SpaceToday's Image

Swimming up sky and up river

Night sky chart with constellations and objects labeled.
View larger. | Chart showing Mercury on Tuesday, May 11, 2021, 45 minutes after sunset as seen from 40 degrees N. latitude. The arrows through Mercury, the sun, Venus, and Mars show their movements, against the starry background, over a span of 5 days. You can see that Mercury is eastering faster than the sun; it will slow toward May 17, the date of its greatest distance from the sun in our sky. Image via Guy Ottewell.

Guy Ottewell originally published these charts on May 10, 2021, at his blog. Reprinted here with permission.

Little Mercury, elusive in the sun’s glare, is becoming more and more findable in the dusk, as it climbs toward its easternmost elongation – its greatest angular distance from the sun in our sky – on May 17, 2021. That will be its highest evening appearance of the year, for our Northern Hemisphere.

This year, Mercury swings three and a half times into the evening sky and three times into the morning sky. The graph below summarizes Mercury’s three morning and three-and-a-half evening appearances of the year.

Graphs of Mercury's appearances in the sky in 2021.
View larger. | This graph compares Mercury’s 3 morning and 3 1/2 evening appearances of 2021, using gray for the evening and blue for the morning excursions. The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40° north (thick line) and 35° south (thin), with maxima reached at the parenthesized dates below (40° north bold). Image via Guy Ottewell.

Meanwhile, in the Blue Planet Department

On the evening of May 9, another small wanderer – as the originally Greek word planet means – a young minke whale, about four yards long, reached an extreme elongation from the sea. That is, se (my pronoun, which I’d rather use than “he or she” or “it”) swam up the river Thames to the farthest point possible: the Richmond lock, which partially stops the tidal river.

At the side of the lock is a line of rollers on which boats can be pulled past. The tide must have been slightly over them, and the whale tried to get through, and became stuck.

This was about 7 a.m. A team from the London fire brigade and the Royal National Lifeboat Institute managed to get hem off the rollers by 1 a.m. Se was towed downriver, but at Isleworth – where we live – se broke free, swam away, and disappeared. Latest we know is that the public is asked to report any sighting of the whale, which is not in good health.

Read more about the whale at Guy Ottewell’s blog, or read about the whale’s fate here.

A young whale stuck in a narrow concrete channel.
Photo via Guy Ottewell.

Bottom line: Two beautiful charts by Guy Ottewell, one showing Mercury’s movement in the western sky at dusk around May 11, 2021, and the other comparing Mercury’s six appearances in our sky this year.

Via Guy Ottewell

May 10, 2021

Like what you read?
Subscribe and receive daily news delivered to your inbox.

Your email address will only be used for EarthSky content. Privacy Policy
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

More from 

Guy Ottewell

View All