# Tag Info

## Hot answers tagged observational-astronomy

43

The Moon is so close that establishment of an atmosphere would be easy: you take a photo. An atmosphere always is thicker at the surface and gets exponentially thinner outward. This would be visible at the edges of the moon. Just think of the photos of Earth from space with the blue-ish layer the atmosphere shows as. It would also mean that the edges of the ...

26

19th century observers determined that the Moon is (almost totally) airless using 19th century instruments and observing techniques. Roger Joseph Boscovich (1711-1787) is credited with having discovered that the Moon has no atmosphere in 1753. Wilhelm Beer and Johann Heinrich Mädler established the same conclusion in the 1830s: They also produced the first ...

21

The CMB is produced as the ionisation fraction of hydrogen falls from a high value to a very small value. Contrary to what is written in the Quora answer you may have been misled by, this happens at a temperature of about 3000 K. The value given by 13.6 eV/$k_B$ (remember to multiply by the electric charge to put the energy in SI units) is not even "...

13

It could take a day to discover a planet, if the stars align (literally), and then probably less than a year to find all five planets. On the 3rd of April 2020 you happen to look up and you notice that the evening star is right in the middle of the Seven sisters (you know the seven sisters because it does look rather special in the sky and the evening star ...

10

There are approved proposals for Cycle 1 to point the JWST at The Jovian system Jupiter's great red spot Mars Saturn and its moons and rings In those PDFs, they describe exactly what instruments they want to point where, but to summarize as far as I can tell they're planning to try to use pretty much all of the available instruments to image Jupiter and ...

9

This is a pure knowledge question. Suppose you were shown a map of Asia. Could you identify India, China, Burma, etc. Yes, if you had learnt the countries, although they are basically random patterns. You recognise patterns. The bright star Vega, and the parallelogram of the lyre are very distinctive. What is next to Vega? That would be Hercules. ...

7

When NASA says 5:50PM today, what location and/or timezone are they referring to? This particular website (eyes.nasa.gov) is using your system's local time to tell you the closest approach in your timezone. So when it says 5:50 PM today, it is when your clock reads 5:50 PM. Just be warned, if you have your system set to something else or possibly if you're ...

7

All modes can be used. But for bright targets, observations are limited to specific filters, subarrays, regions of the target planet, or spectral intervals. James Norwood and colleagues wrote a paper on this topic, although the full answer is complicated because of the "subset of the instrument modes" part. The simplest answer to understand is for ...

6

It's geomety: The day has 24 hours. The circle has 360°. So the sky "moves" 15° per hour due to the Earth's rotation of 360° in 24 hours once around its axis. Assuming that an object is approximately fixed at an infinitely distant place within this time span (not true for solar system objects, but as rule of thumb it's ok), an object on the ...

5

If handwritten notes of visual observation are valid, a good candidate is the observation of Neptune by Galileo in 1612, 234 years before the actual discovery. Also available without paywall here

4

Yes. Assuming that the moon is distant enough to neglect parallax effects, the semi major axis is just the radius of the moon, $r$, and the semi minor axis is $|r\cos\theta|$ where $\theta$ is the Sun-Moon-Earth angle. So when the sun is behind the Earth, the angle is 0 and the ellipse is a circle (full moon) so the semiminor axis = $r$. When the sun is ...

3

The JPL Small Body Database shows this asteroid having a close approach to Earth at Jan 18 21:51 TDB or 21:50 UTC. NASA Eyes shows me that time in my local time zone. JPL HORIZONS estimates it peaking at magnitude 10.2 a few hours earlier on the 18th, and magnitude 12 or brighter from January 15 to 20. The naked eye is limited to magnitude 6 at best, so this ...

3

How does IXPE measure polarization? Short answer: Electrons in the detector are preferential emitted in the direction of the polarization of the incident photon and then detected. Quoting from NASA's IXPE: Polarization Detection page: IXPE will have three identical X-ray telescopes, with polarization detectors at each focus. The detectors, called Gas Pixel ...

3

The "velocity" of something at high redshift isn't particularly meaningful and is not generally used, since cosmological redshift should not really be thought of as a velocity-related Doppler shift. Indeed this velocity exceeds the speed of light above redshifts above 1.5. There is a correspondence between recession velocity, distance (you have to ...

