light polluted areas.

 

Article written by Heather Taylor, Education Support Officer

Heather Taylor, Education Support Officer