## part 1 Images of the Universe #### 1.1.1 Measuring brightness Using photometric apertures on images to measure total brightness of an object. typical result for Star and galaxy: ![[../Assets/Pasted image 20231206193835.png|400]] The [[../Glossary/pointspread function]] is the way the light of a star is spread across multiple pixels. For sources whose true angular size is larger than a single image pixel, such as the galaxy in Figure 1.3b, the radial brightness profile is broader than the PSF, and follows a characteristic shape based on the distribution of stars. #### 1.1.2 Measuring sizes The telescopes [[../Glossary/pixel scale]] is the conversion factor between pixels and the angular size or separation in arcsec or arcmin. my scope a 13.2 cm refractor has a pixel scale of 0.84" or 0.014 arcmin per pixel in primary focus. With reducer of 0.7 it becomes 1.2" or 0.02 arcmin per pixel. then if distance is known: *Diameter (D) = sin $\Phi$ x distance* {phi in radians, small angle if angle < 0.2 rad} #### 1.1.3 Measuring shapes We are recording three dimensional objects in a two dimensional frame For a circular disc-like object, the observed major axis (i.e. twice the semimajor axis) corresponds to the true diameter of the disc, and the inclination angle (tilt, ) relative to the plane of the sky is given by *Equation $\Phi$ = cos$^{-1}$ ($\dfrac{b}{a}$) {with a = semis-major and b= semi-minor axis} * where is the measured semimajor axis and the measured semiminor axis. If a linear object is projected at an angle of to the plane of the sky, then its true length, , is related to its measured length, , *by L= $\dfrac{l}{cos\Phi}$* #### 1.2 Structure in images #### 1.2.2 Exploring the Messier catalogue upload to forum and make screenshots. #### 1.2.3 Types of extended objects There are five main types of extended astronomical object in visible light images: open clusters, globular clusters, galaxies, [[../Glossary/planetary nebula]] and diffuse nebulae. #### 1.3 Colour in astronomy images #### 1.3.1-1.3.3 images, Narrow-, broadband and multi-wavelength - Astronomical images taken with different telescope filters, spanning different wavelength ranges, can be combined to produce colour images. Quantitative measurements, such as colour index, are usually made by carrying out photometry separately on images from individual filters and then combining the measurements. - Narrowband images can be made using filters that allow through only light associated with a particular emission line. One of the most commonly used examples is Hα, which highlights the locations of regions of hot gas. - Images are also made across the electromagnetic spectrum. Multi-wavelength astronomy involves using images spanning a wide range in wavelength, from radio waves to gamma rays, which highlight different regions and features. #### 1.4 Mapping the sky Cosmic Web consists of galaxy clusters connected by filaments. In between are void regions with far fewer galaxies. (fig 1.15) ![[../Assets/Pasted image 20231216150328.png|300]] [[../Glossary/time-domain survey]] is a survey that images the same area of sky many times to look for changes. ## Part 2 Organising and classifying #### 2.1 Milky Way ingredients and structure - Stars and star clusters - Star forming regions and stellar debris - molecular gas - SNR's - Interstellar medium (ISM) gas and dust. - 70% H2 and 28% He - Molecular clouds densest regions with *T<50 K*, Mainly H2 with CO. - CO is more easily observed via strong radio emission lines - ![[../Assets/Pasted image 20231216163405.png]] - at *T> 50 K* the (mainly hydrogen) gas in the ISM is in atoms iso molecules. H is then referred to as HI eg 21cm radio emission - At *high temperatures* the atoms become ionised. HI becomes HII (H2, though not the molecule). These area's are luminous (H$\alpha$ ) and are associated with star forming regions. - [[../Glossary/dust]] is only tiny portion of mass of the milky way. Check link to read about its constituents. gives rise to the reddening of the light of stars. #### 2.2 Beyond the Milky Way - **Galaxy Zoo**: A citizen science project aimed at classifying galaxies. - **Hubble's Tuning Fork**: A classification system that organizes galaxies based on their appearance. It includes spiral (S), elliptical (E), lenticular (S0), and irregular (Irr) galaxies. - **Spiral Galaxies**: Characterized by most of their stars being in a flattened disc, with a central bulge and a surrounding halo of stellar and dark matter. Their features include: - *Central Bar*: Some spiral galaxies have a central bar structure, while others do not. This characteristic differentiates between SB (barred spirals) and S (non-barred spirals) categories. - *Subtypes - Sa, Sb, Sc*: These classifications are based on the appearance of the spiral arms and the size of the central bulge. Sa galaxies have tightly wound arms and large bulges, Sc galaxies have more loosely wound arms and smaller bulges, and Sb galaxies are intermediate. - *Orbital Speed*: The orbital speed of stars in a spiral galaxy is described by the formula $v(r) = \sqrt{\dfrac{GM(r)}{R}}$ {where v(r) is the speed at a radius R, G is the gravitational constant, and M(r) is the mass within that radius.