Messier Objects - M18

The northwestern region of Sagittarius is filled with amazing objects to view with a telescope.  The Milky Way goes right through this area filled with many star clusters.  Messier 18 is located here and can be found in the evening during the middle of the Summer.  The Summer is sometimes difficult to observe dim objects in the sky due to the unceasing twilight.  However, by later July and August the sky once again dips into night and deep sky objects are easier to find.

Messier 18 is an open cluster found a degree and a half North of the Sagittarius Star Cloud, M24.  At 9 light years in diameter it is smaller than the nearby M25.  It is also more than twice as far away as its neighbour measuring 4900 light years distant from Earth.  This means it is also quite a lot dimmer with an apparent magnitude of 7.5.  This makes it invisible to the naked eye and thus requiring binoculars or a telescope to resolve.  M18 appears as 9 arcminutes in diameter which is about a third of the size of a Full Moon.

Observation Information

This object was part of my Sagittarius marathon I had during the early Summer weeks of 2018.  At this time Saturn was sitting right in the middle of the Sagittarian Messier heartland.  Messier 24 was located just North of the ringed planet and the bright star Mu Sagittarii.  Using the bright star cloud as a guide I slew the telescope North by one field of view.  I was using a 14" reflector with a 41mm (68° FOV) which created a true field of view of 1.39°.

I saw an open cluster of stars that was sparser than most clusters I have observed.  However, I did recognize a 'Big Dipper' type asterism located within the cluster.  There were 6 relatively bright stars aligned in the formation of a spoon.  I hope to come back to this object in future weeks to see if it is familiar and recognizable.  I measured the cluster to be approximately 20% across the field of view of my 13mm (82° FOV) eyepiece.  This corresponds to an observed value of 7.8 arcminutes which is close to the accepted value of 9 arcminutes.

The weather information at this time is listed in the table below.

Characteristic	Value
Temperature	24°C
Humidity	39%
Wind	N 6 km/h
Barometer	101.91 kPa
Sky	Passing Clouds

The observation record for M18 is found below.

M18 Observation Record

Additional Information

This cluster of stars was first discovered by Charles Messier in 1764 and he reported it as follows.  "In the same night, I have discovered a bit below the nebula reported here above, a cluster of small stars, environed in a thin nebulosity; its extension may be 5 minutes of arc".  The nebula Messier is discussing is M17 which is located just North of M18.  Later observations of M18 in the 19th century indicate no nebulosity.  Admiral William Smyth quipped: "This cluster was discovered by Messier, and registered as a mass of small stars appearing like a nebula in a 3 1/2-foot telescope; which affords another instance that the means of that very zealous observer did not quadrate with his diligence".

Research in 2009 has indicated that M18 is a binary cluster companion to M17.  Both objects are stunning through any telescope and should be sought out on a clear Summer evening.

2018 Week 30: (July 22-July 28)

We have just had another decent week for viewing.  It may have been a tad humid on a few occasions but the waxing crescent Moon was in the sky.  THIS IS THE WEEK we have all been waiting for.  This will likely be one of the stories of the year.  Mars will reach opposition Thursday evening at 23:00.  It will then reach its closest approach several nights later on the morning of July 31 at 02:00.

We have been building up the Mars event over the past few weeks and months.  It will be at its biggest and brightest since 2003 and will not be this close again until 2035.  This is a do not miss event!

The details for the week are presented in the table below.

Date	Event
July 25	Saturn 2°S of Moon
July 26	Mars at Opposition
July 27	Full Moon
July 27	Total Lunar Eclipse
July 27	South Delta-Aquariid Meteors Peak

First of all, do not get excited about the total lunar eclipse.  It will not be visible from Canada.  Actually, Cape Spear in Newfoundland (easternmost point in Canada) will have the Moon's penumbra appear on lunar surface for 19 minutes.  This will not be discernible to the naked eye.

On Tuesday night it might be worth it to head out around 0:00 MDT.  Saturn will be sitting just below the moon.  They can be seen in the same binocular field or wide field telescope view.

Friday night through into early Saturday morning the Southern δ-Aquariid Meteors peak.  This is an annual shower that occurs at the end of July each year.  The maximum estimated rate is usually around 20 per hour under perfect conditions.  Expect to be lucky to catch 5 an hour under suburban skies.  The radiant point is located just east of Delta Aquarii in the constellation Aquarius.  The Full Moon will be in the constellation next door which will add to the light pollution.

