Results 1 to 8 of 8

Thread: Object of the Week, December 28, 2015 - Messier 1, the Crab Nebula

  1. #1
    Member Howard B's Avatar
    Join Date
    Feb 2012
    Location
    Scappoose, Oregon USA
    Posts
    569

    Object of the Week, December 28, 2015 - Messier 1, the Crab Nebula

    1024px-Crab_Nebula.jpg

    "What caused me to undertake the catalog was the nebula I discovered above the southern horn of Taurus on September 12, 1758, whilst observing the comet of that year. This nebula had such a resemblance to a comet in its form and brightness that I endeavored to find others, so that astronomers would no more confuse these same nebulae with comets just beginning to appear. I observed further with suitable refractors for the discovery of comets, and this is the purpose I had in mind in compiling the catalog.
    After me, the celebrated Herschel published a catalog of 2000 which he has observed. This unveiling of the heavens, made with instruments of great aperture, does not help in the perusal of the sky for faint comets. Thus my object is different from his, and I need only nebulae visible in a telescope of two feet [focal length].”

    Charles Messier

    Although Messier found M1 in 1758 it had actually been discovered 27 years earlier by an English physician and amateur astronomer, John Bevis, and it wasn’t until 1771 that Messier became aware of the priority of Bevis’ discovery.

    Interestingly, it seems he came across M1 on August 28, but measured its position on September 12th, which he regarded as its discovery date.

    Messier’s terse description of what he saw doesn’t give a novice observer much to go on:
    “Nebula above the southern horn of Taurus, it doesn't contain any star; it is a whitish light, elongated in the shape of a flame of a candle, discovered while observing the comet of 1758.”

    But what an amazing object M1 turned out to be – the only supernova remnant in his catalog and one of the most intensely studied objects in the sky for the past 90 years.

    Physical Properties
    The supernova left behind M1’s expanding nebulosity and a fast spinning neutron star at its center. Spinning almost exactly 30 times per second, this 1.4 to 2.0 solar mass object is only about 18 miles in diameter. Its powerful magnetic field focuses its electromagnetic radiation into narrow beams, which happen to be directed toward Earth.

    The neutron star is very gradually slowing its spin, a process that puts out 75,000 times the energy of our sun, and powers the synchrotron radiation that makes the main body of M1’s nebulosity glow. Synchrotron radiation is produced by electrons curving their way through a strong magnetic field at up to half the speed of light.

    This extreme energy produces an astronomically wild place in the central area of M1. The pulsars equatorial wind slams into the nebula and forms a shock front that changes shape daily.

    The filaments are likely the remains of the progenitor star’s atmosphere and are composed of ionized helium and hydrogen with carbon, oxygen, nitrogen, iron, neon and sulfur mixed in.

    M1 is approximately 6300 light years away, and since its explosion has expanded to about 13 light years along its greatest length.

    Visual Observations
    Messier didn’t make a sketch of his first nebula, but many 19th century astronomers did. As was too often the case, sketches of the same object bore little resemblance to each other, sparking a lively debate on their scientific usefulness. The German astronomer Wilhelm Tempel complied a few of the more prominent sketches of M1 to make his point that a standardized methodology needed to be followed when making astronomical drawings. It’s a fascinating example of what 19th century astronomy was faced with until the invention of practical astrophotography. Clockwise from top left the sketches were made by Tempel, John Herschel, Heinrich d’Arrest, William Lassell, Pietro Secchi, and Lord Rosse. Yes, these sketches are all of M1.

    M1_TempelComparison.jpg

    By the way, it was Lord Rosse who gave M1 its Crab Nebula nickname when he discovered its filaments in 1844. His 1855 “bumblebee” sketch is shown above (center left) but his first drawing looked much like Secchi’s in the lower left corner.

    Into this mix I’ll toss two sketches I made in early December, 2011. I sketched M1 without filters and then with an OIII filter to show how the appearance of the nebula changes.

    Without a filter the nebula has a broad, soft “S” shape that gently feathers along both ends. The central area is brightest and with a 16 inch or larger scope the 16th magnitude pulsar can be seen when the seeing is steady under a dark sky. A star just slightly brighter than pulsar, but not associated with it, forms an optical double with the pulsar and both can be seen near the center of the nebula. The pulsar is the slightly dimmer of the two.

    The overall scene at 253x through my 28 inch scope is quite nice as M1 sits in a lovely star field that compliments its soft nebulosity.

    M1 double sketch.jpg M1 double sketch_inverted.jpg

    With the OIII filter in place the nebula takes on a very different appearance. Now strongly oval in shape, several of the famous filaments appear, with the two brightest being quite easy to see. I’ve seen vague hints of other filaments but not enough to mark them on my sketch. However, the entire nebula has a mottled look and the perimeter of the nebula has a feathered appearance. Filaments have been detected with 12 inch scopes, so a huge instrument isn’t needed to get a good view.

    But a really big scope comes in handy if you want to see the pulsar in action. A few years ago Dan Gray (Sidereal Technology) made a rotating shutter especially to “blink” M1’s pulsar. He set the rotation speed just slightly off from the rotational speed of the pulsar so its image would slowly fade and brighten over about 15 seconds. Attempts with our respective 28 inch scopes failed, but he met with success with 60 inch and 90 inch professional scopes in Arizona. I was part of the observing group that saw the pulsar dim and brighten using Dan’s shutter when hooked up to the Bok 90 inch scope at Kitt Peak, and that experience ranks as one of my top observing highlights.