3

Please suggest some good sources where I can study this? There are many software and internet-based solutions that you can use a computer or even a smartphone to solve this. I like in-the-sky.org in planetarium mode (shown below). I chose Nagpur near the geographical center of India and 5:30 AM 24-Dec-2019, which is not a perfect match to the horizon but it'...

3

Absolutely! The Bol’choï Teleskop Azimutal’ny (Large Azimuth Telescope), built by the former USSR in 1979 and the largest telescope in the world from then until the Gemini telescopes were built in 1999—BTA has a diameter of 6 metres—uses an azimuth mount. Obviously, any long-exposure imaging done with it requires a field derotator. Read more about it here.

3

This is an answer that I am writing up based on comments by ProfRob and Mike G. The meaning of 'beta' in these plots is the slope of the line. The figure itself is from Radio spectral properties of star-forming galaxies in the MIGHTEE-COSMOS field and their impact on the far-infrared-radio correlation (arXiv link). From the caption of the figure in the ...

2

The spacetime geometry of the universe is determined by the total energy density, which includes contributions from matter (including dark matter), dark energy, radiation and curvature (if non-zero). In the present-day universe the sum of these, dominated by matter and dark energy, adds up to something that is consistent with the critical density and the ...

2

Can I use 75mm Plano convex lens with 1000mm focal length tl;dr: Go for it! First see this answer to Will these simple 2 convex lens arrangement telescope see the moon clearly? but your question is quite different, not a duplicate and I think you can have some success! You will have some chromatic aberration but at f/12.5 it won't be so strong, and you ...

2

The two values are the peculiar velocity of the local group relative to the Cosmic microwave background The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be moving at 627±22 km/s [390±14 mps ] in the direction of galactic longitude ℓ = 276°±3°, b = 30°±3° Or the peculiar velocity of the solar system relative to the CMB: ...

2

In the video, the white dots represent 14000 asteroids, and the green tracks are 200 of the brightest asteroids. These are from standard catalogues. Gaia has detected about 1700 asteroids, but most of these were already known. The video shows four newly discovered object, in pink. They have provisional designations 2018 YK4, 2018 XL4, 2018 YM4 and 2019 CZ10....

2

Light pollution, Haze or any kind of Air pollution will affect the intensity of the image or to say more, you will have a less bright image or bit hazy which will in turn affect the efficiency of the magnification you should get. but it shouldn't appear as if it is out of focus. In my telescope collection, I have a Celestron 130EQ which has similar specs ...

2

TL;DR: get a 2x Barlow first - it's cheaper than an eyepiece and can be used with both of your 1.25" eyepieces. If it works well and fiddling about with eyepieces and the Barlow in the dark gets a bit annoying, then look at buying a dedicated eyepiece. A common wish when first looking at planets is to want to push the magnification as high as possible. ...

1

The jump occurs at the redshifted wavelength of the Lyman-$\alpha$ line, so this is the Gunn-Peterson trough, which is caused by neutral hydrogen in the intergalactic medium suppressing any radiation with shorter wavelengths for sufficiently distant quasars. This is a limiting case of the Lyman-$\alpha$ forest formed by the absorption lines caused by all the ...

1

tl;dr Size plays a role in this very specific scenario in kind of an indirect way, but generally speaking, variability in its enormous scope depends on a lot of other things more for other kinds of objects, and this is not a relation to be applied outside of maybe pulsars (probably) Let me know if some of these assumptions I’m making here are wrong, but I’m ...

1

The focal reducer doesn't do that. In order to build an apochromatic refractor , that has minimal chromatic aberration, you need an objective lens assembly composed of 3 lenses. In order to reduce the spherical aberration and have a flat field, you need an additional lens element called field flattener. Hope this helps a bit

1

The declination ($\delta$) of the celestial pole is 90°. Therefore the angle $\alpha=90-\delta$ and 2 times that value would be $180-2\delta$. Two Alpha is not the declination. The zenith distance is the angle measured from the zenith. I have added that angle (to the upper culmination) in this diagram: The zenith distance at upper culmination would be \$(90-\...

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