Delta Aquariid Radiant

The highlight of the week will be Mars.  Astronomers have been waiting years for this close Martian opposition.

If you would look in the southeastern sky an hour or two after sunset you would see a bright yellow ball of light.  Mars is usually red but with a global dust storm encompassing the planet it appears more yellow than red.  This is quite unfortunate as it will be difficult to see surface features on Mars.  I was hoping to see Mount Olympus and Syrtis Major Planum from my backyard!  It seems we may be lucky to catch a polar ice cap!

If you would like to explore the surface of Mars NASA has a great interactive program that can be found at the link below.

https://mars.nasa.gov/maps/explore-mars-map/fullscreen/

NASA's Explore Mars Map

Mars will remain relatively large in our sky (>20") until the first week of September.  Hopefully the dust storm will settle between now and then.  It will once again be larger than 20" (although not as large as this year) throughout September and October 2020.  However, after 2020 we won't see Mars break the 20" barrier until the mid 30's.

Get outside and see the planets march across the southern sky and know that you will not see Mars this bright again until 2035!

Messier Objects - M25

Sagittarius is full of amazing sights with the naked eye, binoculars and a telescope.  If you live in an urban setting it is best to use optical aid.  There are plenty of star clusters located throughout the heart of our Milky Way galaxy.  One such cluster is known as Messier 25.  It has no special name associated with it but it is quite beautiful.  As with all objects within this constellation the best time to view them is during the Summer.

Messier 25 is an open cluster located in the northwestern region of Sagittarius.  It can be found a mere 6.5° away from the Sagittarius Star Cloud, M24.  It is approximately 19 light years across and it located 2000 light years from Earth.  As viewed from Earth it appears as 32' in diameter; the approximate width of the Full Moon.  It is possible to see it with the naked eye as its apparent magnitude is 4.6.  However, it would be difficult to see from an urban or suburban setting due to light pollution.  

Observation Information

I first located this Messier Object late in the evening of July 8, 2018.  After I had observed M24 I slew my telescope eastward approximately two fields of view.  I noticed three brighter stars above the cluster that seemed to encompass the deep sky object.  I found this object using my 14" reflector telescope with a 41mm (68° FOV) Televue Panoptic eyepiece.  This produced a true field of view of 1.69 degrees.  The tight part of the cluster seemed to take up 40% of the field which works out to an estimate of 41'.  There seemed to be a lot of stars outside of the main cluster.  This is likely due to the rich nature of the Sagittarian region.

The weather information at this time is listed in the table below.

Characteristic	Value
Temperature	24°C
Humidity	39%
Wind	N 6 km/h
Barometer	101.91 kPa
Sky	Passing Clouds

The observation record for M25 is found below.

M25 Observing Record

Additional Information

This cluster was discovered before the time of Messier in 1745 by the Swiss astronomer Jean-Philippe Loys de Chéseaux.  He originally commented: "Another one between the bow and the head of Sagittarius".  Nearly twenty years later Charles Messier recorded this object in his famous catalogue.  Messier noted that the stars of the cluster were seen with some difficulty with an ordinary telescope.  He also noted that it contained no nebulosity.

It is interesting to note that this cluster does not have an NGC number associated with it.  It does however have an Index Catalogue number which means it was included in the major update to the NGC.

If you are ever searching the realms of Sagittarius be sure to seek out M25.

Messier Objects - M24 (Sagittarius Star Cloud)

During the Summer the constellation Sagittarius makes its way in our evening sky.  It is a remarkable region as the Milky Way is highly concentrated as it contains the galactic center.  It is thus home to an exceptional amount of star clusters.  Messier 24 is one such grouping of star, however it is known as a star cloud.  It lies in the Sagittarius Arm next to our own Orion Spur in our area of the galaxy.  For more information on our galaxy's structure see the link below:

http://simonjastronomy.blogspot.com/2018/07/the-milky-way-galaxy.html

The cloud is about 600 light years wide and contains stars 10,000-16,000 light years distant.  Viewed from Earth it will seem to take up an area nine times larger than the Full Moon.  This makes it best to see in a wide-field low power telescope.  A lot of people think low power telescopes are useless.  That is the furthest from the truth, with good optics, they showcase many great wide-field objects.

