Starship Asterisk*

Mars Approach 2020

Explanation: Look to the east just after sunset tonight and you'll see a most impressive Mars. Tonight, Mars will appear its biggest and brightest of the year, as Earth passes closer to the red planet than it has in over two years -- and will be again for another two years. In a week, Mars will be almost as bright -- but at opposition, meaning that it will be directly opposite the Sun. Due to the slightly oval shape of the orbits of Mars and Earth, closest approach and opposition occur on slightly different days. The featured image sequence shows how the angular size of Mars has grown during its approach over the past few months. Noticeably orange, Mars is now visible nearly all night long, reflecting more sunlight toward Earth than either Saturn or Jupiter. Even at its closest and largest, though, Mars will still appear over 100 times smaller, in diameter, than a full moon.

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Oh Yeah; Should be some probes approaching Mars also!

APOD Robot wrote: ↑Tue Oct 06, 2020 4:05 am Mars Approach 2020

Explanation: Look to the east just after sunset tonight and you'll see a most impressive Mars. Tonight, Mars will appear its biggest and brightest of the year, as Earth passes closer to the red planet than it has in over two years -- and will be again for another two years. In a week, Mars will be almost as bright -- but at opposition, meaning that it will be directly opposite the Sun. Due to the slightly oval shape of the orbits of Mars and Earth, closest approach and opposition occur on slightly different days. The featured image sequence shows how the angular size of Mars has grown during its approach over the past few months. Noticeably orange, Mars is now visible nearly all night long, reflecting more sunlight toward Earth than either Saturn or Jupiter. Even at its closest and largest, though, Mars will still appear over 100 times smaller, in diameter, than a full moon.

Dumb question: can the earth ever cast a shadow on mars? Or, does the earth ever eclipse the sun on mars? Or does the earth ever transit the sun on mars? I guess it would be a lot to ask for the geometry to line up well enough to allow that.

Based on a Facebook comment by Daniel Hiron, I re-calculated the relative angular size more exactly as 1779.8"/22" = about 80.9.

I found the angular size of Mars on Oct 6, 2020 from this site:
https://in-the-sky.org/graphs.php?gtype ... obj1txt=P4
and the angular size of the Moon from this site:
https://svs.gsfc.nasa.gov/4768

I therefore changed the wording of today's NASA APOD from "over 100 times smaller" to "about 100 times smaller". I apologize for the oversight. - RJN

johnnydeep wrote: ↑Tue Oct 06, 2020 3:32 pm Dumb question: can the earth ever cast a shadow on mars? Or, does the earth ever eclipse the sun on mars? Or does the earth ever transit the sun on mars? I guess it would be a lot to ask for the geometry to line up well enough to allow that.

Not a dumb question! Please see: https://en.wikipedia.org/wiki/Transit_o ... _from_Mars

johnnydeep wrote: ↑Tue Oct 06, 2020 3:32 pm

APOD Robot wrote: ↑Tue Oct 06, 2020 4:05 am Mars Approach 2020

Explanation: Look to the east just after sunset tonight and you'll see a most impressive Mars. Tonight, Mars will appear its biggest and brightest of the year, as Earth passes closer to the red planet than it has in over two years -- and will be again for another two years. In a week, Mars will be almost as bright -- but at opposition, meaning that it will be directly opposite the Sun. Due to the slightly oval shape of the orbits of Mars and Earth, closest approach and opposition occur on slightly different days. The featured image sequence shows how the angular size of Mars has grown during its approach over the past few months. Noticeably orange, Mars is now visible nearly all night long, reflecting more sunlight toward Earth than either Saturn or Jupiter. Even at its closest and largest, though, Mars will still appear over 100 times smaller, in diameter, than a full moon.

Dumb question: can the earth ever cast a shadow on mars? Or, does the earth ever eclipse the sun on mars? Or does the earth ever transit the sun on mars? I guess it would be a lot to ask for the geometry to line up well enough to allow that.

As noted by RJN, the Earth can transit the Sun from Mars. But its angular size is very small compared with the Sun, so it doesn't "cast a shadow" on Mars in any meaningful sense. The intensity of the Sun would merely be reduced by a tiny fraction of a percent.

RJN wrote: ↑Tue Oct 06, 2020 5:09 pm

johnnydeep wrote: ↑Tue Oct 06, 2020 3:32 pm Dumb question: can the earth ever cast a shadow on mars? Or, does the earth ever eclipse the sun on mars? Or does the earth ever transit the sun on mars? I guess it would be a lot to ask for the geometry to line up well enough to allow that.

Not a dumb question! Please see: https://en.wikipedia.org/wiki/Transit_o ... _from_Mars

Cool stuff! One small tidbit from the article:

No one has ever seen a transit of Earth from Mars, but the next transit will take place on November 10, 2084.[1] The last such transit took place on May 11, 1984.[2]

During the event, the Moon could almost always also be seen in transit, although due to the distance between Earth and Moon, sometimes one body completes the transit before the other begins (this last occurred in the 1800 transit, and will happen again in 2394).

Chris Peterson wrote: ↑Tue Oct 06, 2020 5:45 pm

johnnydeep wrote: ↑Tue Oct 06, 2020 3:32 pm
Dumb question: can the earth ever cast a shadow on mars? Or, does the earth ever eclipse the sun on mars? Or does the earth ever transit the sun on mars? I guess it would be a lot to ask for the geometry to line up well enough to allow that.

As noted by RJN, the Earth can transit the Sun from Mars. But its angular size is very small compared with the Sun, so it doesn't "cast a shadow" on Mars in any meaningful sense. The intensity of the Sun would merely be reduced by a tiny fraction of a percent.

Yup, that makes sense.