This Week’s Sky at a Glance, 2021 May 15 – 22 ~by Curt Nason
This week stargazers have an opportunity to do an ISS marathon. The International Space Station orbits the earth at an altitude of about 400 km, and at this height it completes an orbit in approximately 90 minutes. The ISS has large solar panels that reflect sunlight earthward which make it bright enough to rival Jupiter and Venus at times. We can usually catch it once or twice in morning twilight for a period of about ten days, then in the evening twilight for the same stretch, and then it is unseen for a while as the overhead passes are in daylight or shadow. For a few weeks either side of the summer solstice, when we have long periods of twilight, the ISS can be seen four or five times from evening through to morning. If you see it in each pass throughout the night you have completed the ISS marathon.
To determine when and where to look I use the website Heavens-Above, but there are other apps such as Satellite Safari that give the same information and may even give you an alert when a pass is about to occur. Heavens-Above defaults to zero degrees latitude and longitude so be sure to enter your location. Information includes the date and time, brightness, and altitude and azimuth of when it is first visible (usually ten degrees above the horizon), at its highest, and when it disappears into earth’s shadow or below ten degrees. Brightness is given in stellar magnitude, where the lower the number the brighter is the object, and the ISS is usually bright enough to be a negative number (magnitude -3 is about 2.5 times brighter than -2). With the Heavens-Above website, clicking on the date brings up a sky map showing the path of the ISS through the constellations. Since earth rotates under the satellite, the path through the constellations will differ with each pass but it is always approximately west to east.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 5:46 am and sunset will occur at 8:45 pm, giving 14 hours, 59 minutes of daylight (5:54 am and 8:47 pm in Saint John). Next Saturday the Sun will rise at 5:36 am and set at 8:53 pm, giving 15 hours, 14 minutes of daylight (5:46 am and 8:55 pm in Saint John).
The Moon is near Mars this Saturday to toast International Astronomy Day, and after sunset on Tuesday use a telescope to view the Lunar X just inside the shadow line below the Moon’s equator. On Wednesday the Moon is at the first quarter phase. Mercury is at its greatest elongation from the Sun on Monday, after which it begins a ten day trip toward a rendezvous with Venus between the horn tips of Taurus the Bull. Jupiter rises around 2:30 am midweek, 45 minutes after Saturn.
With astronomy meetings and outreach activities on hold, you can watch the local Sunday Night Astronomy Show at 8 pm and view archived shows.
Questions? Contact Curt Nason.