It is amazing that this cloud contains millions of stars as it is representative of the heart of our galaxy.  Since it is so rich in stars, dark nebula are much easily observed.  Simply put, a dark nebula is a region of gas and dust that obscures the light behind it.  This makes it look pitch black compared to the surrounding area.  The Horsehead Nebula is an example of this phenomenon.

Observation Information

On July 8, 2018 I was able to observe Messier 24 from my backyard.  I was fortunate that it only sat a few telescope fields of view above the bright planet Saturn.  However, I knew Saturn would not always be there so I intended to use stars to guide me to its location.  I used my red dot finder to locate the naked eye star Lambda Sagittarii, the top of the teapot asterism.  Once I had this star in my sight I slew the telescope northward towards a dimmer naked eye star Mu Sagittarii.  M24 lay just one field of view northeast of this star.

It is important to note that at this time I was using a 14" reflector with a focal length of 1650mm.  The eyepiece of choice was a 41mm (68° FOV) Televue Panoptic.  This gave me a true field of view of 1.69 degrees or 101.4 arcminutes.  This is just over three times the diameter of the Moon making it the perfect field for M24.

The weather information at this time is listed in the table below.

Characteristic	Value
Temperature	24°C
Humidity	39%
Wind	N 6 km/h
Barometer	101.91 kPa
Sky	Passing Clouds

It first appeared as a loose collection of bright stars filling the entire field of view.  As I used averted vision it seemed as though the whole field was filled with stars.  It was difficult to measure how large the star cloud was but it appeared to be nearly 2° in diameter.  Astronomical records indicate it is 90' in diameter which is equivalent to 1.5°.

M24 Observation Record

Additional Information

The star cloud contains clusters within its borders most notably NGC 6603 that can be found with a telescope.  There are also a couple planetary nebula that may also be viewed with a keen telescopic eye.

This star cloud has been documented for centuries.  The great comet hunting Charles Messier included it in his 1764 catalogue denoting it as considerable nebulosity about a degree and a half extension.  Other astronomers have taked note of it throughout the 19th and 20th century.  It has been also referred to as 'Delle Caustiche' by famous astronomer Father Pietro Angelo Secchi.  Translated to English this basically means 'of the burning'.

If you find yourself in a dark site at some time throughout the years look above the lid of the teapot and see if you can find this amazing star cloud!

Constellation Profile - Sagittarius

The constellation of Sagittarius is well known as it one of the most popular in the zodiac.  The zodiac is a region in the sky approximately 8° North and South of the ecliptic.  This is the area of the sky the Sun, Moon and Planets transit.  If you were to look at the planets in the sky they would likely be within the borders of a zodiac constellation.

There are several myths associated with Sagittarius.  It is well known that this constellation represents the archer.  The Greeks represent Sagittarius as a centaur who is aiming his arrow toward the heart of Scorpius--the bright red star Antares.  In mythological tradition the scorpion killed Orion and is now seen chasing the great hunter out of the sky in the Spring.  Sagittarius keeps a watchful eye on Scorpius to ensure he does not sting Orion again.

The chief librarian at the Library of Alexandria, Eratosthenes, believed that Sagittarius represented a satyr and not a centaur.  The satyr Crotus is a mythological being known to be the son of Pan.  He is credited with inventing archery and was an excellent hunter.  He kept the company of the Muses and is also credited with inventing applause.  The Muses, in their great love for him, requested Zeus to put him in the sky.

Sagittarius (Artist Interpretation)

For observers in Calgary, most of Sagittarius can be found transiting the southern sky just above the horizon throughout the Summer around midnight.  If you are at a dark site you will notice the Milky Way and the Galactic Center find their home in this constellation.  Within the constellation, the radio signal known as Sagittarius A* is thought to be the location of the supermassive black hole around which our galaxy orbits.

Sagittarius was the most difficult constellation to map so far in my journey through the sky.  It's declination runs from about 12°S to 46°S.  At the latitude in Calgary (~51°N) we can only see to approximately 39°S depending on altitude and topography.  This rendered the southern regions of the constellation forever buried beneath the horizon.  The Summer is the best time to map Sagittarius as it reaches its greatest height above the horizon while the Sun is on the opposite side of the Earth.  This poses additional challenges from 51°N with constant astronomical twilight from the end of May to mid-July.  The Summer also offers a plethora of bugs that can completely destroy an entire night of observing.

