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Stargazing Basics 2: Understanding star magnitude in astronomy


Hi I’m David Fuller from the “Eyes on
the Sky” video series. Let’s look at another aspects of Stargazing Basics, this time, magnitudes
of various objects. Magnitude is just a fancy way to describe
the difference in brightness of objects we see in the night sky. And it’s not too hard
to learn how it works, but let’s start with some history. The Greek astronomer Hipparchus
developed the magnitude scale back in the 2-nd century BC, when he assigned the brightest
stars a magnitude of “one” and the dimmest stars that of “six,” the in-between stars
of 2, 3 , 4 and 5 magnitude assigned according to brightness. He assumed that the difference
in brightness of stars was 2.512 times brighter than the next dimmest one. Taken across that
full 6 magnitude scale, this meant that the brightest stars – the first magnitude ones
– were 100 times brighter than the dimmest, 6-th magnitude ones. It also allows for a
fairly easy way to determine other brightness differences: The difference from first to
third magnitude is 6.3 times; first to fourth, 15.8, first to fifth , about 40 times. This worked just fine until Galileo turned
a telescope towards the heavens, and humans discovered there were a LOT more stars out
there than just the first through sixth magnitude ones they could see naked eye. But what they
did was just extrapolate the scale further. So much like golf or ERA in baseball, the
lower the number, the brighter the star, and the higher the number, the dimmer the star.
11-th magnitude is 100 times dimmer than 6-th magnitude, and that 11-th magnitude star would
also be 10,000 times dimmer than a first magnitude star. In the other direction, we have some objects
that are brighter than first magnitude stars. Hipparchus actually fudged the numbers a bit;
the star Sirius in the winter sky is definitely brighter than most other bright stars, and
it shines at magnitude negative one point four. The planet Jupiter is brighter than
that, often appearing at around magnitude negative 2, and Venus brighter still, typically
around negative four. When objects are bright, they are denoted on star charts with larger
dots; dimmer stars are usually given smaller dots. This helps us locate brighter objects
in the sky more easily. But beyond the stars’ magnitudes is that
of the Moon and Sun. The full Moon in the night sky shines at magnitude negative 12.7,
and the Sun at magnitude negative 26.7! Those are both bright compared to starlight, but
also a huge difference, even between themselves, as the Sun is 400,000 times brighter than
the full Moon! Now everything we have discussed has been
“visual magnitude,” meaning how bright or dim objects appear to our location on Earth.
Another concept is “absolute magnitude,” used by astronomers to compare the relative
brightness of objects when placed the same distance. But that is more complex than what
we need to know for simple stargazing purposes. However, for visual magnitude, it helps to
understand how it relates to other objects besides stars. Stars are point-like objects
in the sky, so it is easy to assess their magnitude and brightness. But galaxies, star
clusters and nebula are not quite as easy. So we look at their “integrated magnitude.”
That’s a way of saying that the same magnitude is now spread out over a larger area. For
small objects, that can mean it is something that will look brighter to us in telescopes.
If the area if very large though – such as the galaxy M33 or the nebula M1, those
objects may look very dim, relatively speaking. If possible, try to look for the surface brightness
of an object; objects above a surface brightness of 11 or 12 can be very difficult to find
from light polluted areas. That’s a quick overview of the magnitude
scale, and how to understand it. Just remember the Sun and Moon have negative magnitudes
and are the brightest visual magnitude objects, and lower numbers are dimmer stars and objects,
and you’ll be in good shape! In the next video, I’ll explain how to easily measure
distance in the sky, moving FROM bright objects to the dimmer ones, so we can better utilize
optical aids like binoculars and telescopes to find interesting objects. Thanks for watching;
I’m David Fuller. Keep your eyes on the sky and your outdoor lights aimed down by
using dark sky friendly lighting fixtures, so we can all see, what’s up.

36
Comments
  • Thanks so much! I had homework for star magnitude and these facts helped me get it done real quick and helped me understand alot about the topic!

  • Man I'm getting interested in stargazing and astronomy right in a cloudy week. Oh and it's also new moon, which is great. NOT 🙂

  • Only 23k followers from great videos about an AMAZING subject + Kardashians getting most peoples attention = humans are brain washed

  • My only words of advice would be to put an annotation at 4:45 for the audio edit. The caption reads "lower" as well. Unfortunately not all phones show all annotations. I'm watching this on a PC, but my phone displays some annotations on youtube, but not others. I'm not sure what determines it.

  • when star A has M= -2 and star B has M= 3, I know star B is brighter, but by how much? Do I multiply 2.5 between magnitude steps?

  • Hi EOTS! I JUST CAME UPON YOUR CHANNEL TODAY. I WANT TO DO GAZING. I NEVER USED TO LOOK UP AND WHERE I LIVE IS ALWAYS CLOUDY, ETC. I WANT TO DISCOVER! YOU'RE VERY TALENTED AND I LIKE YOUR VIDEO EDITING SKILLS. TAKE CARE AND CAN'T WAIT TO SEE MORE.

  • What about it information is best for watch long distance star and how many long we watch the star?

    Product Description

    Brand: Bresser
    Type: Reflector
    Diameter: 114 mm
    Focal Length: 900 mm
    Description:
    Galaxia 114/900 EQ-reflector
    Its large mirror diameter allows for excellent light collection. The eyepiece holder with one of two included eyepieces is attached to the side of the telescope tube and allows for easy viewing. The top quality equatorial mount adds to the professionalism of this telescope and lets the user perfectly align the telescope with the viewing object. Explore the planets within our solar system and discover new worlds. The included astro software lets you compare what you see on your monitor with the night sky. An excellent learning and discovery tool. The superiority of this telescope can be complimented with the numerous optionally available accessories from BRESSER.
    Technical Specifications and Features:
    Produce-No.46-14900Article NameGalaxiaOptical DesignNewtonian ReflectorMagnification36x-675xFront Lens Ø (Clear Aperture)114 mmFocal Length, Focal Ratio900 mmStandard Eyepiece(s)K-25 mm, K-9, K-4 (31,7 mm)Magnification with eyepiece36x, 100x and 225x3x Barlow lensK-25 mm : 108xK-9 mm : 300xK-4 mm : 675×1.5x Erecting Lens54x, 150x, 337.5xTelescope Shipping Weight (w/tripod)11,70 kgMaterialslacquered, anthraciteTelescope MountingEquatorial EQ2Telescope TripodSteel TripodAccepts Eyepiece Barrel Ø31.7 mmResolving Power in arc seconds1Limiting Visual Stellar Magnitude (approx.)12.9Recommended Maximum visual power228View Finder ScopeLED ViewfinderFilterMoon filterShipping carton weight17 KgShipping carton dimension108 x 47 x 25 cm3
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  • What is 11.1 magnitude in sky? Plz answer i am in confusing how many distance and it's focal length+diameter this is best?

  • Don’t know if you read comments anymore but thanks for this series. Short, to the point, and understandable. My compliments for a YouTube series above the norm.

  • How did you figure out that the sun is 400K times brighter than the moon? Can I get a formula?

  • This was a nice refresher. I hadn't heard of Integrated Brightness before, so that was great. I really like your audio edit with the lower/higher near the end. It's genuine, and I get it. Thanks.

  • My dog has a magnitude of just under that of the moon ,….(white german sheperd)..
    But then again, my girlfriend just showed me that her ass has a magnitude of just over that of the moon…nice :^)

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