55 votes
Accepted

In this image taken by Voyager 1, which is closer: the earth or the moon?

I used JPL Horizons to get the position vectors of each relative to the SSB on Sep 19, 1977. ...
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  • 2,522
53 votes
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How do we have photos of galaxies so far away?

There are two reasons that often — but not always — light from galaxies millions and even billions of lightyears away make it through the Universe and down to us: Particle number and particle size ...
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53 votes

Why does the alignment evaluation image from JWST look like this?

A quick check by pasting the image into PowerPoint and rotating a line shows that the spikes have threefold symmetry; they're at -30°, 30° and 90°. This is exactly what you would see from diffraction ...
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  • 32.4k
50 votes

In this image taken by Voyager 1, which is closer: the earth or the moon?

Another way to look at it is by linear measurements. Using Photoshop, and averaging three measures each of the Moon and the Earth (with the “Ruler” tool), I get 12.56 pixels for the Moon and 54.67 ...
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47 votes
Accepted

Why does the alignment evaluation image from JWST look like this?

Any telescope will have diffraction of the light due to the edges between mirror and non-mirror. This sets a fundamental limit to the telescope's resolution, given by the size of its primary mirror. ...
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44 votes
Accepted

Does this smartphone photo show Mars just below the Sun?

That is a camera artefact caused by the bright sunlight reflecting within the lens on your phone. It’s more pronounced than on a large camera because of the small lens size. This is a secondary image ...
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  • 577
38 votes

Please check my Mars photo

(Much of this echoes what antlersoft says in their answer) For a phone photo through the eyepiece that looks about right to me! The size... the brightness... both are as I expect. What you could try ...
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  • 1,498
30 votes

Help understanding this unsettling image of Titan, Epimetheus, and Saturn's rings?

This NASA page says this photo was taken on April 28 2006. Using Celestia, I managed to find the picture from Cassini that best lines up with the photo. It doesn't match up precisely, but that's to ...
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  • 3,958
30 votes
Accepted

Which planet is this (if any)?

Stellarium shows the Moon and Mars very close together in the sky tonight (Saturday, 3rd October 2020), so yes, it was probably Mars that you saw. Moon and Mars on 2020/10/03 (Stellarium) Stellarium ...
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  • 1,536
29 votes
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Which part of the milky way does the image show?

I wholeheartedly recommend astrometry.net for this sort of thing. It Just Works(tm); running on your image produced this output with absolutely no hints or guidance from me: For avoidance of doubt, I ...
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26 votes

How do we have photos of galaxies so far away?

As Rob Jeffries says, the universe is mostly empty space. A photon can easily travel thousands of light years without interacting with anything. Most of the interaction would occur when photons ...
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  • 4,336
25 votes
Accepted

Why is there no color shift on the photo of the M87 black hole?

The picture isn't a "colour" picture - it is monochrome. i.e. It is obtained at a single microwave wavelength of 1.3 mm, and so not at any wavelength you could see (Akiyama et al. 2019). ...
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  • 118k
23 votes

How do we have photos of galaxies so far away?

There's a misconception in your question I don't think the other answers have addressed. If light emitted from the galaxy travels in all directions, then how is it that we can still map out the ...
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23 votes

Why does the closest approach of star S2 to Sgr A* not appear to be near the focus of its elliptical orbit?

The orbital elements are on wikipedia: $$e=0.884\ a=0.125'',\ i=134^\circ,\, \Omega=228^\circ$$ (At an assumed distance of 8kpc, $0.125'' = 1000au$) It is the inclination that means that the black ...
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  • 91k
20 votes

Please check my Mars photo

It's very difficult to get any kind of picture just holding your phone up to the eyepiece, and the picture you posted is overexposed and probably motion-smeared, but other than that it's what you'd ...
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  • 2,831
20 votes
Accepted

Finding Scorpio in the Milky Way panorama

Antares is actually quit easy to spot. It is just north of the the galactic centre. Once you have Antares, you can piece together the rest of Scorpio, It is rather hard, because there are too many ...
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  • 91k
18 votes
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What did I photograph?

A contrast stretch reveals stars down to magnitude 4 or 5. The stars you asked about are Deneb (center) and Vega (bottom). The constellation in the center and below is Cygnus; we also see Cepheus at ...
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18 votes
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What's the white glow around this star?

Astrometry.net has identified your star field as being part of the Andromeda constellation. The diffuse object in the centre of your image is the Andromeda Galaxy (Messier 31). The bright star to the ...
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  • 1,536
18 votes
Accepted

Which are stars and which are noise in this comet photo?

Is that right? Yes. Is the fuzzy one an extended object? That would certainly be my guess (probably a distant galaxy). What causes so many isolated pixels to be so much brighter ...
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  • 14.9k
18 votes

In this image taken by Voyager 1, which is closer: the earth or the moon?

note: this confirms @GregMiller's answer I started typing it last night and fell asleep; woke up and finished it and clicked "post" then to discovered a bunch of new answers. For those who ...
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  • 32.4k
17 votes
Accepted

How far into intergalactic space would you have to go to see the Milky Way?

We can calculate the distance we need to be from an object in order for it to be any arbitrary angular size using the formula $D=\frac{d}{2\tan(\frac12\delta)}$. In this case, $D$ is the distance ...
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  • 3,046
17 votes

Jupiter with a mobile phone and Celestron Astro FI 102mm Maksutov

Congratulations on your purchase. The first pictures dont' show anything much. Just a out-of-focus blur. The last one shows Jupiter and three of its moons. I've overlaid the image onto a simulated ...
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  • 91k
17 votes
Accepted

How bright is it on Pluto in the middle of the day?

Back when New Horizons was preparing for its flyby back int 2015, NASA's website set up a tool to allow you to experience the brightness of light at High Noon on the subsolar point on Pluto. From ...
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  • 3,369
15 votes

Attach a visible light telescope to the outside of the ISS

A self-sufficient orbiting telescope is basically Hubble mkII and would never get off the ground, literally and metaphorically Hubble was expensive because it was state-of-the-art, requiring ...
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  • 2,956
15 votes

Does this smartphone photo show Mars just below the Sun?

Stellarium shows Mars close to the Sun and just above the horizon at that date and time. Unfortunately, Mars is only 2° above the horizon (and also on the other side of the Sun to the Earth), so it is ...
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  • 1,536
15 votes

In this image taken by Voyager 1, which is closer: the earth or the moon?

The Earth was closer. I can't find the time when that picture was taken. That NASA press release is dated Sep 19, 1977, but the consensus seems to be that the photo was taken around the 18th of ...
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  • 10.4k
14 votes

How do we have photos of galaxies so far away?

Sorry if this logic seems a bit circular, but we can get unobscured pictures of galaxies because they are unobscured. As has been mentioned - space is really, really big and really, really empty. ...
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  • 269
13 votes
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Astrophotography - Unable to achieve focus with current setup

Yes, the vast majority of small telescopes made for visual observations (like most dobsonians and other newtonian-based architectures) have very limited back focus. In other words, with the focuser ...
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