I mapped Sagittarius over the course of 3 separate calendar days.  I started late on July 9, 2018 which carried me into the morning of July 10, 2018.  I went out during the evening of July 11, 2018 to a high altitude location with a clear view of the southern horizon.  On this night I was able to find Epsilon, Eta and Theta Sagittarii hovering just a few degrees above the horizon.  Alpha, Beta, Iota and Kappa Sagittarii are permanently below the horizon from Calgary and thus so indicated on the observation record below.

Sagittarius Observation Record

Sagittarius is the 15th largest constellation and it contains many Bayer stars.  It took a long time scaling my observations onto the Powerpoint slide above.

There are several interesting asterisms that can be seen above.  The most famous is the teapot.  The westernmost part of the constellation contains many bright stars in the pattern of a teapot.  Adding to the effect is a lemon wedge on a spoon to the upper left of the teapot.  The Milky Way flows right through the teapot making it look like an enormous amount of steam billowing out.  This is why a spoon is needed, you don't want to get your fingers too close to that steam!

Another asterism, although less famous, is the Terebellum.  The Terebellum is a quadrilateral pattern on the easternmost regions of the constellation.  They are close together in the sky but in reality they are not gravitationally linked at all.

There are many famous deep sky objects found within the boundaries of the constellation.  Fifteen Messier objects call this region of the sky home.  The table below highlights these objects.

Messier	Name/Type
M8	The Lagoon Nebula (Emission Nebula)
M17	The Omega Nebula, The Swan Nebula, The Checkmark Nebula (Emission Nebula)
M18	Open Cluster
M20	The Trifid Nebula (Open Cluster, Emission Nebula, Reflection Nebula, Dark Nebula)
M21	Open Cluster
M22	Globular Cluster
M23	Open Cluster
M24	The Sagittarius Star Cloud (Open Cluster)
M25	Open Cluster
M28	Globular Cluster
M54	Globular Cluster
M55	Globular Cluster
M69	Globular Cluster
M70	Globular Cluster
M75	Globular Cluster

This rich area of the sky is filled with many open clusters and globular clusters.  There are also several notable nebulae that have been viewed over the centuries.  I have viewed the deep sky objects on this list and I can vouch for their beauty.  I will revisit this area of the sky each Summer.

2018 Week 29: (July 15-July 21)

Summer is in full swing and the weather for astronomy has been amazing.  There is no smoke in the air and the clouds have stayed away.  The weather for the upcoming week is looking great!  There are a few things to check out in the sky.  The table below showcases our skies for the week!

Date	Event
July 15	Regulus 1.8°S of Moon
July 15	Venus 1.6°S of Moon
July 19	First Quarter
July 20	Jupiter 4° of Moon

An excellent article written by Nicole Mortillaro highlights the 5 naked eye planets that can be seen in the sky!  Check it out and see if you can spot them all; Mercury is a tough nut to crack sometimes, though.

http://www.cbc.ca/news/technology/5-planets-night-sky-1.4745932

The Moon is beginning another lunar cycle and will be seen as a waxing crescent in the western sky.  It will pair up with Leo's bright star Regulus on Sunday while hanging out with Venus.  It cruises on to its first quarter phase several days later.

The Moon will then appear alongside the largest planet, Jupiter, next Friday.

This raises an interesting point.  If you would like to check out Jupiter, be sure to see it soon.  Jupiter is slowly approaching the western horizon and will soon be soaked in sunshine.  Also, as it gets lower in the sky the atmospheric interference will disrupt the seeing such that it will look like it's boiling!

Saturn is amazing at this time of the year as it stands high in the southern sky at midnight.  There are 11 Messier objects within 8° of our ringed friend.  A telescope will help pull these into view.  Alternatively you could try binoculars.  I was able to see most of them from light polluted suburban skies with a pair just the other night.  The image below highlights these special objects.

Saturn and Friends

Following Saturn is the Greek war god Mars.  The red planet is usually a boring object in the sky, barely shining bright enough to tell it apart from a star.  However, every 28 months Mars reaches what is known as opposition.  The image below illustrates this orbital geometry.  We are fortunate this year that Mars and Earth are extremely close to each other in their elliptical orbits.