    M1_neutronstarrotation.jpg M1_neutronstarrotation_inverted.jpg

    All Messier knew in 1758 was that he hadn’t found a comet. Fortunately M1 turned out to be one of the most intriguing astrophysical objects in the sky that’s easily accessible to amateur telescopes.

    Let us know - you've already given this one a go!
    Howard
    30-inch f/2.7 alt-az Newtonian
    https://sites.google.com/site/howardbanichhomepage/
    https://sites.google.com/site/sprays...pemirrors/home
    Contributing Editor, Sky & Telescope magazine

  2. #2
    Member
    Join Date
    Feb 2012
    Location
    Germany
    Posts
    812
    Hi Howard,

    very nice OOTW. I did not know the sketching compilation from temple but indeed very interesting because of the different interpretation. Thanks for showing this historical document.
    Just last month a took a visit with the 8" telescope and was pleased by the bright and nice form of the SNR. Nice view also in smaller apertures.

    I need several observations year after year until the conditions were good enough to try a sketch with the 27". Seeing and transparency were very good on the High Alpine sky (Edelweißspitze 8400ft). I tested a lot with filters and exit pupils to reach the sweet spot which was very small to see all the filaments.
    27", 366x, [OIII] (Astronomik), Seeing II, NELM 7m+
    M1.jpg

    I also tried to split the "double star" to see the fainter pulsar star last years. I had never success with my 16" but the 20" showed it barely when conditions were perfect enough. With the 27" it was always an easy task and when condition were good the double were seen with space between both peaks.

    I never heard about such an experiment with a shutter. Very cool. Do you only use an easy time shutter Howard to affect a short period of the lower brightness of the pulsar? Nothing to do with a polarization?
    Last edited by Uwe Glahn; December 29th, 2015 at 07:57 PM. Reason: attachment repair
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  3. #3
    Co-Founder DSF.com Jimi Lowrey's Avatar
    Join Date
    Feb 2012
    Location
    Fort Davis Texas
    Posts
    569
    Good job Howard!

    Has anyone seen the jet in the crab nebula? I did not know about it till recently and have never looked for it.

    M1-with jet.jpg

    I am anxious to try it.

    Crab Nebula Jet.jpg
    Clear Skies,

    Jimi Lowrey
    Fort Davis Texas

    48"F4 OMI/TEC
    28'F4 ATM

  4. #4
    Member Howard B's Avatar
    Join Date
    Feb 2012
    Location
    Scappoose, Oregon USA
    Posts
    569
    Hi Uwe, I've only used Dan Gray's shutter to see the pulsar blink, I've never tried polarized filters.

    Hey Jimi, I hadn't heard of the jet either, so something new to look for!
    Howard
    30-inch f/2.7 alt-az Newtonian
    https://sites.google.com/site/howardbanichhomepage/
    https://sites.google.com/site/sprays...pemirrors/home
    Contributing Editor, Sky & Telescope magazine

  5. #5
    Member
    Join Date
    Feb 2012
    Location
    Germany
    Posts
    812
    I just came back from outside and I think I got the jet.
    Conditions were extremely good (fog in the valleys, M33 steadily direct vision, bright zodiacal band). I used the 27" with 172x + [OIII] and could detect some very faint nebula between the three stars which looks out the nebula at the jet position. The stars are also the problem. Although I could not detect any brightening between the stars without filter and the nebula with filter stays stationary when I wobble and move the telescope I'm not pretty sure if it was the jet or the filter effect because of the 13mag stars. I tend to the nebula.
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  6. #6
    Member hajuem's Avatar
    Join Date
    Jul 2012
    Location
    Stafflangen, Germany
    Posts
    66
    Hi
    Thanks for excellent description, Howard

    That with the jet from M 1 is new to me !! Thanks for the info!!
    It was for best conditions and large telescopes
    My sketch with 16":
    M 1 Original neg.jpgM 1 Original.jpg

    CS Hajü
    www.astromerk.de

  7. #7
    Member akarsh's Avatar
    Join Date
    Nov 2013
    Location
    Sunnyvale, CA
    Posts
    376
    Wow, I'm looking at this OOTW only now, which I consider a wonderful synthesis. I haven't looked carefully at the object in a long while, and considering that observing skill grows, it's worth revisiting. Uwe, it's encouraging to know you could see the jet! The history of the object is very interesting (esp. the Tempel sketch collection!) as is the shutter experiment to visually track the variation of the pulsar!!

    Clear Skies

    Regards
    Akarsh
    18" f/4.5 Obsession dob "Romela"
    6" SkyQuest Orion dob
    Garrett Optical 25x100
    Homepage
    DSS Tool : Logbook Project : KStars
    The Astronomy Connection : Austin Astronomical Society : Bangalore Astronomical Society

  8. #8
    Co-Founder DSF.com Jimi Lowrey's Avatar
    Join Date
    Feb 2012
    Location
    Fort Davis Texas
    Posts
    569
    I had a positive observation of the jet. It was not as hard to see as I thought it would. I used a O III filter which got a good response at 287X. There is a brighter patch just the other side of the two stars that was the easiest to see with AV.
    Clear Skies,

    Jimi Lowrey
    Fort Davis Texas

    48"F4 OMI/TEC
    28'F4 ATM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •