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- Telescopes are devices used to observe distant stars, galaxies, and other objects by magnifying them. Telescopes come in different types depending on the wavelength of light they observe, such as optical, radio, infrared, ultraviolet, X-ray, and more. - Larger telescopes provide higher sensitivity, allowing fainter objects to be observed, and higher resolution, allowing smaller structures to be resolved. However, limitations in size exist due to technical and financial constraints. - Radio interferometers overcome size limitations by combining signals from multiple antennas spaced far apart, effectively creating a telescope as large as the spacing between antennas. This allows for much higher resolution than a single radio dish telescope.
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lecture9&10
- 1. Introduction to modern astronomy 9&10 島袋隼⼠(Hayato Shimabukuro)（云南⼤学、 SWIFAR） ©GETTYIMAGES
- 3. What is telescope? •Telescopes is device to observe distant stars, galaxies and so on by magnifying them. •You can use the telescope to observe stars and galaxies at home. •The telescopes which are used in astronomy are more powerful, high specification, and large. •We observe electromagnetic waves from the universe through telescopes
- 8. •Remember electromagnetic waves. Depending on their wavelengths, the electromagnetic waves have different names. Electromagnetic waves
- 9. I(ν, T) = 2hν3 c2 1 ehν/kT − 1 The blackbody spectrum F = σT4 [W/m2] •Remember Blackbody spectrum (Planck spectrum) Total energy If we measure energy from stars and galaxies by electromagnetic wave, we can estimate their temperature.
- 10. Universe by multi-wavelength •If we use different wavelength telescopes, our universe seems to be different.
- 11. •If we see a galaxy by radio wavelength, we can see cold gas inside the galaxy (~600K) Universe by multi-wavelength
- 12. •If we see a galaxy by radio wavelength, we can see cold gas inside the galaxy (~600K) Universe by multi-wavelength
- 13. •If we see a galaxy by infrared and optical wavelengths, we can see stars inside the galaxy (~4500-6000K) Universe by multi-wavelength
- 14. •If we see a galaxy by infrared and optical wavelengths, we can see stars inside the galaxy (~4500-6000K) Universe by multi-wavelength
- 15. •If we see galaxies by ultraviolet wavelength, we can see hot stars inside galaxies (~10,000K) Universe by multi-wavelength
- 16. •If we see galaxies by ultraviolet wavelength, we can see hot stars inside galaxies (~10,000K) Universe by multi-wavelength
- 17. •If we see galaxies by X-ray wavelength, we can see hot gas inside the galaxy (~ K) 107 Universe by multi-wavelength
- 18. •If we see galaxies by X-ray wavelength, we can see hot gas inside the galaxy (~ K) 107 Universe by multi-wavelength
- 19. Universe by different wavelength The Milky Way galaxy seen by multi-wavelength
- 20. A kind of telescope •There are various kinds of telescope corresponding to wavelength.
- 21. A kind of telescope •There are various kinds of telescope corresponding to wavelength. Subaru telescope •Optical and infrared wavelengths
- 22. A kind of telescope •There are various kinds of telescope corresponding to wavelength. Subaru telescope •Optical and infrared wavelengths ALMA telescope •Radio wavelength
- 23. A kind of telescope •There are various kinds of telescope corresponding to wavelength. Subaru telescope •Optical and infrared wavelengths ALMA telescope •Radio wavelength Chandra satellite •X-ray wavelength
- 24. Telescopes in China •China has its own telescope projects.
- 25. Telescopes in China •There are some big telescope projects. CSST(巡天) FAST •Radio wavelength •UV-optical wavelengths 500m!
- 26. Telescopes at Yunnan •Yunnan University (SWIFAR) leads “Mephisto” telescope •Yunnan observatory has 40 m radio telescope
- 27. Optical telescope •Optical telescopes(光学望远镜) are designed to collect the visible light that human can see. •The history of optical telescope has a long history, back to the days of Galileo in the 17th century. Galileo
- 28. Optical telescope •The light is reflected by flat mirror. •If the angle of incident light is large, the deflection angle is also large. On the other hand, if the angle of incident light is small, the deflection angle is also small. •On the other hand, curved mirrors focus on a single point all rays of light arriving parallel to the mirror.
- 29. Optical telescope •The light is reflected by flat mirror. •If the angle of incident light is large, the deflection angle is also large. On the other hand, if the angle of incident light is small, the deflection angle is also small. •On the other hand, curved mirrors focus on a single point all rays of light arriving parallel to the mirror.
- 30. Optical telescope •The light is reflected by flat mirror. •If the angle of incident light is large, the deflection angle is also large. On the other hand, if the angle of incident light is small, the deflection angle is also small. •On the other hand, curved mirrors focus on a single point all rays of light arriving parallel to the mirror.
- 31. Optical telescope •The light is reflected by flat mirror. •If the angle of incident light is large, the deflection angle is also large. On the other hand, if the angle of incident light is small, the deflection angle is also small. •On the other hand, curved mirrors focus on a single point all rays of light arriving parallel to the mirror.
- 32. Optical telescope •The light is reflected by flat mirror. •If the angle of incident light is large, the deflection angle is also large. On the other hand, if the angle of incident light is small, the deflection angle is also small. •On the other hand, curved mirrors focus on a single point all rays of light arriving parallel to the mirror.
- 33. Optical telescope •There are various kind type of optical telescope
- 34. Optical telescope •There are various kind type of optical telescope
- 37. Optical telescope •For example, Keck telescope (and Subaru telescope) is Cassegrain type telescope
- 38. Breaktime
- 39. Optical telescope •The important properties of the telescope are sensitivityand resolution Sensitivity(聚光能⼒) : How fainter images we can observe The sensitivity depends on the collecting area. A larger diameter telescope has more sensitivity. ＜ This telescope can observe fainter objects.
- 40. Optical telescope •The important properties of the telescope are sensitivityand resolution Sensitivity(聚光能⼒) : How fainter images we can observe The sensitivity depends on the collecting area. A larger diameter telescope has more sensitivity. ＜ This telescope can observe fainter objects.
- 41. Optical telescope •The important properties of the telescope are sensitivityand resolution •Resolution(分辨能⼒): How small structure we can observe Angular resolution ∝ wavelength diameter（直径） •If the angular resolution is smaller, we can observe smaller objects. Thus, a larger telescope has better resolution. ＜
- 42. Optical telescope •The important properties of the telescope are sensitivityand resolution •Resolution(分辨能⼒): How small structure we can observe 10’ 1’ 5’’ 1’’ 1’(arcmin)=1/60° 1’’(arcsec)=1/360°
- 43. Optical telescope In summary…. A larger telescope has more sensitivity and more angular resolution. But, of course, we cannot make the unlimited large telescope because of technically and financial problems.
- 44. Optical telescope (TMT is under construction) •The comparison of optical telescope.
- 45. Current observational frontier •In 2022, JWST was launched as the successor to Hubble Space Telescope (HST). •JWST is larger mirror than HST •Thus, the sensitivity is better than HST ! JWST HST 2.4m 6.5m
- 46. HST JWST Images by JWST •The galaxy cluster observed by JWST is more clear than by past telescopes.
- 47. HST JWST Images by JWST •The Carina Nebula (star forming region) observed by JWST is more clear than by past telescopes.
- 48. Radio telescope •In addition to the optical telescope, we can also use a radio telescope to observe radio wavelength. For example, we use single-dish type radio telescope FAST(China) Green Bank telescope (USA) •This kind of single dish telescope is similar to optical telescopes
- 49. Radio telescope Angular resolution ∝ wavelength diameter（直径） Remember angular resolution. •Optical wavelength: ∼ 10−7 m •Radio wavelength: ≳ 1mm •Because smaller angular resolutions can resolve smaller scales, the angular resolution of radio wavelength is times worse! 104 Then, let’s make the diameter larger to obtain good angular resolution! Of course, there is a limitation of the diameter of a single dish… •The angular resolution of a single dish radio telescope is nog good
- 50. Radio telescope Angular resolution ∝ wavelength diameter（直径） Remember angular resolution. •Optical wavelength: ∼ 10−7 m •Radio wavelength: ≳ 1mm •Because smaller angular resolutions can resolve smaller scales, the angular resolution of radio wavelength is times worse! 104 Then, let’s make the diameter larger to obtain good angular resolution! Of course, there is a limitation of the diameter of a single dish… •The angular resolution of a single dish radio telescope is nog good
- 51. Radio interferometer •If we use a single dish, we cannot avoid the limitation of the diameter of a single dish. But, we have a good idea! We regard many antenna as “one” dish •This kind of radio telescope is called a radio interferometer（射电⼲涉仪）
- 52. Radio interferometer •In radio interferometer, if the distance between 2 antennas is large, the angular resolution becomes better. Angular resolution ∝ wavelength D [rad] •Angular resolution in radio interferometer is expressed by D 1∘ = π 180 [rad]
- 53. Let’s calculate! Angular resolution = wavelength D 1∘ = π 180 [rad] •This image is planet-forming disc around young star (I explain detail next week.) •The spatial resolution of this image is roughly 30 milli ( ) arcsec. If we use 3mm wavelength electromagnetic wave, How large size telescope is required to observe this image? 30 × 10−3 1’’(arcsec)=1/360° (Answer)
- 54. Let’s calculate! Angular resolution = wavelength D 1∘ = π 180 [rad] •This image is planet-forming disc around young star (I explain detail next week.) •The spatial resolution of this image is roughly 30 milli ( ) arcsec. If we use 3mm wavelength electromagnetic wave, How large size telescope is required to observe this image? 30 × 10−3 1’’(arcsec)=1/360° (Answer) 3 × 10−3 × ( 1 360) ∘ × π 180 = 3 × 10−3 m D[m] D ∼ 2km
- 55. ALMA telescope •ALMA telescope is sub-mm & mm radio interferometer located at Chili, Atacama. •ALMA provides us exiting scientific results.
- 56. Current observational frontier •EHT is located all over the world to achieve good angular resolution. •This is the first image of blackhole seen by human being ! •Event Horizon Telescope (EHT) is radio interferometer targeting to observe black hole images ∼ 10−6 arcsec Angular resolution ∝ wavelength D ~1000km •The angular size of blackhole shadow is arcsec ∼ 10−6
- 57. Future telescope •SKA radio telescope will start observation in 2027. •Science target: When do first stars and galaxies form? Is there life in the universe? •China is a membership of SKA.
- 58. SKAO
- 59. SKAO
- 60. Current observational frontier •Not only electromagnetic waves but also gravitational waves had been detected by LIGO and Virgo. LIGO detectors •We observed the gravitational wave from merging black holes in 2015. •Gravitational wave was predicted by Einstein in 1915.
- 61. Current observational frontier •Not only electromagnetic waves but also gravitational waves had been detected by LIGO and Virgo. LIGO detectors •We observed the gravitational wave from merging black holes in 2015. •Gravitational wave was predicted by Einstein in 1915.
- 62. Summary • In order to observe the universe, we use telescopes. • There is a kind of telescope corresponding to wavelength. • We can see the di ff erent universe when we use di ff erent wavelengths. • A gravitational wave is one of the tools to observe the universe. • Recently, there has been many surprising observation results.