} *Formation of Spiral Arms*: The spiral arms in galaxies are regions of active star formation, appearing due to the differential rotation of the galaxy's disc. The shape and persistence of these arms are influenced by various factors including gravitational disturbances from nearby galaxies and waves of star formation. - **Elliptical galaxies** - Appear as smooth, spheroidal clouds of stars without structural features like spiral arms, similar in appearance to the bulge of a spiral galaxy. - Typically redder in color than spiral galaxies, indicating populations of older stars and a less active phase of star formation. - Contain smaller quantities of gas and dust than spiral galaxies. - Classified by their ellipticity, calculated as \( f = 1 - $\frac{b}{a}$), with subcategories ranging from E0 to E7 based on this measurement. - Kinetic energy within elliptical galaxies is predominantly in random motion, making velocity dispersion a key observable quantity. - Spectral signatures, broadened by the Doppler effect, allow for the measurement of velocity dispersion. - *Mass estimation* is facilitated by the [[../Glossary/virial theorem]], which relates kinetic energy (\( E_k \)) to gravitational potential energy (\( E_g \)).: $E_k = - \frac{1}{2} E_g$ - The *gravitational potential energy* is given by the formula: $E_g = - \frac{GM^2}{R}$ - This results in: $\Delta v^2 \sim \frac{GM}{R}$ - **Other types ** - [[../Glossary/irregular galaxies]] - Smaller than E or S types - Contain more gas and dust so more star formation: bluer than E type - [[../Glossary/lenticular galaxies]] - kind of disc - The S0 and SB0 galaxies located between the E and S galaxies - similar structure as spiral - no spiral structure - **Galaxy collisions** - [[../Glossary/Merging galaxies]] give rise to irregular galaxies #### 2.3 The distant Universe **Finding distant galaxies** - There are two importent methods for identifying faint redshifted galaxies other than spectroscopy. - [[../Glossary/The dropout technique]] in which the most distant galaxies are seen to be present in certain telescope filters and absent from others, due to the effect of particular wavelengths of light being absorbed by intervening material - [[../Glossary/gravitational lensing]], in which light from distant galaxies can be amplified due to its path being bent by intervening galaxies or galaxy clusters. - Distant galaxies are, on average, smaller than the nearby older galaxies. They are also bluer which points to more active star forming. Also their structure is mostly irregular where as the nearby older galaxies have spiral structures and central bulges. ## Part 3 The hidden Universe #### 3.2.1 The hidden cold and dusty universe [[../Glossary/dust]] is a very important constituent of space. Not only because it scatters and absorbs EM radiation but also because it plays an important role in the lives of galaxies and stars. The mid - and [[../Glossary/far-infrared]] observation can see inside the dust. Observations of dust, both via its absorption in the optical part of the spectrum, and its emission at far-infrared, sub-millimetre and millimetre wavelengths (sub-millimetre and [[../Glossary/millimetre astronomy]] involve observing emission in the region between the far-infrared and radio part of the spectrum), have taught us about its importance for star and planet formation. The development of IR astronomy led to the discovery of [[../Glossary/sub-millimetre galaxies]]. #### 3.2.2 The hidden hot Universe The hottest regions are best studied using [[../Glossary/X-ray astronomy]], which must also be done from above the atmosphere. X-ray astronomy has revealed hot regions including young stars, [[../Glossary/X-ray binary]] star systems in which a neutron star or black hole pulls matter off a companion and heats it, and the hot [[../Glossary/intracluster medium]]– a diffuse gas in which galaxies are embedded #### 3.2.3 The hidden energetic Universe Energetic parts of the Universe can also be studied via radio astronomy. Most bright radio sources produce [[../Glossary/non-thermal radiation]], via the synchrotron process in which energetic particles spiral in magnetic fields. Radio astronomy reveals exotic phenomena associated with black holes in distant galaxies: the [[../Glossary/quasar]]s and [[../Glossary/radio galaxies]] with large-scale jets. Supernova remnants and [[../Glossary/pulsars]] – rapidly rotating neutron stars – are also important components of the radio sky whose existence would be missed if we only had visible observations. ![[../Assets/Pasted image 20231231145135.png|300]] ## reference [[Astronomy]] [[../Supporting info/LaTex|LaTex]] [[../TMA 3]] [[../Glossary/Doppler broadening]] [[../constants & formula's|constants & formula's]] [[../Glossary/The EM spectrum]]