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!