# Dust - The Always-Nuisance Dust is quite the nuisance wherever we go, it seems! From causing allergies to obscuring views, thewd spectre of dust always seems to follow us around. Not even astronomers are impervious to this. Sometimes, space throws us curveballs, and those curveballs often come in the form of large dust clouds, drifting across the galaxy much like our sun. Typically, *anything light-absorbent enough to obscure light* can be considered as 'dust'. They do make cool nebulae though. Just look at the [Horsehead](https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_s_view_of_the_Horsehead_Nebula)! ![[Pasted image 20240106155404.png]] *The Horsehead Nebula, made of interstellar dust. Credit: ESA/Euclid* # Dust-Induced Reddening Remember - [[Blackbody Radiation (Thermodynamics)#Blackbody Radiation - Planck's Odyssey|stars emit as a spectrum]]. This means that there is not set wavelength for a star to glow in. Like our atmosphere, dust allows for significant [[Rayleigh Scattering (Waves)|rayleigh scattering,]] meaning that blue light is scattered in different directions while red light is allowed through this great cosmic filter. [^1] Here's a handy diagram, as per usual! ![[Pasted image 20240106162510.png]] Most telescopes have what we call a [[Space Telescope Conventions (Astro)|B-V Filter]] - a generic, high-energy blue light filter that allows for more broad measurement-taking. Using data from this specific filter, we can get the magnitude of the base extinction: $B V_{intrinsic} - B V_{observed} = E_{B V}$ *Where:* - $BV_{observed}$ is the observed magnitude from the filter - $BV_{intrinsic}$ is the intrinsic luminosity of the object - $E_{BV}$ is the loss of blue light due to cosmic extinction >[!Success]- Cosmic Extinction Limits >Cosmic extinction can happen at almost any distance - provided that there's enough dust separating us from a distant object, we don't even need one of the dusty clouds that drift across the milky way for dust extinction! > >However, note that [[Redshift & the Doppler Effect (Astro)|redshift]] can also play a role for very, very distant objects. This means that we've got an effective range for this formula. > >**Question:** What do you think is the *maximum distance* for this formula? How would you reconcile it with redshift, besides? [^1]: Otherwise known as [[Rayleigh Scattering (Waves)|Rayleigh Scattering.]] Have fun! # A Case Study - The Cygnus Rift Our Milky Way is a huge galaxy. Stretching almost 200,000 light years across, this big behemoth of stars and gas has much to offer. However, if we look at the constellation of [Cygnus](https://www.britannica.com/place/Cygnus-constellation), there's this big band of dust blocking our view towards its center. While this place is a prime target for infrared astronomy, pretend you haven't brought your thermometer with you today. Let's brush away the thorns of the region to unlock the secrets of its El Dorado! ![[Pasted image 20240107010236.png]] *Gaia's All-Sky survey image! Credit: ESA/Gaia/DPAC* Past the gas and dust lies a cluster - one of the most massive, prolific OBA clusters to date. Welcome, to the Cygnus OB2 Association! ![[Pasted image 20240107010428.png]] *The Cygnus OB2 Association - composite with X-Rays, H-alpha, infrared. Credit: NASA/CXC/SAO/J. Drake et al; H-alpha: Univ. of Hertfordshire/INT/IPHAS; Infrared: NASA/JPL-Caltech/Spitzer.* Herein lies several dozen OB stars - blue stars which glow with hundreds and even thousands of solar brightnesses, with several stars even eclipsing Rigel's brightness. Even given their distances, these stars should be shining back at us, no? All this gas and dust in front of it, however, has proven to be nuisance - only the longest, red wavelengths are let through, whereas the high-frequency waves, which those stars are brightest in, are scattered, fading into the rest of the galaxy. As a result, this cluster stands at an apparent magnitude of 7 - visible with most telescopes. If it weren't for this gas, many of these stars could shine at constant magnitudes of upwards of 2, a brightness increase of almost 100 times. Dust - it truly does get everywhere, does it? *If you're curious on how the Cygnus OB2 image was created, feel free to take a look at our image processing section!* [[Processing Photos - A Basic Rundown]] # Links (Further Reading) Have fun! Working around interstellar gas is a hot topic in astronomy these days. https://www.sciencedirect.com/topics/physics-and-astronomy/interstellar-dust # Navigation Go back to the main menu here: [[Everything Astronomy]]