Mars Oppositions 2012-2027 (Image Credit: Martin J Powell, www.nakedeyeplanets.com)

The unfortunate news about Mars is there is currently a significant global dust storm.  This storm is shrouding the planet against our peering eyes.  It is nearly impossible to make out any significant features on the surface.  The article below goes into this in more detail.

https://www.skyandtelescope.com/astronomy-news/is-the-mars-opposition-already-over/

The Opportunity rover is currently in safe mode as it is powered by solar and is not getting enough energy.  Curiosity, on the other hand, is powered by radioisotopes and can function seamlessly through storms like this.  Curiosity even took a selfie to commemorate the storm.

Curiosity (Image Credit: NASA/JPL-Caltech/MSSS

I hope you take the time to get outside and enjoy the night sky.  If you plan on leaving the city to go camping, bring along some binoculars and sit under the stars.  The sky is an amazing place full of endless things to observe.

The Milky Way Galaxy

The Milky Way Galaxy is our home.  We live on a planet that orbits a star that, ultimately, orbits our galaxy's center of mass.  There is a black hole residing in the center of our galaxy that is approximately 4 million solar masses.  If you think the Sun is big, imagine 4 million of them packed into the volume of space inside the orbit of Mercury.

What is a galaxy?

According to the Oxford Dictionary, a galaxy is a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

The etymology of the word comes from the Greek word for 'Milky'.  This is a direct reference to the 'milky'-like appearance we can see in the sky from the arms of our own galaxy.

The image below is a map of our own galaxy.  Our Solar System resides on the inside edge of the Orion Spur.  When we look toward the galactic center we are seeing stars from our own spur, stars from the Sagittarius Arm and stars from the Scutum-Centaurus Arm.

Milky Way Map (Image Credit: NASA)

The Orion Spur is quite a minor arm in our galaxy.  It is only 3,500 light years wide and 10,000 long.  When we peer out towards the constellation Sagittarius we are looking toward the galactic center.  If you are in a dark sight you will see this brilliant 'milky' glow of billions of stars.  Also, when we peer out towards the constellation Perseus we will see the stars from that arm.

Below are some quick facts about The Milky Way:

Characteristic	Value
Type	Barred Spiral
Diameter	100,000-180,000 Light Years
Mass	800 Billion - 1.5 Trillion Solar Masses
Number of Stars	100-400 Billion
Cosmic Year	240 Million Years

Our galaxy has a mass of more than a trillion Suns.  This is incredible.  Our Sun revolves around the Milky Way's black hole every 240 million years.

It would take light more than 100,000 years to traverse the entire diameter of our galaxy.  Living on Earth with most distances measured in kilometers or miles, it is difficult to conceive the enormity of our galaxy.  This would translate into nearly a quintillion kilometers!

There are interesting things to view in each of the arms in the region near us.  Our home Orion Spur contains amazing sights such as the Orion Nebula, Dumbbell Nebula, The Pleiades and the Beehive Cluster.

If we were to examine objects in the Sagittarius Arm we would see such things as the Eagle Nebula, Omega (Swan) Nebula, and the Sagittarius Star Cloud.

Looking toward the anti-galactic center in the Perseus Arm we could see the Crab Nebula and many Open Clusters such as M36, M37 and M38 within Auriga.

The image below shows an inverted map of the galaxy with the constellations listed.  As you can see, relative to Earth, Sagittarius is directly in line with the Galactic Centre while Auriga is toward the anti-center.

Milky Way Constellations

The Milky Way is just one of billions (possibly more than a trillion) galaxies found throughout the Universe.  We can see other galaxies in our night sky with sometimes no more than our own eyes.  The Magellanic Clouds are satellite galaxies to our own and can be seen in the southern hemisphere skies.  For those living in Northern climes, the Andromeda Galaxy can be seen outside of the urban shine.  At 2.5 million light years away it is the closest major galaxy to our own.  At some point in the far distant future (~4 billion years) it will collide with our own causing a galactic merger.

All of the stars you can see in our night sky call the Milky Way their home.  If you can make your way to a dark site be sure to enjoy the view of the milky arms that form our galaxy.