San Diego Mountain Lilac (ceanothus cyaneus), on the right (east) fork of the Rattlesnake Canyon trail, in Poway.

Tree Heights can be easily measured this week if the sun shines at midday. On or near February 18, at or very near 12 noon, the sun as seen from San Diego County stands at an altitude of 45 degrees above the horizon. Under those conditions, the length of a shadow cast by a vertical tree trunk on a horizontal surface equals the height of the tree trunk. Even if you lack a measuring tape, you can still use your own feet to pace the distance heel-to-toe: the length of an average adult male's shoe sole, for example, is very close to one foot.

Ceanothus, or wild lilac, begins its annual blooming cycle this month — at least in the warmer coastal areas. Assuming sufficient rainfall arrives, by sometime in March virtually every chaparral-covered canyon and hillside on the coastal strip may exhibit blue or white-flowering specimens. The peak of the ceanothus bloom will work its way eastward, reaching Ramona and Alpine by March or April, and the Palomar, Cuyamaca, and Laguna mountains by April or May. Ceanothus growth was rampant in Cuyamaca Rancho State Park, where the devastating 2003 Cedar wildfire incinerated nearly all of the trees, and opened up opportunities for post-fire, pioneering vegetation such as the ceanothus species.

La Jolla tidepools

Photograph by Matthew Suárez

Very Low Tides this week coincide with optimum times of day for tidepooling: Thursday, February 18 at 6:38 p.m. (-2.13 feet); Friday at 7:07 p.m. (-2.59 feet); Saturday at 9:39 p.m. (-2.89 feet). Very high tides will also occur within that string of days, Thursday at 1:08 a.m. (+4.53 feet); Friday at 2:02 a.m. (+4.46 feet); and Saturday at 3:19 a.m. (+4.53 feet).

Have you ever seen Canopus, the second-brightest star after Sirius? In one of the interesting coincidences known to devoted skywatchers, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a very flat south horizon. Canopus crosses the south point on the horizon just 21 minutes before Sirius does.

When to look? Canopus is due south when Beta Canis Majoris — Murzim the Announcer, the star about three finger-widths to the right of Sirius — is at its highest due south over your landscape. That's probably sometime between 8 and 9 p.m. now, depending on how far east or west you live in your time zone. Look straight down from Murzim then.

The above comes from the Outdoors listings in the Reader compiled by Jerry Schad, author of Afoot & Afield in San Diego County. Schad died in 2011. Planet information from SkyandTelescope.org.