Page 1 of 1
APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 4:05 am
by APOD Robot
Two Worlds, One Sun
Explanation: How different does sunset appear from Mars than from Earth? For comparison, two images of our common star were taken at
sunset, one from Earth and one from Mars. These images were scaled to have same angular width and
featured here side-by-side. A quick inspection will reveal that the
Sun appears slightly smaller from
Mars than from
Earth. This makes sense since
Mars is 50% further from the
Sun than
Earth. More striking, perhaps, is that the
Martian sunset is
noticeably bluer near the Sun than the
typically orange
colors near the setting Sun from Earth. The reason for the
blue hues from Mars is
not fully understood, but thought to be related to forward scattering properties of
Martian dust. The terrestrial sunset was taken in 2012 March from
Marseille,
France, while the Martian sunset was
captured in 2015 by
NASA's robotic
Curiosity rover from
Gale crater on
Mars. Last week a
new rover and a
helicopter -- onboard
Mars 2020 --
launched for Mars.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 8:10 am
by rj rl
Interesting, I thought the mechanism was well understood.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 8:16 am
by David Cooper
Note that the disc of the sun on Mars is not distorted by atmospheric refraction and remains undistorted.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 10:32 am
by orin stepanek
Interesting how the Earth sunset is orange; and the Mars sunset is blue!
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 10:53 am
by ozoneman@comcast.net
My theory on the blue sky is Earth has clouds, water and with our atmosphere is orange while Mars has no clouds and no water (moisture)?
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 11:14 am
by Ann
Let's not forget that Earth is blue and Mars is red!
As Ethan Siegel of Forbes wrote (and you may not necessarily agree):
Ethan Siegel wrote:
With our magnetic field intact, our planet will remain blue and alive for the foreseeable future.
Ann
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 1:16 pm
by neufer
Rayleigh scattering scatters out blue light.
Martian dust scatters out red light.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 1:51 pm
by Chris Peterson
rj rl wrote: ↑Sun Aug 02, 2020 8:10 am
Interesting, I thought the mechanism was well understood.
Yes and no. It is entirely a function of the scattering agents in the atmosphere- gas molecules and dust particles. But since the details of the particles in the martian atmosphere are not well known, the details of the scattering are also unknown.
The
principles of what's going on are extremely well described by current understanding; we're simply missing some of the inputs to the equations.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 2:56 pm
by skyping
Is "Two Worlds, One Sun" available for purchase as a wall poster? Very cool. Thanks David.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 4:03 pm
by Cousin Ricky
ozoneman@comcast.net wrote: ↑Sun Aug 02, 2020 10:53 am
My theory on the blue sky is Earth has clouds, water and with our atmosphere is orange while Mars has no clouds and no water (moisture)?
The reason for our blue sky on earth is Rayleigh scattering. It has nothing to do with water or clouds. Our sky turns orange at sunset because, with a longer path for sunlight to travel through, the blue gets scattered away.
The Martian sky is beige because of all the dust in the atmosphere. But there is not enough atmosphere to scatter the sunlight until sunset. BTW, Mars does have clouds, just not as much as Earth.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 4:06 pm
by Cousin Ricky
Earth: blue sky and orange sunsets.
Mars: orange sky and blue sunsets.
How poetic! Or is it contrarian?
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 5:25 pm
by Hmm
Imagine if it were possible to see what the sunset looks like from one of the "habitable zone" planets some day? Kepler 452b, for instance.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 8:34 pm
by Boomer12k
Eight worlds... one Sun...
Nice comparison ....
I was out looking at the sky about 1am... I had gotten an earlier shot of the Moon with Saturn and Jupiter on either side... but around 1am went out again... and in the east was startled to see a big red star... and I wondered and wondered what it could be... so checked with software and it was MARS!!!! LOL... I had not seen it for some time...and did not expect it to be so bright... Hope to get some shots soon...
:---[===] *
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Sun Aug 02, 2020 8:40 pm
by Chris Peterson
Boomer12k wrote: ↑Sun Aug 02, 2020 8:34 pm
Eight worlds... one Sun...
Nice comparison ....
I was out looking at the sky about 1am... I had gotten an earlier shot of the Moon with Saturn and Jupiter on either side... but around 1am went out again... and in the east was startled to see a big red star... and I wondered and wondered what it could be... so checked with software and it was MARS!!!! LOL... I had not seen it for some time...and did not expect it to be so bright... Hope to get some shots soon...
:---[===] *
Same thing happened to me a few nights ago. Was walking from my observatory back up to the house and noticed the bright red object low in the east. Wasn't expecting it, because I haven't been paying attention to Mars lately, but didn't need to look it up. There are no red stars that bright, and none in that part of the sky. Nothing else it could be.
Re: APOD: Two Worlds, One Sun (2020 Aug 02)
Posted: Mon Aug 03, 2020 3:12 pm
by Cousin Ricky
Boomer12k wrote: ↑Sun Aug 02, 2020 8:34 pm
I was out looking at the sky about 1am... I had gotten an earlier shot of the Moon with Saturn and Jupiter on either side... but around 1am went out again... and in the east was startled to see a big red star... and I wondered and wondered what it could be... so checked with software and it was MARS!!!!
Saturn does this to me all the time, though once I have a fix on it for the season, it doesn’t fool me again... until the next year.
